Backend developers, renowned for their in-depth mastery of server-side technologies, stand as vital components in nearly all application development teams.<\/p>\n\n\n\n
\nAccording to the CoderPad 2024 Developer survey<\/a>, backend developers are the the second-most in-demand job role technical recruiters are looking to fill.<\/p>\n<\/blockquote>\n\n\n\nIn the subsequent sections, you will find an array of practical coding tasks and interview questions designed to assess the technical competence of backend developer candidates during evaluations.<\/p>\n\n\n\nAdditionally, we have included a selection of endorsed best practices to aid in a reliable assessment of candidates’ backend skills through your interview queries.<\/p>\n\n\n\nTable of Contents<\/h2>Backend example questions<\/a>Question 1: Create a CRUD API<\/a><\/ul><\/li>Question 2: Shopping List<\/a><\/ul><\/li><\/ul><\/li>Junior backend interview questions<\/a><\/li>Intermediate backend developer questions<\/a><\/li>Senior backend developer questions<\/a><\/li>More backend interview resources<\/a><\/li>Best interview practices for backend roles<\/a><\/li><\/ul><\/nav><\/div>\n\n\n\nBackend<\/strong> example questions<\/strong><\/h2>\n\n\n\nQuestion 1: Create a CRUD API<\/strong><\/h3>\n\n\n\nThe goal of this exercise is to retrieve data from an external source, store it in an appropriate database structure, and create a CRUD RESTful API to interface with the database<\/p>\n\n\n\nGoals<\/h4>\n\n\n\n1. Read the data from this graphql endpoint: https:\/\/swapi-graphql.netlify.app\/.netlify\/functions\/index<\/a> with the following query:<\/p>\n\n\n\nquery Query {allPlanets{planets{name population terrains climates}}}<\/code><\/p>\n\n\n\n(View the shape of the data here<\/a>.)<\/p>\n\n\n\n2. Store the data from the graphql endpoint into the database and create appropriate models<\/p>\n\n\n\n3. Write RESTful Create, Read, Update, and Delete endpoints to interact with the database<\/p>\n\n\n\n\t<\/iframe>\n<\/div>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"question-2-shopping-list\"><strong>Question 2: Shopping List<\/strong><\/h3>\n\n\n\n<p>This question tests a candidate’s ability to create model(s) for the data structure, insert hard-coded data into a database, modify tables and fields in a database, and write endpoints to interact with data.<\/p>\n\n\n\n<p><strong>Part 1<\/strong><\/p>\n\n\n\n<p><em>Create a model for the shopping lists and items located in app\/data\/data.ts.<\/em><\/p>\n\n\n\n<p><strong>Part 2<\/strong><\/p>\n\n\n\n<p><em>Store the shopping lists and items located in app\/data\/data.ts in the database.<\/em><\/p>\n\n\n\n<p><strong>Part 3<\/strong><\/p>\n\n\n\n<p><em>Modify the database such that a price field can be stored for each item.<\/em><\/p>\n\n\n\n<p><strong>Part 4<\/strong><\/p>\n\n\n\n<p><em>Multiply the quantity of each item in the shopping lists by two.<\/em><\/p>\n\n\n\n<p><strong>Part 5<\/strong><\/p>\n\n\n\n<p><em>Create API endpoints to dynamically get a list of shopping lists and items.<\/em><\/p>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"assessing-the-candidate\"><strong>Assessing the candidate<\/strong><\/h4>\n\n\n\n<p>The candidate should create models for a shopping list and items. They should then write code to create the tables necessary and insert the data into the tables. Additionally, the candidate can be asked to edit the data in the tables and add additional fields. Finally, endpoints to interact with the data can be created.<\/p>\n\n\n<div\n\tclass=\"sandbox-embed responsive-embed sandbox-embed--full-width\"\n\tstyle=\"padding-top: 85%\"\ndata-block-name=\"coderpad-sandbox-embed\">\n\t<iframe src=\"https:\/\/embed.coderpad.io\/sandbox?question_id=254803u0026use_question_button\" width=\"640\" height=\"544\" loading=\"lazy\" aria-label=\"Try out the CoderPad sandbox\"><\/iframe>\n<\/div>\n\n\n<section class=\"\n\ticon-lists-block\n\t\n\" data-block-name=\"coderpad-icon-lists-block\">\n <div class=\"inner\">\n\n \n <div class=\"lists lists--2\">\n <div class=\"icon-list\">\n <div class=\"top\">\n <div class=\"icon-container\">\n <svg class=\"icon icon-lightning-bolt\" role=\"img\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" fill=\"none\" viewBox=\"0 0 10 14\"><title>lightning bolt<\/title><path fill=\"currentColor\" d=\"M3.608 13.967c.185.079.4.013.508-.158l4.922-7.82a.41.41 0 0 0-.347-.63H5.407L6.628.511a.41.41 0 0 0-.744-.32L.962 8.011a.41.41 0 0 0 .347.63h3.284l-1.221 4.848a.41.41 0 0 0 .236.478Z\"\/><\/svg>\n\n <\/div>\n \n <h3 class=\"title\">Backend skills to assess<\/h3>\n <\/div>\n\n <ul class=\"links\">\n <li>\n <a >Backend frameworks<\/a>\n <\/li>\n <li>\n <a >RESTful API design<\/a>\n <\/li>\n <li>\n <a >Databases and ORMs<\/a>\n <\/li>\n <\/ul>\n <\/div>\n\n <div class=\"icon-list\">\n <div class=\"top\">\n <div class=\"icon-container\">\n <svg class=\"icon icon-briefcase\" role=\"img\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" viewBox=\"0 0 25 26\" fill=\"none\"><title>briefcase<\/title><path fill=\"currentColor\" d=\"M5.469 16.125a5.446 5.446 0 0 1-3.907-1.648v6.335a2.35 2.35 0 0 0 2.344 2.344h17.188a2.35 2.35 0 0 0 2.343-2.343v-6.336a5.446 5.446 0 0 1-3.906 1.648H5.47Z\"\/><path fill=\"currentColor\" d=\"M21.094 5.969h-3.125v-.782a2.344 2.344 0 0 0-2.344-2.343h-6.25a2.344 2.344 0 0 0-2.344 2.344v.78H3.906a2.35 2.35 0 0 0-2.344 2.345v2.343a3.906 3.906 0 0 0 3.907 3.906h2.343V12.22a.781.781 0 1 1 1.563 0v2.344h6.25v-2.344a.781.781 0 1 1 1.563 0v2.344h2.343a3.907 3.907 0 0 0 3.907-3.907V8.312a2.351 2.351 0 0 0-2.344-2.343Zm-12.5-.782a.781.781 0 0 1 .781-.78h6.25a.781.781 0 0 1 .781.78v.782H8.594v-.782Z\"\/><\/svg>\n\n <\/div>\n \n <h3 class=\"title\">Backend job roles<\/h3>\n <\/div>\n\n <ul class=\"links\">\n <li>\n <a >Backend developer<\/a>\n <\/li>\n <li>\n <a >Software engineer<\/a>\n <\/li>\n <li>\n <a >Full-stack developer<\/a>\n <\/li>\n <\/ul>\n <\/div>\n\n <\/div>\n \n <\/div>\n<\/section>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"junior-backend-interview-questions\">Junior backend interview questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> What’s the difference between a framework and a library? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> A library is a collection of functions\/methods\/classes that you can call from your own code. You’re in charge of the flow of the application; you decide when to call the library. In contrast, with a framework, the flow is determined by the framework itself, invoking your code at specific points (Inversion of Control). Examples include Flask as a framework and NumPy as a library in Python.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Consider the following Python code snippet. Can you identify what’s wrong with it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def add_numbers(a, b):\n <span class=\"hljs-keyword\">return<\/span> a + b\n\n result = add_numbers(<span class=\"hljs-string\">\"5\"<\/span>, <span class=\"hljs-number\">3<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function <code>add_numbers<\/code> is trying to add a string (“5”) and an integer (3) together, which will raise a TypeError in Python. To fix it, one must ensure that both variables are of the same datatype, by converting the string to an integer.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain what a <code>JOIN<\/code> operation is in SQL. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> A <code>JOIN<\/code> operation in SQL is used to combine rows from two or more tables based on a related column between them. The most common types of JOINs include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Look at this SQL query and explain if there is any vulnerability:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> query = <span class=\"hljs-string\">\"SELECT * FROM users WHERE username = '\"<\/span> + username + <span class=\"hljs-string\">\"' AND password = '\"<\/span> + password + <span class=\"hljs-string\">\"';\"<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This query is vulnerable to SQL injection. An attacker can provide malicious input in <code>username<\/code> or <code>password<\/code> to modify the query and potentially access or harm the database. To prevent this, one should use parameterized queries or prepared statements.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Describe the concept of statelessness in RESTful APIs. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Statelessness means that each HTTP request from a client to a server must contain all the information needed to understand and process the request. The server should not store any context between requests, ensuring that each request can be understood in isolation.<\/p>\n\n\n\n<p><strong>Question:<\/strong> What’s the output of the following Python function?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> def mystery_function(a, b=[]):\n b.append(a)\n <span class=\"hljs-keyword\">return<\/span> b\n\n <span class=\"hljs-keyword\">print<\/span>(mystery_function(<span class=\"hljs-number\">1<\/span>))\n <span class=\"hljs-keyword\">print<\/span>(mystery_function(<span class=\"hljs-number\">2<\/span>))<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The output will be:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"JSON \/ JSON with Comments\" data-shcb-language-slug=\"json\"><span><code class=\"hljs language-json shcb-wrap-lines\"> [<span class=\"hljs-number\">1<\/span>]\n [<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">2<\/span>]<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JSON \/ JSON with Comments<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">json<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The mutable default argument (<code>b=[]<\/code>) is a common Python gotcha. The list <code>b<\/code> is created only once when the function is defined, so successive calls to the function reuse the same list.<\/p>\n\n\n\n<p><strong>Question:<\/strong> What is the most Pythonic way to check if a list is empty (considering you are sure the variable to test is a list) ?<\/p>\n\n\n\n<p><strong>Answer:<\/strong> <\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"><span class=\"hljs-keyword\">if<\/span> my_list:\n <span class=\"hljs-comment\"># do something when list is not empty<\/span>\n<span class=\"hljs-keyword\">else<\/span>:\n <span class=\"hljs-comment\"># do something when list is empty<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>It is not necessary to compare it with <code>== []<\/code> or to call <code>len(my_list)<\/code>. When used in a condition, the empty tuples, lists, dictionaries and sets are treated as <code>False<\/code>.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Given this simple express.js middleware, what is its purpose?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-6\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> app.use(<span class=\"hljs-function\">(<span class=\"hljs-params\">req, res, next<\/span>) =><\/span> {\n res.setHeader(<span class=\"hljs-string\">'Cache-Control'<\/span>, <span class=\"hljs-string\">'no-cache'<\/span>);\n next();\n });<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-6\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This middleware sets the <code>Cache-Control<\/code> header to <code>no-cache<\/code> for all responses. It instructs the browser (or caching servers) not to cache the content of the response, ensuring that the client always fetches the latest content from the server.<\/p>\n\n\n\n<p><strong>Question:<\/strong> How can you ensure data integrity in a relational database? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Data integrity can be maintained through the use of constraints such as primary keys, foreign keys, unique constraints, and check constraints. Regular backups, validations, and normalization can also help maintain data integrity.<\/p>\n\n\n\n<p><strong>Question:<\/strong> In the following Node.js code, what issue might arise and how can you fix it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-7\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> <span class=\"hljs-keyword\">const<\/span> fs = <span class=\"hljs-built_in\">require<\/span>(<span class=\"hljs-string\">'fs'<\/span>);\n\n fs.readFile(<span class=\"hljs-string\">'file.txt'<\/span>, <span class=\"hljs-string\">'utf8'<\/span>, (err, data) => {\n <span class=\"hljs-keyword\">if<\/span> (err) <span class=\"hljs-keyword\">throw<\/span> err;\n <span class=\"hljs-built_in\">console<\/span>.log(data);\n });\n\n fs.unlinkSync(<span class=\"hljs-string\">'file.txt'<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-7\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The code is trying to read the content of ‘file.txt’ asynchronously while it’s being deleted synchronously. There’s a race condition; the file might be deleted before the readFile operation completes, leading to an error. To fix it, the deletion should be moved inside the callback of <code>readFile<\/code> to ensure the read operation completes before the file is deleted.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"intermediate-backend-developer-questions\">Intermediate backend developer questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> Describe the differences between horizontal and vertical scaling. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Horizontal scaling<\/strong> means adding more machines to a system. This is often referred to as scaling out. For example, adding more nodes to a distributed database or adding more servers in a load-balanced environment.<\/li>\n\n\n\n<li><strong>Vertical scaling<\/strong> means increasing the resources of an existing machine, such as adding more RAM, CPU, or storage. This is often referred to as scaling up.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Analyze the potential issues with this piece of code handling database connections:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-8\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def get_data(query):\n connection = create_db_connection()\n data = connection.execute(query)\n connection.close()\n <span class=\"hljs-keyword\">return<\/span> data<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-8\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> There are a couple potential issues:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>There’s no error handling. If the connection fails or the query has issues, the code could break.<\/li>\n\n\n\n<li>Each time data is fetched, a new database connection is established and closed. This is resource-intensive and can slow down applications, especially if <code>get_data<\/code> is called frequently.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> What are microservices, and what are their benefits over a monolithic architecture? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Microservices is an architectural style that structures an application as a collection of loosely coupled, independently deployable services. Each service corresponds to a business capability and often has its own database. Benefits include better scalability, flexibility in technology choices for each service, easier maintenance and upgrades, and enhanced fault isolation.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Examine the following endpoint in a Flask application and suggest improvements:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-9\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> @app.route(<span class=\"hljs-string\">'\/users\/<id>'<\/span>, methods=[<span class=\"hljs-string\">'GET'<\/span>])\n def get_user(id):\n user = db.session.query(User).filter_by(id=id).first()\n <span class=\"hljs-keyword\">return<\/span> jsonify(user)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-9\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The function doesn’t handle the case where the user might not be found, potentially leading to a <code>None<\/code> object being passed to <code>jsonify<\/code>. To fix this, Replace the function <code>first<\/code> by the function <code>one<\/code>. Exceptions will be raised and handled by the rest of the code if there is not exactly one record found.<\/li>\n\n\n\n<li>Directly serializing the ORM object may expose sensitive fields. It’s better to use a serialization method or library to ensure only required fields are exposed.<\/li>\n\n\n\n<li>No input validation or type checking for <code>id<\/code>.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> What is the potential bottleneck in the following database query?<\/p>\n\n\n<pre class=\"wp-block-code\"><span><code class=\"hljs shcb-wrap-lines\"> SELECT * FROM orders ORDER BY creation_date DESC LIMIT 10;<\/code><\/span><\/pre>\n\n\n<p><strong>Answer:<\/strong> If there is no index on the <code>creation_date<\/code> column, sorting the table can be resource-intensive, especially as the <code>orders<\/code> table grows in size. To improve this, an index on the <code>creation_date<\/code> column should be considered.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain the concept of eventual consistency. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Eventual consistency refers to a system state where all replicas of data might not be immediately consistent but will become consistent over time. It is a relaxation of the strong consistency model to achieve higher availability and scalability in distributed systems.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Consider the following asynchronous Node.js function. What’s wrong with it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-10\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> <span class=\"hljs-keyword\">async<\/span> <span class=\"hljs-function\"><span class=\"hljs-keyword\">function<\/span> <span class=\"hljs-title\">fetchData<\/span>(<span class=\"hljs-params\"><\/span>) <\/span>{\n <span class=\"hljs-keyword\">let<\/span> data = <span class=\"hljs-keyword\">await<\/span> someAsyncFunction();\n <span class=\"hljs-keyword\">if<\/span> (!data) {\n <span class=\"hljs-keyword\">throw<\/span> <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-built_in\">Error<\/span>(<span class=\"hljs-string\">\"Data not found\"<\/span>);\n }\n <span class=\"hljs-keyword\">return<\/span> processData(data);\n }<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-10\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function lacks error handling for potential failures of <code>someAsyncFunction()<\/code>. A try-catch block should be added around the <code>await<\/code> statement to handle any errors that might arise from that asynchronous call.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Look at this Redis caching function and identify any issues:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-11\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def cache_data(key, value):\n redis_client = redis.StrictRedis(host=<span class=\"hljs-string\">'localhost'<\/span>, port=<span class=\"hljs-number\">6379<\/span>, db=<span class=\"hljs-number\">0<\/span>)\n redis_client.set(key, value)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-11\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function initializes a new Redis connection each time it’s called. This can be inefficient, especially if caching operations are frequent. It’s better to maintain a persistent Redis connection or use a connection pool.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Analyze this Django ORM query for optimization:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-12\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> books = Book.objects.all()\n <span class=\"hljs-keyword\">for<\/span> book in books:\n <span class=\"hljs-keyword\">print<\/span>(book.author.name)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-12\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This code suffers from the “N+1 queries problem”. For each book, a separate query is made to fetch the author’s name, leading to N+1 queries in total (1 to fetch all books + N to fetch the authors). The optimized version would use <code>select_related<\/code>:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-13\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> books = Book.objects.select_related(<span class=\"hljs-string\">'author'<\/span>).all()\n <span class=\"hljs-keyword\">for<\/span> book in books:\n <span class=\"hljs-keyword\">print<\/span>(book.author.name)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-13\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Question:<\/strong> How does a message queue like RabbitMQ or Kafka improve system architecture?<\/p>\n\n\n\n<p><strong>Answer:<\/strong> Message queues decouple components in a system, allowing for asynchronous processing. This means that a component can send a message to the queue without waiting for it to be processed. This has several benefits:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Improved performance and responsiveness, as components don’t block waiting for tasks to complete.<\/li>\n\n\n\n<li>Enhanced system reliability, as the message queue can act as a buffer during high traffic or if a component fails and needs to restart.<\/li>\n\n\n\n<li>Better scalability, as workers can be easily added or removed based on the workload.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"senior-backend-developer-questions\">Senior backend developer questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> Explain the principles and benefits of the Twelve-Factor App methodology. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> The Twelve-Factor App is a set of best practices for building modern, scalable, maintainable software-as-a-service apps. Some key principles include:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Codebase<\/strong>: One codebase tracked in revision control, with many deploys.<\/li>\n\n\n\n<li><strong>Dependencies<\/strong>: Explicitly declare and isolate dependencies.<\/li>\n\n\n\n<li><strong>Config<\/strong>: Store configuration in the environment.<\/li>\n\n\n\n<li><strong>Backing Services<\/strong>: Treat backing services as attached resources.<\/li>\n\n\n\n<li><strong>Build, Release, Run<\/strong>: Strictly separate build and run stages.<\/li>\n\n\n\n<li><strong>Processes<\/strong>: Execute the app as one or more stateless processes.<\/li>\n\n\n\n<li><strong>Port Binding<\/strong>: Export services via port binding.<\/li>\n\n\n\n<li><strong>Concurrency<\/strong>: Scale out via the process model.<\/li>\n\n\n\n<li><strong>Disposability<\/strong>: Maximize robustness with fast startup and graceful shutdown.<\/li>\n\n\n\n<li><strong>Dev\/Prod Parity<\/strong>: Keep development, staging, and production as similar as possible.<\/li>\n\n\n\n<li><strong>Logs<\/strong>: Treat logs as event streams.<\/li>\n\n\n\n<li><strong>Admin Processes<\/strong>: Run admin\/management tasks as one-off processes.<\/li>\n<\/ol>\n\n\n\n<p>Benefits include portability across execution environments, minimized divergence between development and production, and scalability.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain the CAP theorem and its implications in distributed systems design. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><a href=\"https:\/\/en.wikipedia.org\/wiki\/CAP_theorem\" target=\"_blank\" rel=\"noopener\"> The CAP theorem<\/a> states that it’s impossible for a distributed system to simultaneously provide all three of the following guarantees:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Consistency<\/strong>: Every read receives the most recent write.<\/li>\n\n\n\n<li><strong>Availability<\/strong>: Every request receives a (non-error) response, without a guarantee that it contains the most recent version.<\/li>\n\n\n\n<li><strong>Partition tolerance<\/strong>: The system continues to operate despite arbitrary message loss or failure of part of the system.<\/li>\n<\/ul>\n\n\n\n<p>In the face of a network partition, a system must choose between consistency and availability. This theorem guides the design and trade-offs of distributed databases and systems.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Examine the following piece of Python code and identify potential issues related to concurrency:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-14\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> counter = <span class=\"hljs-number\">0<\/span>\n\n def increment_counter():\n <span class=\"hljs-keyword\">global<\/span> counter\n <span class=\"hljs-keyword\">for<\/span> _ in range(<span class=\"hljs-number\">1000000<\/span>):\n counter += <span class=\"hljs-number\">1<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-14\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> If <code>increment_counter<\/code> is called concurrently from multiple threads or processes, there could be race conditions leading to the <code>counter<\/code> not being accurately incremented. A synchronization mechanism like locks or semaphores should be employed to protect the critical section.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Given the following SQL query, how can it be optimized for a large dataset?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-15\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> SELECT orders.id, products.name \n FROM orders \n INNER JOIN products ON orders.product_id = products.id \n WHERE products.category = <span class=\"hljs-string\">'electronics'<\/span>;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-15\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Ensure there are indices on the columns involved in the JOIN operation (<code>orders.product_id<\/code> and <code>products.id<\/code>).<\/li>\n\n\n\n<li>Add an index on <code>products.category<\/code> since it’s used in the WHERE clause.<\/li>\n\n\n\n<li>Consider denormalization or materialized views if this is a frequently executed query.<\/li>\n\n\n\n<li>Think about reworking the database schema. The field <code>products.category<\/code> could be changed to a numeric field and the correspondance between num_category and str_category could be stored in an intermediate table.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Analyze this cache invalidation strategy and suggest improvements:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-16\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def update_product(product):\n db.save(product)\n cache.delete(f<span class=\"hljs-string\">'product-{product.id}'<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-16\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> While the function updates a product in the database and invalidates the cache, a race condition could occur where the cache is repopulated with old data before the database update completes. A better strategy might be to use cache versioning or to update the cache with the new data directly after the database update, ensuring fresh data is always available.<\/p>\n\n\n\n<p><strong>Question:<\/strong> How do you handle versioning in RESTful APIs? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> There are multiple strategies:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>URI Versioning<\/strong>: Include the version in the URI, e.g., <code>\/v1\/users<\/code>.<\/li>\n\n\n\n<li><strong>Header Versioning<\/strong>: Use custom headers, e.g., <code>Accept-version: v1<\/code>.<\/li>\n\n\n\n<li><strong>Accept Header<\/strong>: Use the <code>Accept<\/code> header with a versioned media type, e.g., <code>Accept: application\/json; Version=2<\/code>.<\/li>\n\n\n\n<li><strong>Query Parameter<\/strong>: Include the version in a query parameter, e.g., <code>\/users?version=1<\/code>.<\/li>\n<\/ul>\n\n\n\n<p>It’s essential to choose a method that aligns with the organization’s goals, and it’s also vital to provide proper documentation for clients.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Here’s a simplified code to manage tasks in a queue. Identify potential pitfalls:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-17\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> tasks = []\n\n def add_task(task):\n tasks.append(task)\n\n def process_next_task():\n <span class=\"hljs-keyword\">if<\/span> tasks:\n task = tasks.pop(<span class=\"hljs-number\">0<\/span>)\n <span class=\"hljs-comment\"># process task<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-17\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The list data structure in Python is not efficient for pop operations from the start of the list. This operation is O(n). Using a data structure like <code>deque<\/code> from the <code>collections<\/code> module would be more efficient.<\/li>\n\n\n\n<li>If used in a multithreaded environment, race conditions can occur, leading to tasks being processed multiple times or not at all. Proper synchronization or thread-safe collections should be used.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Consider the following Kafka consumer code snippet. What could be problematic about this?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-18\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> consumer = KafkaConsumer(<span class=\"hljs-string\">'my_topic'<\/span>)\n <span class=\"hljs-keyword\">for<\/span> message <span class=\"hljs-keyword\">in<\/span> consumer:\n process_message(message)\n consumer.commit()<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-18\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The consumer commits after processing each message, which can be inefficient and slow down the message processing rate. Depending on the <code>process_message<\/code> function, failures might result in message loss if a message is committed but not successfully processed. It might be better to batch the commits or use a commit strategy based on time or message count.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Describe the advantages and challenges of transitioning a monolithic application to a microservices architecture. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><br><em>Advantages<\/em>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><em>Scalability<\/em>: Each service can be scaled independently based on its requirements.<\/li>\n\n\n\n<li><em>Flexibility<\/em>: Different services can use different technologies.<\/li>\n\n\n\n<li><em>Maintainability<\/em>: Smaller codebases are easier to understand and maintain.<\/li>\n\n\n\n<li><em>Faster Time to Market<\/em>: Teams can work on different services simultaneously, leading to faster feature releases. <\/li>\n<\/ul>\n\n\n\n<p><em>Challenges<\/em>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><em>Network Complexity<\/em>: Increased inter-service communication can introduce latency and complexity.<\/li>\n\n\n\n<li><em>Data Consistency<\/em>: With services having their own databases, ensuring data consistency can be challenging.<\/li>\n\n\n\n<li><em>Operational Overhead<\/em>: More services mean more things to deploy, monitor, and manage.<\/li>\n\n\n\n<li><em>Service Discovery<\/em>: Services need to discover and communicate with each other.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"more-backend-interview-resources\">More backend interview resources<\/h2>\n\n\n\n<p>For more guides on improving your knowledge of software engineer hiring, we have outlined helpful blog posts below:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/coderpad.io\/blog\/hiring-developers\/hire-back-end-developers\/\">Hire Back-End Developers: 11 strategies and niche job boards<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/blog\/hiring-developers\/software-developers-want-to-leave-their-jobs-is-your-company-ready-to-recruit\/\">Software Developers Want to Leave Their Jobs. Is Your Company Ready to Recruit?<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/blog\/interviewing\/prompt-engineering-for-technical-interview-questions\/\">Prompt Engineering for Technical Interview Questions <\/a><\/li>\n<\/ul>\n\n\n\n<p>Additionally, we offer the following backend framework interview questions:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/nodejs-interview-questions\/\">Node.js<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/ruby-on-rails-interview-questions\/\">Ruby on Rails<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/django-interview-questions\/\">Django<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/spring-interview-questions\/\">Spring<\/a><\/li>\n<\/ul>\n\n\n\n<p><\/p>\n\n\n<section class=\"logo-row-block\">\n <div class=\"inner\">\n <h2 class=\"headline\">1,000 Companies use CoderPad to Screen and Interview Developers<\/h2>\n \n <div class=\"logos logos--grayscale\" >\n <div> <svg class=\"logo logo-spotify\" role=\"img\" viewBox=\"0 0 538 167\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><title>Spotify<\/title><path d=\"M83.743 0C37.494 0 0 37.493 0 83.742c0 46.251 37.494 83.741 83.743 83.741 46.254 0 83.744-37.49 83.744-83.741 0-46.246-37.49-83.738-83.745-83.738L83.743 0zm38.404 120.78a5.217 5.217 0 0 1-7.18 1.73c-19.662-12.01-44.414-14.73-73.564-8.07a5.222 5.222 0 0 1-6.249-3.93 5.213 5.213 0 0 1 3.926-6.25c31.9-7.288 59.263-4.15 81.337 9.34 2.46 1.51 3.24 4.72 1.73 7.18zm10.25-22.802c-1.89 3.072-5.91 4.042-8.98 2.152-22.51-13.836-56.823-17.843-83.448-9.761-3.453 1.043-7.1-.903-8.148-4.35a6.538 6.538 0 0 1 4.354-8.143c30.413-9.228 68.222-4.758 94.072 11.127 3.07 1.89 4.04 5.91 2.15 8.976v-.001zm.88-23.744c-26.99-16.031-71.52-17.505-97.289-9.684-4.138 1.255-8.514-1.081-9.768-5.219a7.835 7.835 0 0 1 5.221-9.771c29.581-8.98 78.756-7.245 109.83 11.202a7.823 7.823 0 0 1 2.74 10.733c-2.2 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id=\"chartboost-a\"><path fill=\"currentColor\" d=\"M.158.5h205v30h-205z\"\/><\/clipPath><\/defs><\/svg>\n\n<\/div>\n <\/div>\n <\/div>\n<\/section>\n\n\n\n<div class=\"wp-block-columns\">\n<div class=\"wp-block-column\"><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img decoding=\"async\" src=\"https:\/\/d2h1bfu6zrdxog.cloudfront.net\/wp-content\/uploads\/2023\/03\/g2-leader-winter-2023.png\" alt=\"\" class=\"wp-image-32119\"\/><\/figure>\n<\/div><\/div>\n\n\n\n<div class=\"wp-block-column\"><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img decoding=\"async\" src=\"https:\/\/d2h1bfu6zrdxog.cloudfront.net\/wp-content\/uploads\/2023\/03\/g2-users-love-us.png\" alt=\"\" class=\"wp-image-32120\"\/><\/figure>\n<\/div><\/div>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"best-interview-practices-for-backend-roles\">Best interview practices for backend roles<\/h2>\n\n\n\n<p>The backend interview process can often be quite diverse, influenced by various elements including the specific engineering role in focus and the applicant’s level of expertise in backend technologies. To enhance the effectiveness of your backend interview questions, consider adopting the following strategies when interacting with potential recruits:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Develop technical queries that reflect actual scenarios encountered in your organization – this approach is not only more engaging for the candidate but also serves as a more accurate gauge of how their skill set aligns with your team’s needs.<\/li>\n\n\n\n<li>Encourage a participatory environment by allowing the candidate to pose questions throughout the process.<\/li>\n\n\n\n<li>Given that backend candidates may sometimes need to collaborate with front-end teams, it is advantageous for them to have a foundational understanding of the principles that govern user interface and user experience design.<\/li>\n<\/ul>\n\n\n\n<p>Furthermore, adhering to standard interview protocols remains crucial during backend interview sessions – adjust the complexity of interview questions based on the candidate’s evolving expertise, provide timely feedback regarding their status in the recruitment process, and offer sufficient opportunities for candidates to discuss the evaluation or delve into the nuances of collaborating with your team.<\/p>\n","protected":false},"parent":0,"menu_order":0,"template":"","class_list":["post-36441","interview-questions","type-interview-questions","status-publish","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/interview-questions\/36441","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/interview-questions"}],"about":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/types\/interview-questions"}],"wp:attachment":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/media?parent=36441"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
According to the CoderPad 2024 Developer survey<\/a>, backend developers are the the second-most in-demand job role technical recruiters are looking to fill.<\/p>\n<\/blockquote>\n\n\n\nIn the subsequent sections, you will find an array of practical coding tasks and interview questions designed to assess the technical competence of backend developer candidates during evaluations.<\/p>\n\n\n\nAdditionally, we have included a selection of endorsed best practices to aid in a reliable assessment of candidates’ backend skills through your interview queries.<\/p>\n\n\n\nTable of Contents<\/h2>Backend example questions<\/a>Question 1: Create a CRUD API<\/a><\/ul><\/li>Question 2: Shopping List<\/a><\/ul><\/li><\/ul><\/li>Junior backend interview questions<\/a><\/li>Intermediate backend developer questions<\/a><\/li>Senior backend developer questions<\/a><\/li>More backend interview resources<\/a><\/li>Best interview practices for backend roles<\/a><\/li><\/ul><\/nav><\/div>\n\n\n\nBackend<\/strong> example questions<\/strong><\/h2>\n\n\n\nQuestion 1: Create a CRUD API<\/strong><\/h3>\n\n\n\nThe goal of this exercise is to retrieve data from an external source, store it in an appropriate database structure, and create a CRUD RESTful API to interface with the database<\/p>\n\n\n\nGoals<\/h4>\n\n\n\n1. Read the data from this graphql endpoint: https:\/\/swapi-graphql.netlify.app\/.netlify\/functions\/index<\/a> with the following query:<\/p>\n\n\n\nquery Query {allPlanets{planets{name population terrains climates}}}<\/code><\/p>\n\n\n\n(View the shape of the data here<\/a>.)<\/p>\n\n\n\n2. Store the data from the graphql endpoint into the database and create appropriate models<\/p>\n\n\n\n3. Write RESTful Create, Read, Update, and Delete endpoints to interact with the database<\/p>\n\n\n\n\t<\/iframe>\n<\/div>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"question-2-shopping-list\"><strong>Question 2: Shopping List<\/strong><\/h3>\n\n\n\n<p>This question tests a candidate’s ability to create model(s) for the data structure, insert hard-coded data into a database, modify tables and fields in a database, and write endpoints to interact with data.<\/p>\n\n\n\n<p><strong>Part 1<\/strong><\/p>\n\n\n\n<p><em>Create a model for the shopping lists and items located in app\/data\/data.ts.<\/em><\/p>\n\n\n\n<p><strong>Part 2<\/strong><\/p>\n\n\n\n<p><em>Store the shopping lists and items located in app\/data\/data.ts in the database.<\/em><\/p>\n\n\n\n<p><strong>Part 3<\/strong><\/p>\n\n\n\n<p><em>Modify the database such that a price field can be stored for each item.<\/em><\/p>\n\n\n\n<p><strong>Part 4<\/strong><\/p>\n\n\n\n<p><em>Multiply the quantity of each item in the shopping lists by two.<\/em><\/p>\n\n\n\n<p><strong>Part 5<\/strong><\/p>\n\n\n\n<p><em>Create API endpoints to dynamically get a list of shopping lists and items.<\/em><\/p>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"assessing-the-candidate\"><strong>Assessing the candidate<\/strong><\/h4>\n\n\n\n<p>The candidate should create models for a shopping list and items. They should then write code to create the tables necessary and insert the data into the tables. Additionally, the candidate can be asked to edit the data in the tables and add additional fields. Finally, endpoints to interact with the data can be created.<\/p>\n\n\n<div\n\tclass=\"sandbox-embed responsive-embed sandbox-embed--full-width\"\n\tstyle=\"padding-top: 85%\"\ndata-block-name=\"coderpad-sandbox-embed\">\n\t<iframe src=\"https:\/\/embed.coderpad.io\/sandbox?question_id=254803u0026use_question_button\" width=\"640\" height=\"544\" loading=\"lazy\" aria-label=\"Try out the CoderPad sandbox\"><\/iframe>\n<\/div>\n\n\n<section class=\"\n\ticon-lists-block\n\t\n\" data-block-name=\"coderpad-icon-lists-block\">\n <div class=\"inner\">\n\n \n <div class=\"lists lists--2\">\n <div class=\"icon-list\">\n <div class=\"top\">\n <div class=\"icon-container\">\n <svg class=\"icon icon-lightning-bolt\" role=\"img\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" fill=\"none\" viewBox=\"0 0 10 14\"><title>lightning bolt<\/title><path fill=\"currentColor\" d=\"M3.608 13.967c.185.079.4.013.508-.158l4.922-7.82a.41.41 0 0 0-.347-.63H5.407L6.628.511a.41.41 0 0 0-.744-.32L.962 8.011a.41.41 0 0 0 .347.63h3.284l-1.221 4.848a.41.41 0 0 0 .236.478Z\"\/><\/svg>\n\n <\/div>\n \n <h3 class=\"title\">Backend skills to assess<\/h3>\n <\/div>\n\n <ul class=\"links\">\n <li>\n <a >Backend frameworks<\/a>\n <\/li>\n <li>\n <a >RESTful API design<\/a>\n <\/li>\n <li>\n <a >Databases and ORMs<\/a>\n <\/li>\n <\/ul>\n <\/div>\n\n <div class=\"icon-list\">\n <div class=\"top\">\n <div class=\"icon-container\">\n <svg class=\"icon icon-briefcase\" role=\"img\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" viewBox=\"0 0 25 26\" fill=\"none\"><title>briefcase<\/title><path fill=\"currentColor\" d=\"M5.469 16.125a5.446 5.446 0 0 1-3.907-1.648v6.335a2.35 2.35 0 0 0 2.344 2.344h17.188a2.35 2.35 0 0 0 2.343-2.343v-6.336a5.446 5.446 0 0 1-3.906 1.648H5.47Z\"\/><path fill=\"currentColor\" d=\"M21.094 5.969h-3.125v-.782a2.344 2.344 0 0 0-2.344-2.343h-6.25a2.344 2.344 0 0 0-2.344 2.344v.78H3.906a2.35 2.35 0 0 0-2.344 2.345v2.343a3.906 3.906 0 0 0 3.907 3.906h2.343V12.22a.781.781 0 1 1 1.563 0v2.344h6.25v-2.344a.781.781 0 1 1 1.563 0v2.344h2.343a3.907 3.907 0 0 0 3.907-3.907V8.312a2.351 2.351 0 0 0-2.344-2.343Zm-12.5-.782a.781.781 0 0 1 .781-.78h6.25a.781.781 0 0 1 .781.78v.782H8.594v-.782Z\"\/><\/svg>\n\n <\/div>\n \n <h3 class=\"title\">Backend job roles<\/h3>\n <\/div>\n\n <ul class=\"links\">\n <li>\n <a >Backend developer<\/a>\n <\/li>\n <li>\n <a >Software engineer<\/a>\n <\/li>\n <li>\n <a >Full-stack developer<\/a>\n <\/li>\n <\/ul>\n <\/div>\n\n <\/div>\n \n <\/div>\n<\/section>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"junior-backend-interview-questions\">Junior backend interview questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> What’s the difference between a framework and a library? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> A library is a collection of functions\/methods\/classes that you can call from your own code. You’re in charge of the flow of the application; you decide when to call the library. In contrast, with a framework, the flow is determined by the framework itself, invoking your code at specific points (Inversion of Control). Examples include Flask as a framework and NumPy as a library in Python.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Consider the following Python code snippet. Can you identify what’s wrong with it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def add_numbers(a, b):\n <span class=\"hljs-keyword\">return<\/span> a + b\n\n result = add_numbers(<span class=\"hljs-string\">\"5\"<\/span>, <span class=\"hljs-number\">3<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function <code>add_numbers<\/code> is trying to add a string (“5”) and an integer (3) together, which will raise a TypeError in Python. To fix it, one must ensure that both variables are of the same datatype, by converting the string to an integer.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain what a <code>JOIN<\/code> operation is in SQL. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> A <code>JOIN<\/code> operation in SQL is used to combine rows from two or more tables based on a related column between them. The most common types of JOINs include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Look at this SQL query and explain if there is any vulnerability:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> query = <span class=\"hljs-string\">\"SELECT * FROM users WHERE username = '\"<\/span> + username + <span class=\"hljs-string\">\"' AND password = '\"<\/span> + password + <span class=\"hljs-string\">\"';\"<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This query is vulnerable to SQL injection. An attacker can provide malicious input in <code>username<\/code> or <code>password<\/code> to modify the query and potentially access or harm the database. To prevent this, one should use parameterized queries or prepared statements.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Describe the concept of statelessness in RESTful APIs. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Statelessness means that each HTTP request from a client to a server must contain all the information needed to understand and process the request. The server should not store any context between requests, ensuring that each request can be understood in isolation.<\/p>\n\n\n\n<p><strong>Question:<\/strong> What’s the output of the following Python function?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> def mystery_function(a, b=[]):\n b.append(a)\n <span class=\"hljs-keyword\">return<\/span> b\n\n <span class=\"hljs-keyword\">print<\/span>(mystery_function(<span class=\"hljs-number\">1<\/span>))\n <span class=\"hljs-keyword\">print<\/span>(mystery_function(<span class=\"hljs-number\">2<\/span>))<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The output will be:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"JSON \/ JSON with Comments\" data-shcb-language-slug=\"json\"><span><code class=\"hljs language-json shcb-wrap-lines\"> [<span class=\"hljs-number\">1<\/span>]\n [<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">2<\/span>]<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JSON \/ JSON with Comments<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">json<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The mutable default argument (<code>b=[]<\/code>) is a common Python gotcha. The list <code>b<\/code> is created only once when the function is defined, so successive calls to the function reuse the same list.<\/p>\n\n\n\n<p><strong>Question:<\/strong> What is the most Pythonic way to check if a list is empty (considering you are sure the variable to test is a list) ?<\/p>\n\n\n\n<p><strong>Answer:<\/strong> <\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"><span class=\"hljs-keyword\">if<\/span> my_list:\n <span class=\"hljs-comment\"># do something when list is not empty<\/span>\n<span class=\"hljs-keyword\">else<\/span>:\n <span class=\"hljs-comment\"># do something when list is empty<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>It is not necessary to compare it with <code>== []<\/code> or to call <code>len(my_list)<\/code>. When used in a condition, the empty tuples, lists, dictionaries and sets are treated as <code>False<\/code>.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Given this simple express.js middleware, what is its purpose?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-6\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> app.use(<span class=\"hljs-function\">(<span class=\"hljs-params\">req, res, next<\/span>) =><\/span> {\n res.setHeader(<span class=\"hljs-string\">'Cache-Control'<\/span>, <span class=\"hljs-string\">'no-cache'<\/span>);\n next();\n });<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-6\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This middleware sets the <code>Cache-Control<\/code> header to <code>no-cache<\/code> for all responses. It instructs the browser (or caching servers) not to cache the content of the response, ensuring that the client always fetches the latest content from the server.<\/p>\n\n\n\n<p><strong>Question:<\/strong> How can you ensure data integrity in a relational database? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Data integrity can be maintained through the use of constraints such as primary keys, foreign keys, unique constraints, and check constraints. Regular backups, validations, and normalization can also help maintain data integrity.<\/p>\n\n\n\n<p><strong>Question:<\/strong> In the following Node.js code, what issue might arise and how can you fix it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-7\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> <span class=\"hljs-keyword\">const<\/span> fs = <span class=\"hljs-built_in\">require<\/span>(<span class=\"hljs-string\">'fs'<\/span>);\n\n fs.readFile(<span class=\"hljs-string\">'file.txt'<\/span>, <span class=\"hljs-string\">'utf8'<\/span>, (err, data) => {\n <span class=\"hljs-keyword\">if<\/span> (err) <span class=\"hljs-keyword\">throw<\/span> err;\n <span class=\"hljs-built_in\">console<\/span>.log(data);\n });\n\n fs.unlinkSync(<span class=\"hljs-string\">'file.txt'<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-7\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The code is trying to read the content of ‘file.txt’ asynchronously while it’s being deleted synchronously. There’s a race condition; the file might be deleted before the readFile operation completes, leading to an error. To fix it, the deletion should be moved inside the callback of <code>readFile<\/code> to ensure the read operation completes before the file is deleted.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"intermediate-backend-developer-questions\">Intermediate backend developer questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> Describe the differences between horizontal and vertical scaling. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Horizontal scaling<\/strong> means adding more machines to a system. This is often referred to as scaling out. For example, adding more nodes to a distributed database or adding more servers in a load-balanced environment.<\/li>\n\n\n\n<li><strong>Vertical scaling<\/strong> means increasing the resources of an existing machine, such as adding more RAM, CPU, or storage. This is often referred to as scaling up.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Analyze the potential issues with this piece of code handling database connections:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-8\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def get_data(query):\n connection = create_db_connection()\n data = connection.execute(query)\n connection.close()\n <span class=\"hljs-keyword\">return<\/span> data<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-8\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> There are a couple potential issues:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>There’s no error handling. If the connection fails or the query has issues, the code could break.<\/li>\n\n\n\n<li>Each time data is fetched, a new database connection is established and closed. This is resource-intensive and can slow down applications, especially if <code>get_data<\/code> is called frequently.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> What are microservices, and what are their benefits over a monolithic architecture? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Microservices is an architectural style that structures an application as a collection of loosely coupled, independently deployable services. Each service corresponds to a business capability and often has its own database. Benefits include better scalability, flexibility in technology choices for each service, easier maintenance and upgrades, and enhanced fault isolation.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Examine the following endpoint in a Flask application and suggest improvements:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-9\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> @app.route(<span class=\"hljs-string\">'\/users\/<id>'<\/span>, methods=[<span class=\"hljs-string\">'GET'<\/span>])\n def get_user(id):\n user = db.session.query(User).filter_by(id=id).first()\n <span class=\"hljs-keyword\">return<\/span> jsonify(user)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-9\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The function doesn’t handle the case where the user might not be found, potentially leading to a <code>None<\/code> object being passed to <code>jsonify<\/code>. To fix this, Replace the function <code>first<\/code> by the function <code>one<\/code>. Exceptions will be raised and handled by the rest of the code if there is not exactly one record found.<\/li>\n\n\n\n<li>Directly serializing the ORM object may expose sensitive fields. It’s better to use a serialization method or library to ensure only required fields are exposed.<\/li>\n\n\n\n<li>No input validation or type checking for <code>id<\/code>.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> What is the potential bottleneck in the following database query?<\/p>\n\n\n<pre class=\"wp-block-code\"><span><code class=\"hljs shcb-wrap-lines\"> SELECT * FROM orders ORDER BY creation_date DESC LIMIT 10;<\/code><\/span><\/pre>\n\n\n<p><strong>Answer:<\/strong> If there is no index on the <code>creation_date<\/code> column, sorting the table can be resource-intensive, especially as the <code>orders<\/code> table grows in size. To improve this, an index on the <code>creation_date<\/code> column should be considered.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain the concept of eventual consistency. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Eventual consistency refers to a system state where all replicas of data might not be immediately consistent but will become consistent over time. It is a relaxation of the strong consistency model to achieve higher availability and scalability in distributed systems.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Consider the following asynchronous Node.js function. What’s wrong with it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-10\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> <span class=\"hljs-keyword\">async<\/span> <span class=\"hljs-function\"><span class=\"hljs-keyword\">function<\/span> <span class=\"hljs-title\">fetchData<\/span>(<span class=\"hljs-params\"><\/span>) <\/span>{\n <span class=\"hljs-keyword\">let<\/span> data = <span class=\"hljs-keyword\">await<\/span> someAsyncFunction();\n <span class=\"hljs-keyword\">if<\/span> (!data) {\n <span class=\"hljs-keyword\">throw<\/span> <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-built_in\">Error<\/span>(<span class=\"hljs-string\">\"Data not found\"<\/span>);\n }\n <span class=\"hljs-keyword\">return<\/span> processData(data);\n }<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-10\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function lacks error handling for potential failures of <code>someAsyncFunction()<\/code>. A try-catch block should be added around the <code>await<\/code> statement to handle any errors that might arise from that asynchronous call.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Look at this Redis caching function and identify any issues:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-11\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def cache_data(key, value):\n redis_client = redis.StrictRedis(host=<span class=\"hljs-string\">'localhost'<\/span>, port=<span class=\"hljs-number\">6379<\/span>, db=<span class=\"hljs-number\">0<\/span>)\n redis_client.set(key, value)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-11\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function initializes a new Redis connection each time it’s called. This can be inefficient, especially if caching operations are frequent. It’s better to maintain a persistent Redis connection or use a connection pool.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Analyze this Django ORM query for optimization:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-12\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> books = Book.objects.all()\n <span class=\"hljs-keyword\">for<\/span> book in books:\n <span class=\"hljs-keyword\">print<\/span>(book.author.name)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-12\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This code suffers from the “N+1 queries problem”. For each book, a separate query is made to fetch the author’s name, leading to N+1 queries in total (1 to fetch all books + N to fetch the authors). The optimized version would use <code>select_related<\/code>:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-13\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> books = Book.objects.select_related(<span class=\"hljs-string\">'author'<\/span>).all()\n <span class=\"hljs-keyword\">for<\/span> book in books:\n <span class=\"hljs-keyword\">print<\/span>(book.author.name)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-13\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Question:<\/strong> How does a message queue like RabbitMQ or Kafka improve system architecture?<\/p>\n\n\n\n<p><strong>Answer:<\/strong> Message queues decouple components in a system, allowing for asynchronous processing. This means that a component can send a message to the queue without waiting for it to be processed. This has several benefits:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Improved performance and responsiveness, as components don’t block waiting for tasks to complete.<\/li>\n\n\n\n<li>Enhanced system reliability, as the message queue can act as a buffer during high traffic or if a component fails and needs to restart.<\/li>\n\n\n\n<li>Better scalability, as workers can be easily added or removed based on the workload.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"senior-backend-developer-questions\">Senior backend developer questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> Explain the principles and benefits of the Twelve-Factor App methodology. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> The Twelve-Factor App is a set of best practices for building modern, scalable, maintainable software-as-a-service apps. Some key principles include:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Codebase<\/strong>: One codebase tracked in revision control, with many deploys.<\/li>\n\n\n\n<li><strong>Dependencies<\/strong>: Explicitly declare and isolate dependencies.<\/li>\n\n\n\n<li><strong>Config<\/strong>: Store configuration in the environment.<\/li>\n\n\n\n<li><strong>Backing Services<\/strong>: Treat backing services as attached resources.<\/li>\n\n\n\n<li><strong>Build, Release, Run<\/strong>: Strictly separate build and run stages.<\/li>\n\n\n\n<li><strong>Processes<\/strong>: Execute the app as one or more stateless processes.<\/li>\n\n\n\n<li><strong>Port Binding<\/strong>: Export services via port binding.<\/li>\n\n\n\n<li><strong>Concurrency<\/strong>: Scale out via the process model.<\/li>\n\n\n\n<li><strong>Disposability<\/strong>: Maximize robustness with fast startup and graceful shutdown.<\/li>\n\n\n\n<li><strong>Dev\/Prod Parity<\/strong>: Keep development, staging, and production as similar as possible.<\/li>\n\n\n\n<li><strong>Logs<\/strong>: Treat logs as event streams.<\/li>\n\n\n\n<li><strong>Admin Processes<\/strong>: Run admin\/management tasks as one-off processes.<\/li>\n<\/ol>\n\n\n\n<p>Benefits include portability across execution environments, minimized divergence between development and production, and scalability.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain the CAP theorem and its implications in distributed systems design. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><a href=\"https:\/\/en.wikipedia.org\/wiki\/CAP_theorem\" target=\"_blank\" rel=\"noopener\"> The CAP theorem<\/a> states that it’s impossible for a distributed system to simultaneously provide all three of the following guarantees:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Consistency<\/strong>: Every read receives the most recent write.<\/li>\n\n\n\n<li><strong>Availability<\/strong>: Every request receives a (non-error) response, without a guarantee that it contains the most recent version.<\/li>\n\n\n\n<li><strong>Partition tolerance<\/strong>: The system continues to operate despite arbitrary message loss or failure of part of the system.<\/li>\n<\/ul>\n\n\n\n<p>In the face of a network partition, a system must choose between consistency and availability. This theorem guides the design and trade-offs of distributed databases and systems.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Examine the following piece of Python code and identify potential issues related to concurrency:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-14\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> counter = <span class=\"hljs-number\">0<\/span>\n\n def increment_counter():\n <span class=\"hljs-keyword\">global<\/span> counter\n <span class=\"hljs-keyword\">for<\/span> _ in range(<span class=\"hljs-number\">1000000<\/span>):\n counter += <span class=\"hljs-number\">1<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-14\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> If <code>increment_counter<\/code> is called concurrently from multiple threads or processes, there could be race conditions leading to the <code>counter<\/code> not being accurately incremented. A synchronization mechanism like locks or semaphores should be employed to protect the critical section.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Given the following SQL query, how can it be optimized for a large dataset?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-15\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> SELECT orders.id, products.name \n FROM orders \n INNER JOIN products ON orders.product_id = products.id \n WHERE products.category = <span class=\"hljs-string\">'electronics'<\/span>;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-15\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Ensure there are indices on the columns involved in the JOIN operation (<code>orders.product_id<\/code> and <code>products.id<\/code>).<\/li>\n\n\n\n<li>Add an index on <code>products.category<\/code> since it’s used in the WHERE clause.<\/li>\n\n\n\n<li>Consider denormalization or materialized views if this is a frequently executed query.<\/li>\n\n\n\n<li>Think about reworking the database schema. The field <code>products.category<\/code> could be changed to a numeric field and the correspondance between num_category and str_category could be stored in an intermediate table.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Analyze this cache invalidation strategy and suggest improvements:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-16\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def update_product(product):\n db.save(product)\n cache.delete(f<span class=\"hljs-string\">'product-{product.id}'<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-16\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> While the function updates a product in the database and invalidates the cache, a race condition could occur where the cache is repopulated with old data before the database update completes. A better strategy might be to use cache versioning or to update the cache with the new data directly after the database update, ensuring fresh data is always available.<\/p>\n\n\n\n<p><strong>Question:<\/strong> How do you handle versioning in RESTful APIs? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> There are multiple strategies:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>URI Versioning<\/strong>: Include the version in the URI, e.g., <code>\/v1\/users<\/code>.<\/li>\n\n\n\n<li><strong>Header Versioning<\/strong>: Use custom headers, e.g., <code>Accept-version: v1<\/code>.<\/li>\n\n\n\n<li><strong>Accept Header<\/strong>: Use the <code>Accept<\/code> header with a versioned media type, e.g., <code>Accept: application\/json; Version=2<\/code>.<\/li>\n\n\n\n<li><strong>Query Parameter<\/strong>: Include the version in a query parameter, e.g., <code>\/users?version=1<\/code>.<\/li>\n<\/ul>\n\n\n\n<p>It’s essential to choose a method that aligns with the organization’s goals, and it’s also vital to provide proper documentation for clients.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Here’s a simplified code to manage tasks in a queue. Identify potential pitfalls:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-17\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> tasks = []\n\n def add_task(task):\n tasks.append(task)\n\n def process_next_task():\n <span class=\"hljs-keyword\">if<\/span> tasks:\n task = tasks.pop(<span class=\"hljs-number\">0<\/span>)\n <span class=\"hljs-comment\"># process task<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-17\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The list data structure in Python is not efficient for pop operations from the start of the list. This operation is O(n). Using a data structure like <code>deque<\/code> from the <code>collections<\/code> module would be more efficient.<\/li>\n\n\n\n<li>If used in a multithreaded environment, race conditions can occur, leading to tasks being processed multiple times or not at all. Proper synchronization or thread-safe collections should be used.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Consider the following Kafka consumer code snippet. What could be problematic about this?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-18\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> consumer = KafkaConsumer(<span class=\"hljs-string\">'my_topic'<\/span>)\n <span class=\"hljs-keyword\">for<\/span> message <span class=\"hljs-keyword\">in<\/span> consumer:\n process_message(message)\n consumer.commit()<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-18\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The consumer commits after processing each message, which can be inefficient and slow down the message processing rate. Depending on the <code>process_message<\/code> function, failures might result in message loss if a message is committed but not successfully processed. It might be better to batch the commits or use a commit strategy based on time or message count.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Describe the advantages and challenges of transitioning a monolithic application to a microservices architecture. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><br><em>Advantages<\/em>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><em>Scalability<\/em>: Each service can be scaled independently based on its requirements.<\/li>\n\n\n\n<li><em>Flexibility<\/em>: Different services can use different technologies.<\/li>\n\n\n\n<li><em>Maintainability<\/em>: Smaller codebases are easier to understand and maintain.<\/li>\n\n\n\n<li><em>Faster Time to Market<\/em>: Teams can work on different services simultaneously, leading to faster feature releases. <\/li>\n<\/ul>\n\n\n\n<p><em>Challenges<\/em>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><em>Network Complexity<\/em>: Increased inter-service communication can introduce latency and complexity.<\/li>\n\n\n\n<li><em>Data Consistency<\/em>: With services having their own databases, ensuring data consistency can be challenging.<\/li>\n\n\n\n<li><em>Operational Overhead<\/em>: More services mean more things to deploy, monitor, and manage.<\/li>\n\n\n\n<li><em>Service Discovery<\/em>: Services need to discover and communicate with each other.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"more-backend-interview-resources\">More backend interview resources<\/h2>\n\n\n\n<p>For more guides on improving your knowledge of software engineer hiring, we have outlined helpful blog posts below:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/coderpad.io\/blog\/hiring-developers\/hire-back-end-developers\/\">Hire Back-End Developers: 11 strategies and niche job boards<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/blog\/hiring-developers\/software-developers-want-to-leave-their-jobs-is-your-company-ready-to-recruit\/\">Software Developers Want to Leave Their Jobs. Is Your Company Ready to Recruit?<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/blog\/interviewing\/prompt-engineering-for-technical-interview-questions\/\">Prompt Engineering for Technical Interview Questions <\/a><\/li>\n<\/ul>\n\n\n\n<p>Additionally, we offer the following backend framework interview questions:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/nodejs-interview-questions\/\">Node.js<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/ruby-on-rails-interview-questions\/\">Ruby on Rails<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/django-interview-questions\/\">Django<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/spring-interview-questions\/\">Spring<\/a><\/li>\n<\/ul>\n\n\n\n<p><\/p>\n\n\n<section class=\"logo-row-block\">\n <div class=\"inner\">\n <h2 class=\"headline\">1,000 Companies use CoderPad to Screen and Interview 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id=\"chartboost-a\"><path fill=\"currentColor\" d=\"M.158.5h205v30h-205z\"\/><\/clipPath><\/defs><\/svg>\n\n<\/div>\n <\/div>\n <\/div>\n<\/section>\n\n\n\n<div class=\"wp-block-columns\">\n<div class=\"wp-block-column\"><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img decoding=\"async\" src=\"https:\/\/d2h1bfu6zrdxog.cloudfront.net\/wp-content\/uploads\/2023\/03\/g2-leader-winter-2023.png\" alt=\"\" class=\"wp-image-32119\"\/><\/figure>\n<\/div><\/div>\n\n\n\n<div class=\"wp-block-column\"><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img decoding=\"async\" src=\"https:\/\/d2h1bfu6zrdxog.cloudfront.net\/wp-content\/uploads\/2023\/03\/g2-users-love-us.png\" alt=\"\" class=\"wp-image-32120\"\/><\/figure>\n<\/div><\/div>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"best-interview-practices-for-backend-roles\">Best interview practices for backend roles<\/h2>\n\n\n\n<p>The backend interview process can often be quite diverse, influenced by various elements including the specific engineering role in focus and the applicant’s level of expertise in backend technologies. To enhance the effectiveness of your backend interview questions, consider adopting the following strategies when interacting with potential recruits:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Develop technical queries that reflect actual scenarios encountered in your organization – this approach is not only more engaging for the candidate but also serves as a more accurate gauge of how their skill set aligns with your team’s needs.<\/li>\n\n\n\n<li>Encourage a participatory environment by allowing the candidate to pose questions throughout the process.<\/li>\n\n\n\n<li>Given that backend candidates may sometimes need to collaborate with front-end teams, it is advantageous for them to have a foundational understanding of the principles that govern user interface and user experience design.<\/li>\n<\/ul>\n\n\n\n<p>Furthermore, adhering to standard interview protocols remains crucial during backend interview sessions – adjust the complexity of interview questions based on the candidate’s evolving expertise, provide timely feedback regarding their status in the recruitment process, and offer sufficient opportunities for candidates to discuss the evaluation or delve into the nuances of collaborating with your team.<\/p>\n","protected":false},"parent":0,"menu_order":0,"template":"","class_list":["post-36441","interview-questions","type-interview-questions","status-publish","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/interview-questions\/36441","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/interview-questions"}],"about":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/types\/interview-questions"}],"wp:attachment":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/media?parent=36441"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
In the subsequent sections, you will find an array of practical coding tasks and interview questions designed to assess the technical competence of backend developer candidates during evaluations.<\/p>\n\n\n\n
Additionally, we have included a selection of endorsed best practices to aid in a reliable assessment of candidates’ backend skills through your interview queries.<\/p>\n\n\n\n
The goal of this exercise is to retrieve data from an external source, store it in an appropriate database structure, and create a CRUD RESTful API to interface with the database<\/p>\n\n\n\n
1. Read the data from this graphql endpoint: https:\/\/swapi-graphql.netlify.app\/.netlify\/functions\/index<\/a> with the following query:<\/p>\n\n\n\nquery Query {allPlanets{planets{name population terrains climates}}}<\/code><\/p>\n\n\n\n(View the shape of the data here<\/a>.)<\/p>\n\n\n\n2. Store the data from the graphql endpoint into the database and create appropriate models<\/p>\n\n\n\n3. Write RESTful Create, Read, Update, and Delete endpoints to interact with the database<\/p>\n\n\n\n\t<\/iframe>\n<\/div>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"question-2-shopping-list\"><strong>Question 2: Shopping List<\/strong><\/h3>\n\n\n\n<p>This question tests a candidate’s ability to create model(s) for the data structure, insert hard-coded data into a database, modify tables and fields in a database, and write endpoints to interact with data.<\/p>\n\n\n\n<p><strong>Part 1<\/strong><\/p>\n\n\n\n<p><em>Create a model for the shopping lists and items located in app\/data\/data.ts.<\/em><\/p>\n\n\n\n<p><strong>Part 2<\/strong><\/p>\n\n\n\n<p><em>Store the shopping lists and items located in app\/data\/data.ts in the database.<\/em><\/p>\n\n\n\n<p><strong>Part 3<\/strong><\/p>\n\n\n\n<p><em>Modify the database such that a price field can be stored for each item.<\/em><\/p>\n\n\n\n<p><strong>Part 4<\/strong><\/p>\n\n\n\n<p><em>Multiply the quantity of each item in the shopping lists by two.<\/em><\/p>\n\n\n\n<p><strong>Part 5<\/strong><\/p>\n\n\n\n<p><em>Create API endpoints to dynamically get a list of shopping lists and items.<\/em><\/p>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"assessing-the-candidate\"><strong>Assessing the candidate<\/strong><\/h4>\n\n\n\n<p>The candidate should create models for a shopping list and items. They should then write code to create the tables necessary and insert the data into the tables. Additionally, the candidate can be asked to edit the data in the tables and add additional fields. Finally, endpoints to interact with the data can be created.<\/p>\n\n\n<div\n\tclass=\"sandbox-embed responsive-embed sandbox-embed--full-width\"\n\tstyle=\"padding-top: 85%\"\ndata-block-name=\"coderpad-sandbox-embed\">\n\t<iframe src=\"https:\/\/embed.coderpad.io\/sandbox?question_id=254803u0026use_question_button\" width=\"640\" height=\"544\" loading=\"lazy\" aria-label=\"Try out the CoderPad sandbox\"><\/iframe>\n<\/div>\n\n\n<section class=\"\n\ticon-lists-block\n\t\n\" data-block-name=\"coderpad-icon-lists-block\">\n <div class=\"inner\">\n\n \n <div class=\"lists lists--2\">\n <div class=\"icon-list\">\n <div class=\"top\">\n <div class=\"icon-container\">\n <svg class=\"icon icon-lightning-bolt\" role=\"img\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" fill=\"none\" viewBox=\"0 0 10 14\"><title>lightning bolt<\/title><path fill=\"currentColor\" d=\"M3.608 13.967c.185.079.4.013.508-.158l4.922-7.82a.41.41 0 0 0-.347-.63H5.407L6.628.511a.41.41 0 0 0-.744-.32L.962 8.011a.41.41 0 0 0 .347.63h3.284l-1.221 4.848a.41.41 0 0 0 .236.478Z\"\/><\/svg>\n\n <\/div>\n \n <h3 class=\"title\">Backend skills to assess<\/h3>\n <\/div>\n\n <ul class=\"links\">\n <li>\n <a >Backend frameworks<\/a>\n <\/li>\n <li>\n <a >RESTful API design<\/a>\n <\/li>\n <li>\n <a >Databases and ORMs<\/a>\n <\/li>\n <\/ul>\n <\/div>\n\n <div class=\"icon-list\">\n <div class=\"top\">\n <div class=\"icon-container\">\n <svg class=\"icon icon-briefcase\" role=\"img\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" viewBox=\"0 0 25 26\" fill=\"none\"><title>briefcase<\/title><path fill=\"currentColor\" d=\"M5.469 16.125a5.446 5.446 0 0 1-3.907-1.648v6.335a2.35 2.35 0 0 0 2.344 2.344h17.188a2.35 2.35 0 0 0 2.343-2.343v-6.336a5.446 5.446 0 0 1-3.906 1.648H5.47Z\"\/><path fill=\"currentColor\" d=\"M21.094 5.969h-3.125v-.782a2.344 2.344 0 0 0-2.344-2.343h-6.25a2.344 2.344 0 0 0-2.344 2.344v.78H3.906a2.35 2.35 0 0 0-2.344 2.345v2.343a3.906 3.906 0 0 0 3.907 3.906h2.343V12.22a.781.781 0 1 1 1.563 0v2.344h6.25v-2.344a.781.781 0 1 1 1.563 0v2.344h2.343a3.907 3.907 0 0 0 3.907-3.907V8.312a2.351 2.351 0 0 0-2.344-2.343Zm-12.5-.782a.781.781 0 0 1 .781-.78h6.25a.781.781 0 0 1 .781.78v.782H8.594v-.782Z\"\/><\/svg>\n\n <\/div>\n \n <h3 class=\"title\">Backend job roles<\/h3>\n <\/div>\n\n <ul class=\"links\">\n <li>\n <a >Backend developer<\/a>\n <\/li>\n <li>\n <a >Software engineer<\/a>\n <\/li>\n <li>\n <a >Full-stack developer<\/a>\n <\/li>\n <\/ul>\n <\/div>\n\n <\/div>\n \n <\/div>\n<\/section>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"junior-backend-interview-questions\">Junior backend interview questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> What’s the difference between a framework and a library? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> A library is a collection of functions\/methods\/classes that you can call from your own code. You’re in charge of the flow of the application; you decide when to call the library. In contrast, with a framework, the flow is determined by the framework itself, invoking your code at specific points (Inversion of Control). Examples include Flask as a framework and NumPy as a library in Python.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Consider the following Python code snippet. Can you identify what’s wrong with it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def add_numbers(a, b):\n <span class=\"hljs-keyword\">return<\/span> a + b\n\n result = add_numbers(<span class=\"hljs-string\">\"5\"<\/span>, <span class=\"hljs-number\">3<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function <code>add_numbers<\/code> is trying to add a string (“5”) and an integer (3) together, which will raise a TypeError in Python. To fix it, one must ensure that both variables are of the same datatype, by converting the string to an integer.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain what a <code>JOIN<\/code> operation is in SQL. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> A <code>JOIN<\/code> operation in SQL is used to combine rows from two or more tables based on a related column between them. The most common types of JOINs include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Look at this SQL query and explain if there is any vulnerability:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> query = <span class=\"hljs-string\">\"SELECT * FROM users WHERE username = '\"<\/span> + username + <span class=\"hljs-string\">\"' AND password = '\"<\/span> + password + <span class=\"hljs-string\">\"';\"<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This query is vulnerable to SQL injection. An attacker can provide malicious input in <code>username<\/code> or <code>password<\/code> to modify the query and potentially access or harm the database. To prevent this, one should use parameterized queries or prepared statements.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Describe the concept of statelessness in RESTful APIs. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Statelessness means that each HTTP request from a client to a server must contain all the information needed to understand and process the request. The server should not store any context between requests, ensuring that each request can be understood in isolation.<\/p>\n\n\n\n<p><strong>Question:<\/strong> What’s the output of the following Python function?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> def mystery_function(a, b=[]):\n b.append(a)\n <span class=\"hljs-keyword\">return<\/span> b\n\n <span class=\"hljs-keyword\">print<\/span>(mystery_function(<span class=\"hljs-number\">1<\/span>))\n <span class=\"hljs-keyword\">print<\/span>(mystery_function(<span class=\"hljs-number\">2<\/span>))<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The output will be:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"JSON \/ JSON with Comments\" data-shcb-language-slug=\"json\"><span><code class=\"hljs language-json shcb-wrap-lines\"> [<span class=\"hljs-number\">1<\/span>]\n [<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">2<\/span>]<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JSON \/ JSON with Comments<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">json<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The mutable default argument (<code>b=[]<\/code>) is a common Python gotcha. The list <code>b<\/code> is created only once when the function is defined, so successive calls to the function reuse the same list.<\/p>\n\n\n\n<p><strong>Question:<\/strong> What is the most Pythonic way to check if a list is empty (considering you are sure the variable to test is a list) ?<\/p>\n\n\n\n<p><strong>Answer:<\/strong> <\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"><span class=\"hljs-keyword\">if<\/span> my_list:\n <span class=\"hljs-comment\"># do something when list is not empty<\/span>\n<span class=\"hljs-keyword\">else<\/span>:\n <span class=\"hljs-comment\"># do something when list is empty<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>It is not necessary to compare it with <code>== []<\/code> or to call <code>len(my_list)<\/code>. When used in a condition, the empty tuples, lists, dictionaries and sets are treated as <code>False<\/code>.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Given this simple express.js middleware, what is its purpose?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-6\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> app.use(<span class=\"hljs-function\">(<span class=\"hljs-params\">req, res, next<\/span>) =><\/span> {\n res.setHeader(<span class=\"hljs-string\">'Cache-Control'<\/span>, <span class=\"hljs-string\">'no-cache'<\/span>);\n next();\n });<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-6\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This middleware sets the <code>Cache-Control<\/code> header to <code>no-cache<\/code> for all responses. It instructs the browser (or caching servers) not to cache the content of the response, ensuring that the client always fetches the latest content from the server.<\/p>\n\n\n\n<p><strong>Question:<\/strong> How can you ensure data integrity in a relational database? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Data integrity can be maintained through the use of constraints such as primary keys, foreign keys, unique constraints, and check constraints. Regular backups, validations, and normalization can also help maintain data integrity.<\/p>\n\n\n\n<p><strong>Question:<\/strong> In the following Node.js code, what issue might arise and how can you fix it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-7\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> <span class=\"hljs-keyword\">const<\/span> fs = <span class=\"hljs-built_in\">require<\/span>(<span class=\"hljs-string\">'fs'<\/span>);\n\n fs.readFile(<span class=\"hljs-string\">'file.txt'<\/span>, <span class=\"hljs-string\">'utf8'<\/span>, (err, data) => {\n <span class=\"hljs-keyword\">if<\/span> (err) <span class=\"hljs-keyword\">throw<\/span> err;\n <span class=\"hljs-built_in\">console<\/span>.log(data);\n });\n\n fs.unlinkSync(<span class=\"hljs-string\">'file.txt'<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-7\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The code is trying to read the content of ‘file.txt’ asynchronously while it’s being deleted synchronously. There’s a race condition; the file might be deleted before the readFile operation completes, leading to an error. To fix it, the deletion should be moved inside the callback of <code>readFile<\/code> to ensure the read operation completes before the file is deleted.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"intermediate-backend-developer-questions\">Intermediate backend developer questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> Describe the differences between horizontal and vertical scaling. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Horizontal scaling<\/strong> means adding more machines to a system. This is often referred to as scaling out. For example, adding more nodes to a distributed database or adding more servers in a load-balanced environment.<\/li>\n\n\n\n<li><strong>Vertical scaling<\/strong> means increasing the resources of an existing machine, such as adding more RAM, CPU, or storage. This is often referred to as scaling up.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Analyze the potential issues with this piece of code handling database connections:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-8\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def get_data(query):\n connection = create_db_connection()\n data = connection.execute(query)\n connection.close()\n <span class=\"hljs-keyword\">return<\/span> data<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-8\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> There are a couple potential issues:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>There’s no error handling. If the connection fails or the query has issues, the code could break.<\/li>\n\n\n\n<li>Each time data is fetched, a new database connection is established and closed. This is resource-intensive and can slow down applications, especially if <code>get_data<\/code> is called frequently.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> What are microservices, and what are their benefits over a monolithic architecture? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Microservices is an architectural style that structures an application as a collection of loosely coupled, independently deployable services. Each service corresponds to a business capability and often has its own database. Benefits include better scalability, flexibility in technology choices for each service, easier maintenance and upgrades, and enhanced fault isolation.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Examine the following endpoint in a Flask application and suggest improvements:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-9\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> @app.route(<span class=\"hljs-string\">'\/users\/<id>'<\/span>, methods=[<span class=\"hljs-string\">'GET'<\/span>])\n def get_user(id):\n user = db.session.query(User).filter_by(id=id).first()\n <span class=\"hljs-keyword\">return<\/span> jsonify(user)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-9\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The function doesn’t handle the case where the user might not be found, potentially leading to a <code>None<\/code> object being passed to <code>jsonify<\/code>. To fix this, Replace the function <code>first<\/code> by the function <code>one<\/code>. Exceptions will be raised and handled by the rest of the code if there is not exactly one record found.<\/li>\n\n\n\n<li>Directly serializing the ORM object may expose sensitive fields. It’s better to use a serialization method or library to ensure only required fields are exposed.<\/li>\n\n\n\n<li>No input validation or type checking for <code>id<\/code>.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> What is the potential bottleneck in the following database query?<\/p>\n\n\n<pre class=\"wp-block-code\"><span><code class=\"hljs shcb-wrap-lines\"> SELECT * FROM orders ORDER BY creation_date DESC LIMIT 10;<\/code><\/span><\/pre>\n\n\n<p><strong>Answer:<\/strong> If there is no index on the <code>creation_date<\/code> column, sorting the table can be resource-intensive, especially as the <code>orders<\/code> table grows in size. To improve this, an index on the <code>creation_date<\/code> column should be considered.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain the concept of eventual consistency. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Eventual consistency refers to a system state where all replicas of data might not be immediately consistent but will become consistent over time. It is a relaxation of the strong consistency model to achieve higher availability and scalability in distributed systems.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Consider the following asynchronous Node.js function. What’s wrong with it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-10\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> <span class=\"hljs-keyword\">async<\/span> <span class=\"hljs-function\"><span class=\"hljs-keyword\">function<\/span> <span class=\"hljs-title\">fetchData<\/span>(<span class=\"hljs-params\"><\/span>) <\/span>{\n <span class=\"hljs-keyword\">let<\/span> data = <span class=\"hljs-keyword\">await<\/span> someAsyncFunction();\n <span class=\"hljs-keyword\">if<\/span> (!data) {\n <span class=\"hljs-keyword\">throw<\/span> <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-built_in\">Error<\/span>(<span class=\"hljs-string\">\"Data not found\"<\/span>);\n }\n <span class=\"hljs-keyword\">return<\/span> processData(data);\n }<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-10\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function lacks error handling for potential failures of <code>someAsyncFunction()<\/code>. A try-catch block should be added around the <code>await<\/code> statement to handle any errors that might arise from that asynchronous call.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Look at this Redis caching function and identify any issues:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-11\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def cache_data(key, value):\n redis_client = redis.StrictRedis(host=<span class=\"hljs-string\">'localhost'<\/span>, port=<span class=\"hljs-number\">6379<\/span>, db=<span class=\"hljs-number\">0<\/span>)\n redis_client.set(key, value)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-11\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function initializes a new Redis connection each time it’s called. This can be inefficient, especially if caching operations are frequent. It’s better to maintain a persistent Redis connection or use a connection pool.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Analyze this Django ORM query for optimization:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-12\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> books = Book.objects.all()\n <span class=\"hljs-keyword\">for<\/span> book in books:\n <span class=\"hljs-keyword\">print<\/span>(book.author.name)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-12\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This code suffers from the “N+1 queries problem”. For each book, a separate query is made to fetch the author’s name, leading to N+1 queries in total (1 to fetch all books + N to fetch the authors). The optimized version would use <code>select_related<\/code>:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-13\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> books = Book.objects.select_related(<span class=\"hljs-string\">'author'<\/span>).all()\n <span class=\"hljs-keyword\">for<\/span> book in books:\n <span class=\"hljs-keyword\">print<\/span>(book.author.name)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-13\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Question:<\/strong> How does a message queue like RabbitMQ or Kafka improve system architecture?<\/p>\n\n\n\n<p><strong>Answer:<\/strong> Message queues decouple components in a system, allowing for asynchronous processing. This means that a component can send a message to the queue without waiting for it to be processed. This has several benefits:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Improved performance and responsiveness, as components don’t block waiting for tasks to complete.<\/li>\n\n\n\n<li>Enhanced system reliability, as the message queue can act as a buffer during high traffic or if a component fails and needs to restart.<\/li>\n\n\n\n<li>Better scalability, as workers can be easily added or removed based on the workload.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"senior-backend-developer-questions\">Senior backend developer questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> Explain the principles and benefits of the Twelve-Factor App methodology. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> The Twelve-Factor App is a set of best practices for building modern, scalable, maintainable software-as-a-service apps. Some key principles include:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Codebase<\/strong>: One codebase tracked in revision control, with many deploys.<\/li>\n\n\n\n<li><strong>Dependencies<\/strong>: Explicitly declare and isolate dependencies.<\/li>\n\n\n\n<li><strong>Config<\/strong>: Store configuration in the environment.<\/li>\n\n\n\n<li><strong>Backing Services<\/strong>: Treat backing services as attached resources.<\/li>\n\n\n\n<li><strong>Build, Release, Run<\/strong>: Strictly separate build and run stages.<\/li>\n\n\n\n<li><strong>Processes<\/strong>: Execute the app as one or more stateless processes.<\/li>\n\n\n\n<li><strong>Port Binding<\/strong>: Export services via port binding.<\/li>\n\n\n\n<li><strong>Concurrency<\/strong>: Scale out via the process model.<\/li>\n\n\n\n<li><strong>Disposability<\/strong>: Maximize robustness with fast startup and graceful shutdown.<\/li>\n\n\n\n<li><strong>Dev\/Prod Parity<\/strong>: Keep development, staging, and production as similar as possible.<\/li>\n\n\n\n<li><strong>Logs<\/strong>: Treat logs as event streams.<\/li>\n\n\n\n<li><strong>Admin Processes<\/strong>: Run admin\/management tasks as one-off processes.<\/li>\n<\/ol>\n\n\n\n<p>Benefits include portability across execution environments, minimized divergence between development and production, and scalability.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain the CAP theorem and its implications in distributed systems design. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><a href=\"https:\/\/en.wikipedia.org\/wiki\/CAP_theorem\" target=\"_blank\" rel=\"noopener\"> The CAP theorem<\/a> states that it’s impossible for a distributed system to simultaneously provide all three of the following guarantees:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Consistency<\/strong>: Every read receives the most recent write.<\/li>\n\n\n\n<li><strong>Availability<\/strong>: Every request receives a (non-error) response, without a guarantee that it contains the most recent version.<\/li>\n\n\n\n<li><strong>Partition tolerance<\/strong>: The system continues to operate despite arbitrary message loss or failure of part of the system.<\/li>\n<\/ul>\n\n\n\n<p>In the face of a network partition, a system must choose between consistency and availability. This theorem guides the design and trade-offs of distributed databases and systems.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Examine the following piece of Python code and identify potential issues related to concurrency:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-14\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> counter = <span class=\"hljs-number\">0<\/span>\n\n def increment_counter():\n <span class=\"hljs-keyword\">global<\/span> counter\n <span class=\"hljs-keyword\">for<\/span> _ in range(<span class=\"hljs-number\">1000000<\/span>):\n counter += <span class=\"hljs-number\">1<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-14\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> If <code>increment_counter<\/code> is called concurrently from multiple threads or processes, there could be race conditions leading to the <code>counter<\/code> not being accurately incremented. A synchronization mechanism like locks or semaphores should be employed to protect the critical section.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Given the following SQL query, how can it be optimized for a large dataset?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-15\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> SELECT orders.id, products.name \n FROM orders \n INNER JOIN products ON orders.product_id = products.id \n WHERE products.category = <span class=\"hljs-string\">'electronics'<\/span>;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-15\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Ensure there are indices on the columns involved in the JOIN operation (<code>orders.product_id<\/code> and <code>products.id<\/code>).<\/li>\n\n\n\n<li>Add an index on <code>products.category<\/code> since it’s used in the WHERE clause.<\/li>\n\n\n\n<li>Consider denormalization or materialized views if this is a frequently executed query.<\/li>\n\n\n\n<li>Think about reworking the database schema. The field <code>products.category<\/code> could be changed to a numeric field and the correspondance between num_category and str_category could be stored in an intermediate table.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Analyze this cache invalidation strategy and suggest improvements:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-16\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def update_product(product):\n db.save(product)\n cache.delete(f<span class=\"hljs-string\">'product-{product.id}'<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-16\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> While the function updates a product in the database and invalidates the cache, a race condition could occur where the cache is repopulated with old data before the database update completes. A better strategy might be to use cache versioning or to update the cache with the new data directly after the database update, ensuring fresh data is always available.<\/p>\n\n\n\n<p><strong>Question:<\/strong> How do you handle versioning in RESTful APIs? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> There are multiple strategies:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>URI Versioning<\/strong>: Include the version in the URI, e.g., <code>\/v1\/users<\/code>.<\/li>\n\n\n\n<li><strong>Header Versioning<\/strong>: Use custom headers, e.g., <code>Accept-version: v1<\/code>.<\/li>\n\n\n\n<li><strong>Accept Header<\/strong>: Use the <code>Accept<\/code> header with a versioned media type, e.g., <code>Accept: application\/json; Version=2<\/code>.<\/li>\n\n\n\n<li><strong>Query Parameter<\/strong>: Include the version in a query parameter, e.g., <code>\/users?version=1<\/code>.<\/li>\n<\/ul>\n\n\n\n<p>It’s essential to choose a method that aligns with the organization’s goals, and it’s also vital to provide proper documentation for clients.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Here’s a simplified code to manage tasks in a queue. Identify potential pitfalls:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-17\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> tasks = []\n\n def add_task(task):\n tasks.append(task)\n\n def process_next_task():\n <span class=\"hljs-keyword\">if<\/span> tasks:\n task = tasks.pop(<span class=\"hljs-number\">0<\/span>)\n <span class=\"hljs-comment\"># process task<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-17\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The list data structure in Python is not efficient for pop operations from the start of the list. This operation is O(n). Using a data structure like <code>deque<\/code> from the <code>collections<\/code> module would be more efficient.<\/li>\n\n\n\n<li>If used in a multithreaded environment, race conditions can occur, leading to tasks being processed multiple times or not at all. Proper synchronization or thread-safe collections should be used.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Consider the following Kafka consumer code snippet. What could be problematic about this?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-18\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> consumer = KafkaConsumer(<span class=\"hljs-string\">'my_topic'<\/span>)\n <span class=\"hljs-keyword\">for<\/span> message <span class=\"hljs-keyword\">in<\/span> consumer:\n process_message(message)\n consumer.commit()<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-18\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The consumer commits after processing each message, which can be inefficient and slow down the message processing rate. Depending on the <code>process_message<\/code> function, failures might result in message loss if a message is committed but not successfully processed. It might be better to batch the commits or use a commit strategy based on time or message count.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Describe the advantages and challenges of transitioning a monolithic application to a microservices architecture. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><br><em>Advantages<\/em>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><em>Scalability<\/em>: Each service can be scaled independently based on its requirements.<\/li>\n\n\n\n<li><em>Flexibility<\/em>: Different services can use different technologies.<\/li>\n\n\n\n<li><em>Maintainability<\/em>: Smaller codebases are easier to understand and maintain.<\/li>\n\n\n\n<li><em>Faster Time to Market<\/em>: Teams can work on different services simultaneously, leading to faster feature releases. <\/li>\n<\/ul>\n\n\n\n<p><em>Challenges<\/em>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><em>Network Complexity<\/em>: Increased inter-service communication can introduce latency and complexity.<\/li>\n\n\n\n<li><em>Data Consistency<\/em>: With services having their own databases, ensuring data consistency can be challenging.<\/li>\n\n\n\n<li><em>Operational Overhead<\/em>: More services mean more things to deploy, monitor, and manage.<\/li>\n\n\n\n<li><em>Service Discovery<\/em>: Services need to discover and communicate with each other.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"more-backend-interview-resources\">More backend interview resources<\/h2>\n\n\n\n<p>For more guides on improving your knowledge of software engineer hiring, we have outlined helpful blog posts below:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/coderpad.io\/blog\/hiring-developers\/hire-back-end-developers\/\">Hire Back-End Developers: 11 strategies and niche job boards<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/blog\/hiring-developers\/software-developers-want-to-leave-their-jobs-is-your-company-ready-to-recruit\/\">Software Developers Want to Leave Their Jobs. Is Your Company Ready to Recruit?<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/blog\/interviewing\/prompt-engineering-for-technical-interview-questions\/\">Prompt Engineering for Technical Interview Questions <\/a><\/li>\n<\/ul>\n\n\n\n<p>Additionally, we offer the following backend framework interview questions:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/nodejs-interview-questions\/\">Node.js<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/ruby-on-rails-interview-questions\/\">Ruby on Rails<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/django-interview-questions\/\">Django<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/spring-interview-questions\/\">Spring<\/a><\/li>\n<\/ul>\n\n\n\n<p><\/p>\n\n\n<section class=\"logo-row-block\">\n <div class=\"inner\">\n <h2 class=\"headline\">1,000 Companies use CoderPad to Screen and Interview Developers<\/h2>\n \n <div class=\"logos logos--grayscale\" >\n <div> <svg class=\"logo logo-spotify\" role=\"img\" viewBox=\"0 0 538 167\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><title>Spotify<\/title><path d=\"M83.743 0C37.494 0 0 37.493 0 83.742c0 46.251 37.494 83.741 83.743 83.741 46.254 0 83.744-37.49 83.744-83.741 0-46.246-37.49-83.738-83.745-83.738L83.743 0zm38.404 120.78a5.217 5.217 0 0 1-7.18 1.73c-19.662-12.01-44.414-14.73-73.564-8.07a5.222 5.222 0 0 1-6.249-3.93 5.213 5.213 0 0 1 3.926-6.25c31.9-7.288 59.263-4.15 81.337 9.34 2.46 1.51 3.24 4.72 1.73 7.18zm10.25-22.802c-1.89 3.072-5.91 4.042-8.98 2.152-22.51-13.836-56.823-17.843-83.448-9.761-3.453 1.043-7.1-.903-8.148-4.35a6.538 6.538 0 0 1 4.354-8.143c30.413-9.228 68.222-4.758 94.072 11.127 3.07 1.89 4.04 5.91 2.15 8.976v-.001zm.88-23.744c-26.99-16.031-71.52-17.505-97.289-9.684-4.138 1.255-8.514-1.081-9.768-5.219a7.835 7.835 0 0 1 5.221-9.771c29.581-8.98 78.756-7.245 109.83 11.202a7.823 7.823 0 0 1 2.74 10.733c-2.2 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xmlns=\"http:\/\/www.w3.org\/2000\/svg\" fill=\"none\" viewBox=\"0 0 206 31\"><title>Chart boost<\/title><g fill=\"currentColor\" clip-path=\"url(#chartboost-a)\"><path d=\"M44.577 18.523c0-7.131 4.357-11.975 11.108-11.975 5.153 0 8.912 3.027 9.777 7.905h-3.06c-.898-3.263-3.36-5.215-6.851-5.215-4.89 0-8.016 3.836-8.016 9.285 0 5.448 2.993 9.284 7.882 9.284 3.593 0 6.087-1.918 6.95-5.215h3.061c-.865 4.878-4.724 7.905-9.977 7.905-6.683.003-10.874-4.775-10.874-11.974m38.345 2.22v9.553h-2.728v-9.383c0-3.566-1.697-5.449-4.624-5.449-3.16 0-5.123 2.08-5.123 6.258v8.58H67.72V6.547h2.727v9.918c.795-2.171 2.728-3.528 5.587-3.528 3.793 0 6.885 2.12 6.885 7.805zm18.795 7.033v2.522h-1.498c-2.26 0-1.973-1.56-2.007-3.242-.837 2.14-3.812 3.444-6.74 3.444-3.724 0-6.252-1.884-6.252-5.011 0-3.43 2.36-5.348 6.82-5.348h4.988v-1.178c0-2.22-1.564-3.565-4.223-3.565-2.395 0-3.992 1.143-4.325 2.894h-2.728c.399-3.364 3.092-5.348 7.184-5.348 4.322 0 6.82 2.186 6.82 6.189v7.502c0 .907.332 1.143 1.096 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id=\"chartboost-a\"><path fill=\"currentColor\" d=\"M.158.5h205v30h-205z\"\/><\/clipPath><\/defs><\/svg>\n\n<\/div>\n <\/div>\n <\/div>\n<\/section>\n\n\n\n<div class=\"wp-block-columns\">\n<div class=\"wp-block-column\"><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img decoding=\"async\" src=\"https:\/\/d2h1bfu6zrdxog.cloudfront.net\/wp-content\/uploads\/2023\/03\/g2-leader-winter-2023.png\" alt=\"\" class=\"wp-image-32119\"\/><\/figure>\n<\/div><\/div>\n\n\n\n<div class=\"wp-block-column\"><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img decoding=\"async\" src=\"https:\/\/d2h1bfu6zrdxog.cloudfront.net\/wp-content\/uploads\/2023\/03\/g2-users-love-us.png\" alt=\"\" class=\"wp-image-32120\"\/><\/figure>\n<\/div><\/div>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"best-interview-practices-for-backend-roles\">Best interview practices for backend roles<\/h2>\n\n\n\n<p>The backend interview process can often be quite diverse, influenced by various elements including the specific engineering role in focus and the applicant’s level of expertise in backend technologies. To enhance the effectiveness of your backend interview questions, consider adopting the following strategies when interacting with potential recruits:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Develop technical queries that reflect actual scenarios encountered in your organization – this approach is not only more engaging for the candidate but also serves as a more accurate gauge of how their skill set aligns with your team’s needs.<\/li>\n\n\n\n<li>Encourage a participatory environment by allowing the candidate to pose questions throughout the process.<\/li>\n\n\n\n<li>Given that backend candidates may sometimes need to collaborate with front-end teams, it is advantageous for them to have a foundational understanding of the principles that govern user interface and user experience design.<\/li>\n<\/ul>\n\n\n\n<p>Furthermore, adhering to standard interview protocols remains crucial during backend interview sessions – adjust the complexity of interview questions based on the candidate’s evolving expertise, provide timely feedback regarding their status in the recruitment process, and offer sufficient opportunities for candidates to discuss the evaluation or delve into the nuances of collaborating with your team.<\/p>\n","protected":false},"parent":0,"menu_order":0,"template":"","class_list":["post-36441","interview-questions","type-interview-questions","status-publish","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/interview-questions\/36441","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/interview-questions"}],"about":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/types\/interview-questions"}],"wp:attachment":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/media?parent=36441"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
query Query {allPlanets{planets{name population terrains climates}}}<\/code><\/p>\n\n\n\n(View the shape of the data here<\/a>.)<\/p>\n\n\n\n2. Store the data from the graphql endpoint into the database and create appropriate models<\/p>\n\n\n\n3. Write RESTful Create, Read, Update, and Delete endpoints to interact with the database<\/p>\n\n\n\n\t<\/iframe>\n<\/div>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"question-2-shopping-list\"><strong>Question 2: Shopping List<\/strong><\/h3>\n\n\n\n<p>This question tests a candidate’s ability to create model(s) for the data structure, insert hard-coded data into a database, modify tables and fields in a database, and write endpoints to interact with data.<\/p>\n\n\n\n<p><strong>Part 1<\/strong><\/p>\n\n\n\n<p><em>Create a model for the shopping lists and items located in app\/data\/data.ts.<\/em><\/p>\n\n\n\n<p><strong>Part 2<\/strong><\/p>\n\n\n\n<p><em>Store the shopping lists and items located in app\/data\/data.ts in the database.<\/em><\/p>\n\n\n\n<p><strong>Part 3<\/strong><\/p>\n\n\n\n<p><em>Modify the database such that a price field can be stored for each item.<\/em><\/p>\n\n\n\n<p><strong>Part 4<\/strong><\/p>\n\n\n\n<p><em>Multiply the quantity of each item in the shopping lists by two.<\/em><\/p>\n\n\n\n<p><strong>Part 5<\/strong><\/p>\n\n\n\n<p><em>Create API endpoints to dynamically get a list of shopping lists and items.<\/em><\/p>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"assessing-the-candidate\"><strong>Assessing the candidate<\/strong><\/h4>\n\n\n\n<p>The candidate should create models for a shopping list and items. They should then write code to create the tables necessary and insert the data into the tables. Additionally, the candidate can be asked to edit the data in the tables and add additional fields. Finally, endpoints to interact with the data can be created.<\/p>\n\n\n<div\n\tclass=\"sandbox-embed responsive-embed sandbox-embed--full-width\"\n\tstyle=\"padding-top: 85%\"\ndata-block-name=\"coderpad-sandbox-embed\">\n\t<iframe src=\"https:\/\/embed.coderpad.io\/sandbox?question_id=254803u0026use_question_button\" width=\"640\" height=\"544\" loading=\"lazy\" aria-label=\"Try out the CoderPad sandbox\"><\/iframe>\n<\/div>\n\n\n<section class=\"\n\ticon-lists-block\n\t\n\" data-block-name=\"coderpad-icon-lists-block\">\n <div class=\"inner\">\n\n \n <div class=\"lists lists--2\">\n <div class=\"icon-list\">\n <div class=\"top\">\n <div class=\"icon-container\">\n <svg class=\"icon icon-lightning-bolt\" role=\"img\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" fill=\"none\" viewBox=\"0 0 10 14\"><title>lightning bolt<\/title><path fill=\"currentColor\" d=\"M3.608 13.967c.185.079.4.013.508-.158l4.922-7.82a.41.41 0 0 0-.347-.63H5.407L6.628.511a.41.41 0 0 0-.744-.32L.962 8.011a.41.41 0 0 0 .347.63h3.284l-1.221 4.848a.41.41 0 0 0 .236.478Z\"\/><\/svg>\n\n <\/div>\n \n <h3 class=\"title\">Backend skills to assess<\/h3>\n <\/div>\n\n <ul class=\"links\">\n <li>\n <a >Backend frameworks<\/a>\n <\/li>\n <li>\n <a >RESTful API design<\/a>\n <\/li>\n <li>\n <a >Databases and ORMs<\/a>\n <\/li>\n <\/ul>\n <\/div>\n\n <div class=\"icon-list\">\n <div class=\"top\">\n <div class=\"icon-container\">\n <svg class=\"icon icon-briefcase\" role=\"img\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" viewBox=\"0 0 25 26\" fill=\"none\"><title>briefcase<\/title><path fill=\"currentColor\" d=\"M5.469 16.125a5.446 5.446 0 0 1-3.907-1.648v6.335a2.35 2.35 0 0 0 2.344 2.344h17.188a2.35 2.35 0 0 0 2.343-2.343v-6.336a5.446 5.446 0 0 1-3.906 1.648H5.47Z\"\/><path fill=\"currentColor\" d=\"M21.094 5.969h-3.125v-.782a2.344 2.344 0 0 0-2.344-2.343h-6.25a2.344 2.344 0 0 0-2.344 2.344v.78H3.906a2.35 2.35 0 0 0-2.344 2.345v2.343a3.906 3.906 0 0 0 3.907 3.906h2.343V12.22a.781.781 0 1 1 1.563 0v2.344h6.25v-2.344a.781.781 0 1 1 1.563 0v2.344h2.343a3.907 3.907 0 0 0 3.907-3.907V8.312a2.351 2.351 0 0 0-2.344-2.343Zm-12.5-.782a.781.781 0 0 1 .781-.78h6.25a.781.781 0 0 1 .781.78v.782H8.594v-.782Z\"\/><\/svg>\n\n <\/div>\n \n <h3 class=\"title\">Backend job roles<\/h3>\n <\/div>\n\n <ul class=\"links\">\n <li>\n <a >Backend developer<\/a>\n <\/li>\n <li>\n <a >Software engineer<\/a>\n <\/li>\n <li>\n <a >Full-stack developer<\/a>\n <\/li>\n <\/ul>\n <\/div>\n\n <\/div>\n \n <\/div>\n<\/section>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"junior-backend-interview-questions\">Junior backend interview questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> What’s the difference between a framework and a library? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> A library is a collection of functions\/methods\/classes that you can call from your own code. You’re in charge of the flow of the application; you decide when to call the library. In contrast, with a framework, the flow is determined by the framework itself, invoking your code at specific points (Inversion of Control). Examples include Flask as a framework and NumPy as a library in Python.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Consider the following Python code snippet. Can you identify what’s wrong with it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def add_numbers(a, b):\n <span class=\"hljs-keyword\">return<\/span> a + b\n\n result = add_numbers(<span class=\"hljs-string\">\"5\"<\/span>, <span class=\"hljs-number\">3<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function <code>add_numbers<\/code> is trying to add a string (“5”) and an integer (3) together, which will raise a TypeError in Python. To fix it, one must ensure that both variables are of the same datatype, by converting the string to an integer.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain what a <code>JOIN<\/code> operation is in SQL. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> A <code>JOIN<\/code> operation in SQL is used to combine rows from two or more tables based on a related column between them. The most common types of JOINs include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Look at this SQL query and explain if there is any vulnerability:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> query = <span class=\"hljs-string\">\"SELECT * FROM users WHERE username = '\"<\/span> + username + <span class=\"hljs-string\">\"' AND password = '\"<\/span> + password + <span class=\"hljs-string\">\"';\"<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This query is vulnerable to SQL injection. An attacker can provide malicious input in <code>username<\/code> or <code>password<\/code> to modify the query and potentially access or harm the database. To prevent this, one should use parameterized queries or prepared statements.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Describe the concept of statelessness in RESTful APIs. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Statelessness means that each HTTP request from a client to a server must contain all the information needed to understand and process the request. The server should not store any context between requests, ensuring that each request can be understood in isolation.<\/p>\n\n\n\n<p><strong>Question:<\/strong> What’s the output of the following Python function?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> def mystery_function(a, b=[]):\n b.append(a)\n <span class=\"hljs-keyword\">return<\/span> b\n\n <span class=\"hljs-keyword\">print<\/span>(mystery_function(<span class=\"hljs-number\">1<\/span>))\n <span class=\"hljs-keyword\">print<\/span>(mystery_function(<span class=\"hljs-number\">2<\/span>))<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The output will be:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"JSON \/ JSON with Comments\" data-shcb-language-slug=\"json\"><span><code class=\"hljs language-json shcb-wrap-lines\"> [<span class=\"hljs-number\">1<\/span>]\n [<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">2<\/span>]<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JSON \/ JSON with Comments<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">json<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The mutable default argument (<code>b=[]<\/code>) is a common Python gotcha. The list <code>b<\/code> is created only once when the function is defined, so successive calls to the function reuse the same list.<\/p>\n\n\n\n<p><strong>Question:<\/strong> What is the most Pythonic way to check if a list is empty (considering you are sure the variable to test is a list) ?<\/p>\n\n\n\n<p><strong>Answer:<\/strong> <\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"><span class=\"hljs-keyword\">if<\/span> my_list:\n <span class=\"hljs-comment\"># do something when list is not empty<\/span>\n<span class=\"hljs-keyword\">else<\/span>:\n <span class=\"hljs-comment\"># do something when list is empty<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>It is not necessary to compare it with <code>== []<\/code> or to call <code>len(my_list)<\/code>. When used in a condition, the empty tuples, lists, dictionaries and sets are treated as <code>False<\/code>.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Given this simple express.js middleware, what is its purpose?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-6\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> app.use(<span class=\"hljs-function\">(<span class=\"hljs-params\">req, res, next<\/span>) =><\/span> {\n res.setHeader(<span class=\"hljs-string\">'Cache-Control'<\/span>, <span class=\"hljs-string\">'no-cache'<\/span>);\n next();\n });<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-6\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This middleware sets the <code>Cache-Control<\/code> header to <code>no-cache<\/code> for all responses. It instructs the browser (or caching servers) not to cache the content of the response, ensuring that the client always fetches the latest content from the server.<\/p>\n\n\n\n<p><strong>Question:<\/strong> How can you ensure data integrity in a relational database? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Data integrity can be maintained through the use of constraints such as primary keys, foreign keys, unique constraints, and check constraints. Regular backups, validations, and normalization can also help maintain data integrity.<\/p>\n\n\n\n<p><strong>Question:<\/strong> In the following Node.js code, what issue might arise and how can you fix it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-7\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> <span class=\"hljs-keyword\">const<\/span> fs = <span class=\"hljs-built_in\">require<\/span>(<span class=\"hljs-string\">'fs'<\/span>);\n\n fs.readFile(<span class=\"hljs-string\">'file.txt'<\/span>, <span class=\"hljs-string\">'utf8'<\/span>, (err, data) => {\n <span class=\"hljs-keyword\">if<\/span> (err) <span class=\"hljs-keyword\">throw<\/span> err;\n <span class=\"hljs-built_in\">console<\/span>.log(data);\n });\n\n fs.unlinkSync(<span class=\"hljs-string\">'file.txt'<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-7\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The code is trying to read the content of ‘file.txt’ asynchronously while it’s being deleted synchronously. There’s a race condition; the file might be deleted before the readFile operation completes, leading to an error. To fix it, the deletion should be moved inside the callback of <code>readFile<\/code> to ensure the read operation completes before the file is deleted.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"intermediate-backend-developer-questions\">Intermediate backend developer questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> Describe the differences between horizontal and vertical scaling. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Horizontal scaling<\/strong> means adding more machines to a system. This is often referred to as scaling out. For example, adding more nodes to a distributed database or adding more servers in a load-balanced environment.<\/li>\n\n\n\n<li><strong>Vertical scaling<\/strong> means increasing the resources of an existing machine, such as adding more RAM, CPU, or storage. This is often referred to as scaling up.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Analyze the potential issues with this piece of code handling database connections:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-8\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def get_data(query):\n connection = create_db_connection()\n data = connection.execute(query)\n connection.close()\n <span class=\"hljs-keyword\">return<\/span> data<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-8\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> There are a couple potential issues:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>There’s no error handling. If the connection fails or the query has issues, the code could break.<\/li>\n\n\n\n<li>Each time data is fetched, a new database connection is established and closed. This is resource-intensive and can slow down applications, especially if <code>get_data<\/code> is called frequently.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> What are microservices, and what are their benefits over a monolithic architecture? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Microservices is an architectural style that structures an application as a collection of loosely coupled, independently deployable services. Each service corresponds to a business capability and often has its own database. Benefits include better scalability, flexibility in technology choices for each service, easier maintenance and upgrades, and enhanced fault isolation.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Examine the following endpoint in a Flask application and suggest improvements:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-9\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> @app.route(<span class=\"hljs-string\">'\/users\/<id>'<\/span>, methods=[<span class=\"hljs-string\">'GET'<\/span>])\n def get_user(id):\n user = db.session.query(User).filter_by(id=id).first()\n <span class=\"hljs-keyword\">return<\/span> jsonify(user)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-9\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The function doesn’t handle the case where the user might not be found, potentially leading to a <code>None<\/code> object being passed to <code>jsonify<\/code>. To fix this, Replace the function <code>first<\/code> by the function <code>one<\/code>. Exceptions will be raised and handled by the rest of the code if there is not exactly one record found.<\/li>\n\n\n\n<li>Directly serializing the ORM object may expose sensitive fields. It’s better to use a serialization method or library to ensure only required fields are exposed.<\/li>\n\n\n\n<li>No input validation or type checking for <code>id<\/code>.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> What is the potential bottleneck in the following database query?<\/p>\n\n\n<pre class=\"wp-block-code\"><span><code class=\"hljs shcb-wrap-lines\"> SELECT * FROM orders ORDER BY creation_date DESC LIMIT 10;<\/code><\/span><\/pre>\n\n\n<p><strong>Answer:<\/strong> If there is no index on the <code>creation_date<\/code> column, sorting the table can be resource-intensive, especially as the <code>orders<\/code> table grows in size. To improve this, an index on the <code>creation_date<\/code> column should be considered.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain the concept of eventual consistency. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Eventual consistency refers to a system state where all replicas of data might not be immediately consistent but will become consistent over time. It is a relaxation of the strong consistency model to achieve higher availability and scalability in distributed systems.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Consider the following asynchronous Node.js function. What’s wrong with it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-10\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> <span class=\"hljs-keyword\">async<\/span> <span class=\"hljs-function\"><span class=\"hljs-keyword\">function<\/span> <span class=\"hljs-title\">fetchData<\/span>(<span class=\"hljs-params\"><\/span>) <\/span>{\n <span class=\"hljs-keyword\">let<\/span> data = <span class=\"hljs-keyword\">await<\/span> someAsyncFunction();\n <span class=\"hljs-keyword\">if<\/span> (!data) {\n <span class=\"hljs-keyword\">throw<\/span> <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-built_in\">Error<\/span>(<span class=\"hljs-string\">\"Data not found\"<\/span>);\n }\n <span class=\"hljs-keyword\">return<\/span> processData(data);\n }<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-10\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function lacks error handling for potential failures of <code>someAsyncFunction()<\/code>. A try-catch block should be added around the <code>await<\/code> statement to handle any errors that might arise from that asynchronous call.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Look at this Redis caching function and identify any issues:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-11\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def cache_data(key, value):\n redis_client = redis.StrictRedis(host=<span class=\"hljs-string\">'localhost'<\/span>, port=<span class=\"hljs-number\">6379<\/span>, db=<span class=\"hljs-number\">0<\/span>)\n redis_client.set(key, value)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-11\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function initializes a new Redis connection each time it’s called. This can be inefficient, especially if caching operations are frequent. It’s better to maintain a persistent Redis connection or use a connection pool.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Analyze this Django ORM query for optimization:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-12\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> books = Book.objects.all()\n <span class=\"hljs-keyword\">for<\/span> book in books:\n <span class=\"hljs-keyword\">print<\/span>(book.author.name)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-12\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This code suffers from the “N+1 queries problem”. For each book, a separate query is made to fetch the author’s name, leading to N+1 queries in total (1 to fetch all books + N to fetch the authors). The optimized version would use <code>select_related<\/code>:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-13\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> books = Book.objects.select_related(<span class=\"hljs-string\">'author'<\/span>).all()\n <span class=\"hljs-keyword\">for<\/span> book in books:\n <span class=\"hljs-keyword\">print<\/span>(book.author.name)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-13\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Question:<\/strong> How does a message queue like RabbitMQ or Kafka improve system architecture?<\/p>\n\n\n\n<p><strong>Answer:<\/strong> Message queues decouple components in a system, allowing for asynchronous processing. This means that a component can send a message to the queue without waiting for it to be processed. This has several benefits:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Improved performance and responsiveness, as components don’t block waiting for tasks to complete.<\/li>\n\n\n\n<li>Enhanced system reliability, as the message queue can act as a buffer during high traffic or if a component fails and needs to restart.<\/li>\n\n\n\n<li>Better scalability, as workers can be easily added or removed based on the workload.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"senior-backend-developer-questions\">Senior backend developer questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> Explain the principles and benefits of the Twelve-Factor App methodology. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> The Twelve-Factor App is a set of best practices for building modern, scalable, maintainable software-as-a-service apps. Some key principles include:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Codebase<\/strong>: One codebase tracked in revision control, with many deploys.<\/li>\n\n\n\n<li><strong>Dependencies<\/strong>: Explicitly declare and isolate dependencies.<\/li>\n\n\n\n<li><strong>Config<\/strong>: Store configuration in the environment.<\/li>\n\n\n\n<li><strong>Backing Services<\/strong>: Treat backing services as attached resources.<\/li>\n\n\n\n<li><strong>Build, Release, Run<\/strong>: Strictly separate build and run stages.<\/li>\n\n\n\n<li><strong>Processes<\/strong>: Execute the app as one or more stateless processes.<\/li>\n\n\n\n<li><strong>Port Binding<\/strong>: Export services via port binding.<\/li>\n\n\n\n<li><strong>Concurrency<\/strong>: Scale out via the process model.<\/li>\n\n\n\n<li><strong>Disposability<\/strong>: Maximize robustness with fast startup and graceful shutdown.<\/li>\n\n\n\n<li><strong>Dev\/Prod Parity<\/strong>: Keep development, staging, and production as similar as possible.<\/li>\n\n\n\n<li><strong>Logs<\/strong>: Treat logs as event streams.<\/li>\n\n\n\n<li><strong>Admin Processes<\/strong>: Run admin\/management tasks as one-off processes.<\/li>\n<\/ol>\n\n\n\n<p>Benefits include portability across execution environments, minimized divergence between development and production, and scalability.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain the CAP theorem and its implications in distributed systems design. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><a href=\"https:\/\/en.wikipedia.org\/wiki\/CAP_theorem\" target=\"_blank\" rel=\"noopener\"> The CAP theorem<\/a> states that it’s impossible for a distributed system to simultaneously provide all three of the following guarantees:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Consistency<\/strong>: Every read receives the most recent write.<\/li>\n\n\n\n<li><strong>Availability<\/strong>: Every request receives a (non-error) response, without a guarantee that it contains the most recent version.<\/li>\n\n\n\n<li><strong>Partition tolerance<\/strong>: The system continues to operate despite arbitrary message loss or failure of part of the system.<\/li>\n<\/ul>\n\n\n\n<p>In the face of a network partition, a system must choose between consistency and availability. This theorem guides the design and trade-offs of distributed databases and systems.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Examine the following piece of Python code and identify potential issues related to concurrency:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-14\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> counter = <span class=\"hljs-number\">0<\/span>\n\n def increment_counter():\n <span class=\"hljs-keyword\">global<\/span> counter\n <span class=\"hljs-keyword\">for<\/span> _ in range(<span class=\"hljs-number\">1000000<\/span>):\n counter += <span class=\"hljs-number\">1<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-14\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> If <code>increment_counter<\/code> is called concurrently from multiple threads or processes, there could be race conditions leading to the <code>counter<\/code> not being accurately incremented. A synchronization mechanism like locks or semaphores should be employed to protect the critical section.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Given the following SQL query, how can it be optimized for a large dataset?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-15\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> SELECT orders.id, products.name \n FROM orders \n INNER JOIN products ON orders.product_id = products.id \n WHERE products.category = <span class=\"hljs-string\">'electronics'<\/span>;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-15\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Ensure there are indices on the columns involved in the JOIN operation (<code>orders.product_id<\/code> and <code>products.id<\/code>).<\/li>\n\n\n\n<li>Add an index on <code>products.category<\/code> since it’s used in the WHERE clause.<\/li>\n\n\n\n<li>Consider denormalization or materialized views if this is a frequently executed query.<\/li>\n\n\n\n<li>Think about reworking the database schema. The field <code>products.category<\/code> could be changed to a numeric field and the correspondance between num_category and str_category could be stored in an intermediate table.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Analyze this cache invalidation strategy and suggest improvements:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-16\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def update_product(product):\n db.save(product)\n cache.delete(f<span class=\"hljs-string\">'product-{product.id}'<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-16\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> While the function updates a product in the database and invalidates the cache, a race condition could occur where the cache is repopulated with old data before the database update completes. A better strategy might be to use cache versioning or to update the cache with the new data directly after the database update, ensuring fresh data is always available.<\/p>\n\n\n\n<p><strong>Question:<\/strong> How do you handle versioning in RESTful APIs? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> There are multiple strategies:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>URI Versioning<\/strong>: Include the version in the URI, e.g., <code>\/v1\/users<\/code>.<\/li>\n\n\n\n<li><strong>Header Versioning<\/strong>: Use custom headers, e.g., <code>Accept-version: v1<\/code>.<\/li>\n\n\n\n<li><strong>Accept Header<\/strong>: Use the <code>Accept<\/code> header with a versioned media type, e.g., <code>Accept: application\/json; Version=2<\/code>.<\/li>\n\n\n\n<li><strong>Query Parameter<\/strong>: Include the version in a query parameter, e.g., <code>\/users?version=1<\/code>.<\/li>\n<\/ul>\n\n\n\n<p>It’s essential to choose a method that aligns with the organization’s goals, and it’s also vital to provide proper documentation for clients.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Here’s a simplified code to manage tasks in a queue. Identify potential pitfalls:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-17\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> tasks = []\n\n def add_task(task):\n tasks.append(task)\n\n def process_next_task():\n <span class=\"hljs-keyword\">if<\/span> tasks:\n task = tasks.pop(<span class=\"hljs-number\">0<\/span>)\n <span class=\"hljs-comment\"># process task<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-17\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The list data structure in Python is not efficient for pop operations from the start of the list. This operation is O(n). Using a data structure like <code>deque<\/code> from the <code>collections<\/code> module would be more efficient.<\/li>\n\n\n\n<li>If used in a multithreaded environment, race conditions can occur, leading to tasks being processed multiple times or not at all. Proper synchronization or thread-safe collections should be used.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Consider the following Kafka consumer code snippet. What could be problematic about this?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-18\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> consumer = KafkaConsumer(<span class=\"hljs-string\">'my_topic'<\/span>)\n <span class=\"hljs-keyword\">for<\/span> message <span class=\"hljs-keyword\">in<\/span> consumer:\n process_message(message)\n consumer.commit()<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-18\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The consumer commits after processing each message, which can be inefficient and slow down the message processing rate. Depending on the <code>process_message<\/code> function, failures might result in message loss if a message is committed but not successfully processed. It might be better to batch the commits or use a commit strategy based on time or message count.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Describe the advantages and challenges of transitioning a monolithic application to a microservices architecture. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><br><em>Advantages<\/em>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><em>Scalability<\/em>: Each service can be scaled independently based on its requirements.<\/li>\n\n\n\n<li><em>Flexibility<\/em>: Different services can use different technologies.<\/li>\n\n\n\n<li><em>Maintainability<\/em>: Smaller codebases are easier to understand and maintain.<\/li>\n\n\n\n<li><em>Faster Time to Market<\/em>: Teams can work on different services simultaneously, leading to faster feature releases. <\/li>\n<\/ul>\n\n\n\n<p><em>Challenges<\/em>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><em>Network Complexity<\/em>: Increased inter-service communication can introduce latency and complexity.<\/li>\n\n\n\n<li><em>Data Consistency<\/em>: With services having their own databases, ensuring data consistency can be challenging.<\/li>\n\n\n\n<li><em>Operational Overhead<\/em>: More services mean more things to deploy, monitor, and manage.<\/li>\n\n\n\n<li><em>Service Discovery<\/em>: Services need to discover and communicate with each other.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"more-backend-interview-resources\">More backend interview resources<\/h2>\n\n\n\n<p>For more guides on improving your knowledge of software engineer hiring, we have outlined helpful blog posts below:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/coderpad.io\/blog\/hiring-developers\/hire-back-end-developers\/\">Hire Back-End Developers: 11 strategies and niche job boards<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/blog\/hiring-developers\/software-developers-want-to-leave-their-jobs-is-your-company-ready-to-recruit\/\">Software Developers Want to Leave Their Jobs. Is Your Company Ready to Recruit?<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/blog\/interviewing\/prompt-engineering-for-technical-interview-questions\/\">Prompt Engineering for Technical Interview Questions <\/a><\/li>\n<\/ul>\n\n\n\n<p>Additionally, we offer the following backend framework interview questions:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/nodejs-interview-questions\/\">Node.js<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/ruby-on-rails-interview-questions\/\">Ruby on Rails<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/django-interview-questions\/\">Django<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/spring-interview-questions\/\">Spring<\/a><\/li>\n<\/ul>\n\n\n\n<p><\/p>\n\n\n<section class=\"logo-row-block\">\n <div class=\"inner\">\n <h2 class=\"headline\">1,000 Companies use CoderPad to Screen and Interview 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id=\"chartboost-a\"><path fill=\"currentColor\" d=\"M.158.5h205v30h-205z\"\/><\/clipPath><\/defs><\/svg>\n\n<\/div>\n <\/div>\n <\/div>\n<\/section>\n\n\n\n<div class=\"wp-block-columns\">\n<div class=\"wp-block-column\"><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img decoding=\"async\" src=\"https:\/\/d2h1bfu6zrdxog.cloudfront.net\/wp-content\/uploads\/2023\/03\/g2-leader-winter-2023.png\" alt=\"\" class=\"wp-image-32119\"\/><\/figure>\n<\/div><\/div>\n\n\n\n<div class=\"wp-block-column\"><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img decoding=\"async\" src=\"https:\/\/d2h1bfu6zrdxog.cloudfront.net\/wp-content\/uploads\/2023\/03\/g2-users-love-us.png\" alt=\"\" class=\"wp-image-32120\"\/><\/figure>\n<\/div><\/div>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"best-interview-practices-for-backend-roles\">Best interview practices for backend roles<\/h2>\n\n\n\n<p>The backend interview process can often be quite diverse, influenced by various elements including the specific engineering role in focus and the applicant’s level of expertise in backend technologies. To enhance the effectiveness of your backend interview questions, consider adopting the following strategies when interacting with potential recruits:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Develop technical queries that reflect actual scenarios encountered in your organization – this approach is not only more engaging for the candidate but also serves as a more accurate gauge of how their skill set aligns with your team’s needs.<\/li>\n\n\n\n<li>Encourage a participatory environment by allowing the candidate to pose questions throughout the process.<\/li>\n\n\n\n<li>Given that backend candidates may sometimes need to collaborate with front-end teams, it is advantageous for them to have a foundational understanding of the principles that govern user interface and user experience design.<\/li>\n<\/ul>\n\n\n\n<p>Furthermore, adhering to standard interview protocols remains crucial during backend interview sessions – adjust the complexity of interview questions based on the candidate’s evolving expertise, provide timely feedback regarding their status in the recruitment process, and offer sufficient opportunities for candidates to discuss the evaluation or delve into the nuances of collaborating with your team.<\/p>\n","protected":false},"parent":0,"menu_order":0,"template":"","class_list":["post-36441","interview-questions","type-interview-questions","status-publish","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/interview-questions\/36441","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/interview-questions"}],"about":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/types\/interview-questions"}],"wp:attachment":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/media?parent=36441"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
(View the shape of the data here<\/a>.)<\/p>\n\n\n\n2. Store the data from the graphql endpoint into the database and create appropriate models<\/p>\n\n\n\n3. Write RESTful Create, Read, Update, and Delete endpoints to interact with the database<\/p>\n\n\n\n\t<\/iframe>\n<\/div>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"question-2-shopping-list\"><strong>Question 2: Shopping List<\/strong><\/h3>\n\n\n\n<p>This question tests a candidate’s ability to create model(s) for the data structure, insert hard-coded data into a database, modify tables and fields in a database, and write endpoints to interact with data.<\/p>\n\n\n\n<p><strong>Part 1<\/strong><\/p>\n\n\n\n<p><em>Create a model for the shopping lists and items located in app\/data\/data.ts.<\/em><\/p>\n\n\n\n<p><strong>Part 2<\/strong><\/p>\n\n\n\n<p><em>Store the shopping lists and items located in app\/data\/data.ts in the database.<\/em><\/p>\n\n\n\n<p><strong>Part 3<\/strong><\/p>\n\n\n\n<p><em>Modify the database such that a price field can be stored for each item.<\/em><\/p>\n\n\n\n<p><strong>Part 4<\/strong><\/p>\n\n\n\n<p><em>Multiply the quantity of each item in the shopping lists by two.<\/em><\/p>\n\n\n\n<p><strong>Part 5<\/strong><\/p>\n\n\n\n<p><em>Create API endpoints to dynamically get a list of shopping lists and items.<\/em><\/p>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"assessing-the-candidate\"><strong>Assessing the candidate<\/strong><\/h4>\n\n\n\n<p>The candidate should create models for a shopping list and items. They should then write code to create the tables necessary and insert the data into the tables. Additionally, the candidate can be asked to edit the data in the tables and add additional fields. Finally, endpoints to interact with the data can be created.<\/p>\n\n\n<div\n\tclass=\"sandbox-embed responsive-embed sandbox-embed--full-width\"\n\tstyle=\"padding-top: 85%\"\ndata-block-name=\"coderpad-sandbox-embed\">\n\t<iframe src=\"https:\/\/embed.coderpad.io\/sandbox?question_id=254803u0026use_question_button\" width=\"640\" height=\"544\" loading=\"lazy\" aria-label=\"Try out the CoderPad sandbox\"><\/iframe>\n<\/div>\n\n\n<section class=\"\n\ticon-lists-block\n\t\n\" data-block-name=\"coderpad-icon-lists-block\">\n <div class=\"inner\">\n\n \n <div class=\"lists lists--2\">\n <div class=\"icon-list\">\n <div class=\"top\">\n <div class=\"icon-container\">\n <svg class=\"icon icon-lightning-bolt\" role=\"img\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" fill=\"none\" viewBox=\"0 0 10 14\"><title>lightning bolt<\/title><path fill=\"currentColor\" d=\"M3.608 13.967c.185.079.4.013.508-.158l4.922-7.82a.41.41 0 0 0-.347-.63H5.407L6.628.511a.41.41 0 0 0-.744-.32L.962 8.011a.41.41 0 0 0 .347.63h3.284l-1.221 4.848a.41.41 0 0 0 .236.478Z\"\/><\/svg>\n\n <\/div>\n \n <h3 class=\"title\">Backend skills to assess<\/h3>\n <\/div>\n\n <ul class=\"links\">\n <li>\n <a >Backend frameworks<\/a>\n <\/li>\n <li>\n <a >RESTful API design<\/a>\n <\/li>\n <li>\n <a >Databases and ORMs<\/a>\n <\/li>\n <\/ul>\n <\/div>\n\n <div class=\"icon-list\">\n <div class=\"top\">\n <div class=\"icon-container\">\n <svg class=\"icon icon-briefcase\" role=\"img\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" viewBox=\"0 0 25 26\" fill=\"none\"><title>briefcase<\/title><path fill=\"currentColor\" d=\"M5.469 16.125a5.446 5.446 0 0 1-3.907-1.648v6.335a2.35 2.35 0 0 0 2.344 2.344h17.188a2.35 2.35 0 0 0 2.343-2.343v-6.336a5.446 5.446 0 0 1-3.906 1.648H5.47Z\"\/><path fill=\"currentColor\" d=\"M21.094 5.969h-3.125v-.782a2.344 2.344 0 0 0-2.344-2.343h-6.25a2.344 2.344 0 0 0-2.344 2.344v.78H3.906a2.35 2.35 0 0 0-2.344 2.345v2.343a3.906 3.906 0 0 0 3.907 3.906h2.343V12.22a.781.781 0 1 1 1.563 0v2.344h6.25v-2.344a.781.781 0 1 1 1.563 0v2.344h2.343a3.907 3.907 0 0 0 3.907-3.907V8.312a2.351 2.351 0 0 0-2.344-2.343Zm-12.5-.782a.781.781 0 0 1 .781-.78h6.25a.781.781 0 0 1 .781.78v.782H8.594v-.782Z\"\/><\/svg>\n\n <\/div>\n \n <h3 class=\"title\">Backend job roles<\/h3>\n <\/div>\n\n <ul class=\"links\">\n <li>\n <a >Backend developer<\/a>\n <\/li>\n <li>\n <a >Software engineer<\/a>\n <\/li>\n <li>\n <a >Full-stack developer<\/a>\n <\/li>\n <\/ul>\n <\/div>\n\n <\/div>\n \n <\/div>\n<\/section>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"junior-backend-interview-questions\">Junior backend interview questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> What’s the difference between a framework and a library? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> A library is a collection of functions\/methods\/classes that you can call from your own code. You’re in charge of the flow of the application; you decide when to call the library. In contrast, with a framework, the flow is determined by the framework itself, invoking your code at specific points (Inversion of Control). Examples include Flask as a framework and NumPy as a library in Python.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Consider the following Python code snippet. Can you identify what’s wrong with it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def add_numbers(a, b):\n <span class=\"hljs-keyword\">return<\/span> a + b\n\n result = add_numbers(<span class=\"hljs-string\">\"5\"<\/span>, <span class=\"hljs-number\">3<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function <code>add_numbers<\/code> is trying to add a string (“5”) and an integer (3) together, which will raise a TypeError in Python. To fix it, one must ensure that both variables are of the same datatype, by converting the string to an integer.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain what a <code>JOIN<\/code> operation is in SQL. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> A <code>JOIN<\/code> operation in SQL is used to combine rows from two or more tables based on a related column between them. The most common types of JOINs include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Look at this SQL query and explain if there is any vulnerability:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> query = <span class=\"hljs-string\">\"SELECT * FROM users WHERE username = '\"<\/span> + username + <span class=\"hljs-string\">\"' AND password = '\"<\/span> + password + <span class=\"hljs-string\">\"';\"<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This query is vulnerable to SQL injection. An attacker can provide malicious input in <code>username<\/code> or <code>password<\/code> to modify the query and potentially access or harm the database. To prevent this, one should use parameterized queries or prepared statements.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Describe the concept of statelessness in RESTful APIs. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Statelessness means that each HTTP request from a client to a server must contain all the information needed to understand and process the request. The server should not store any context between requests, ensuring that each request can be understood in isolation.<\/p>\n\n\n\n<p><strong>Question:<\/strong> What’s the output of the following Python function?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> def mystery_function(a, b=[]):\n b.append(a)\n <span class=\"hljs-keyword\">return<\/span> b\n\n <span class=\"hljs-keyword\">print<\/span>(mystery_function(<span class=\"hljs-number\">1<\/span>))\n <span class=\"hljs-keyword\">print<\/span>(mystery_function(<span class=\"hljs-number\">2<\/span>))<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The output will be:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"JSON \/ JSON with Comments\" data-shcb-language-slug=\"json\"><span><code class=\"hljs language-json shcb-wrap-lines\"> [<span class=\"hljs-number\">1<\/span>]\n [<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">2<\/span>]<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JSON \/ JSON with Comments<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">json<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The mutable default argument (<code>b=[]<\/code>) is a common Python gotcha. The list <code>b<\/code> is created only once when the function is defined, so successive calls to the function reuse the same list.<\/p>\n\n\n\n<p><strong>Question:<\/strong> What is the most Pythonic way to check if a list is empty (considering you are sure the variable to test is a list) ?<\/p>\n\n\n\n<p><strong>Answer:<\/strong> <\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"><span class=\"hljs-keyword\">if<\/span> my_list:\n <span class=\"hljs-comment\"># do something when list is not empty<\/span>\n<span class=\"hljs-keyword\">else<\/span>:\n <span class=\"hljs-comment\"># do something when list is empty<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>It is not necessary to compare it with <code>== []<\/code> or to call <code>len(my_list)<\/code>. When used in a condition, the empty tuples, lists, dictionaries and sets are treated as <code>False<\/code>.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Given this simple express.js middleware, what is its purpose?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-6\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> app.use(<span class=\"hljs-function\">(<span class=\"hljs-params\">req, res, next<\/span>) =><\/span> {\n res.setHeader(<span class=\"hljs-string\">'Cache-Control'<\/span>, <span class=\"hljs-string\">'no-cache'<\/span>);\n next();\n });<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-6\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This middleware sets the <code>Cache-Control<\/code> header to <code>no-cache<\/code> for all responses. It instructs the browser (or caching servers) not to cache the content of the response, ensuring that the client always fetches the latest content from the server.<\/p>\n\n\n\n<p><strong>Question:<\/strong> How can you ensure data integrity in a relational database? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Data integrity can be maintained through the use of constraints such as primary keys, foreign keys, unique constraints, and check constraints. Regular backups, validations, and normalization can also help maintain data integrity.<\/p>\n\n\n\n<p><strong>Question:<\/strong> In the following Node.js code, what issue might arise and how can you fix it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-7\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> <span class=\"hljs-keyword\">const<\/span> fs = <span class=\"hljs-built_in\">require<\/span>(<span class=\"hljs-string\">'fs'<\/span>);\n\n fs.readFile(<span class=\"hljs-string\">'file.txt'<\/span>, <span class=\"hljs-string\">'utf8'<\/span>, (err, data) => {\n <span class=\"hljs-keyword\">if<\/span> (err) <span class=\"hljs-keyword\">throw<\/span> err;\n <span class=\"hljs-built_in\">console<\/span>.log(data);\n });\n\n fs.unlinkSync(<span class=\"hljs-string\">'file.txt'<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-7\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The code is trying to read the content of ‘file.txt’ asynchronously while it’s being deleted synchronously. There’s a race condition; the file might be deleted before the readFile operation completes, leading to an error. To fix it, the deletion should be moved inside the callback of <code>readFile<\/code> to ensure the read operation completes before the file is deleted.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"intermediate-backend-developer-questions\">Intermediate backend developer questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> Describe the differences between horizontal and vertical scaling. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Horizontal scaling<\/strong> means adding more machines to a system. This is often referred to as scaling out. For example, adding more nodes to a distributed database or adding more servers in a load-balanced environment.<\/li>\n\n\n\n<li><strong>Vertical scaling<\/strong> means increasing the resources of an existing machine, such as adding more RAM, CPU, or storage. This is often referred to as scaling up.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Analyze the potential issues with this piece of code handling database connections:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-8\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def get_data(query):\n connection = create_db_connection()\n data = connection.execute(query)\n connection.close()\n <span class=\"hljs-keyword\">return<\/span> data<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-8\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> There are a couple potential issues:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>There’s no error handling. If the connection fails or the query has issues, the code could break.<\/li>\n\n\n\n<li>Each time data is fetched, a new database connection is established and closed. This is resource-intensive and can slow down applications, especially if <code>get_data<\/code> is called frequently.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> What are microservices, and what are their benefits over a monolithic architecture? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Microservices is an architectural style that structures an application as a collection of loosely coupled, independently deployable services. Each service corresponds to a business capability and often has its own database. Benefits include better scalability, flexibility in technology choices for each service, easier maintenance and upgrades, and enhanced fault isolation.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Examine the following endpoint in a Flask application and suggest improvements:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-9\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> @app.route(<span class=\"hljs-string\">'\/users\/<id>'<\/span>, methods=[<span class=\"hljs-string\">'GET'<\/span>])\n def get_user(id):\n user = db.session.query(User).filter_by(id=id).first()\n <span class=\"hljs-keyword\">return<\/span> jsonify(user)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-9\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The function doesn’t handle the case where the user might not be found, potentially leading to a <code>None<\/code> object being passed to <code>jsonify<\/code>. To fix this, Replace the function <code>first<\/code> by the function <code>one<\/code>. Exceptions will be raised and handled by the rest of the code if there is not exactly one record found.<\/li>\n\n\n\n<li>Directly serializing the ORM object may expose sensitive fields. It’s better to use a serialization method or library to ensure only required fields are exposed.<\/li>\n\n\n\n<li>No input validation or type checking for <code>id<\/code>.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> What is the potential bottleneck in the following database query?<\/p>\n\n\n<pre class=\"wp-block-code\"><span><code class=\"hljs shcb-wrap-lines\"> SELECT * FROM orders ORDER BY creation_date DESC LIMIT 10;<\/code><\/span><\/pre>\n\n\n<p><strong>Answer:<\/strong> If there is no index on the <code>creation_date<\/code> column, sorting the table can be resource-intensive, especially as the <code>orders<\/code> table grows in size. To improve this, an index on the <code>creation_date<\/code> column should be considered.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain the concept of eventual consistency. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Eventual consistency refers to a system state where all replicas of data might not be immediately consistent but will become consistent over time. It is a relaxation of the strong consistency model to achieve higher availability and scalability in distributed systems.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Consider the following asynchronous Node.js function. What’s wrong with it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-10\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> <span class=\"hljs-keyword\">async<\/span> <span class=\"hljs-function\"><span class=\"hljs-keyword\">function<\/span> <span class=\"hljs-title\">fetchData<\/span>(<span class=\"hljs-params\"><\/span>) <\/span>{\n <span class=\"hljs-keyword\">let<\/span> data = <span class=\"hljs-keyword\">await<\/span> someAsyncFunction();\n <span class=\"hljs-keyword\">if<\/span> (!data) {\n <span class=\"hljs-keyword\">throw<\/span> <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-built_in\">Error<\/span>(<span class=\"hljs-string\">\"Data not found\"<\/span>);\n }\n <span class=\"hljs-keyword\">return<\/span> processData(data);\n }<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-10\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function lacks error handling for potential failures of <code>someAsyncFunction()<\/code>. A try-catch block should be added around the <code>await<\/code> statement to handle any errors that might arise from that asynchronous call.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Look at this Redis caching function and identify any issues:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-11\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def cache_data(key, value):\n redis_client = redis.StrictRedis(host=<span class=\"hljs-string\">'localhost'<\/span>, port=<span class=\"hljs-number\">6379<\/span>, db=<span class=\"hljs-number\">0<\/span>)\n redis_client.set(key, value)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-11\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function initializes a new Redis connection each time it’s called. This can be inefficient, especially if caching operations are frequent. It’s better to maintain a persistent Redis connection or use a connection pool.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Analyze this Django ORM query for optimization:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-12\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> books = Book.objects.all()\n <span class=\"hljs-keyword\">for<\/span> book in books:\n <span class=\"hljs-keyword\">print<\/span>(book.author.name)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-12\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This code suffers from the “N+1 queries problem”. For each book, a separate query is made to fetch the author’s name, leading to N+1 queries in total (1 to fetch all books + N to fetch the authors). The optimized version would use <code>select_related<\/code>:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-13\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> books = Book.objects.select_related(<span class=\"hljs-string\">'author'<\/span>).all()\n <span class=\"hljs-keyword\">for<\/span> book in books:\n <span class=\"hljs-keyword\">print<\/span>(book.author.name)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-13\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Question:<\/strong> How does a message queue like RabbitMQ or Kafka improve system architecture?<\/p>\n\n\n\n<p><strong>Answer:<\/strong> Message queues decouple components in a system, allowing for asynchronous processing. This means that a component can send a message to the queue without waiting for it to be processed. This has several benefits:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Improved performance and responsiveness, as components don’t block waiting for tasks to complete.<\/li>\n\n\n\n<li>Enhanced system reliability, as the message queue can act as a buffer during high traffic or if a component fails and needs to restart.<\/li>\n\n\n\n<li>Better scalability, as workers can be easily added or removed based on the workload.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"senior-backend-developer-questions\">Senior backend developer questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> Explain the principles and benefits of the Twelve-Factor App methodology. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> The Twelve-Factor App is a set of best practices for building modern, scalable, maintainable software-as-a-service apps. Some key principles include:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Codebase<\/strong>: One codebase tracked in revision control, with many deploys.<\/li>\n\n\n\n<li><strong>Dependencies<\/strong>: Explicitly declare and isolate dependencies.<\/li>\n\n\n\n<li><strong>Config<\/strong>: Store configuration in the environment.<\/li>\n\n\n\n<li><strong>Backing Services<\/strong>: Treat backing services as attached resources.<\/li>\n\n\n\n<li><strong>Build, Release, Run<\/strong>: Strictly separate build and run stages.<\/li>\n\n\n\n<li><strong>Processes<\/strong>: Execute the app as one or more stateless processes.<\/li>\n\n\n\n<li><strong>Port Binding<\/strong>: Export services via port binding.<\/li>\n\n\n\n<li><strong>Concurrency<\/strong>: Scale out via the process model.<\/li>\n\n\n\n<li><strong>Disposability<\/strong>: Maximize robustness with fast startup and graceful shutdown.<\/li>\n\n\n\n<li><strong>Dev\/Prod Parity<\/strong>: Keep development, staging, and production as similar as possible.<\/li>\n\n\n\n<li><strong>Logs<\/strong>: Treat logs as event streams.<\/li>\n\n\n\n<li><strong>Admin Processes<\/strong>: Run admin\/management tasks as one-off processes.<\/li>\n<\/ol>\n\n\n\n<p>Benefits include portability across execution environments, minimized divergence between development and production, and scalability.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain the CAP theorem and its implications in distributed systems design. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><a href=\"https:\/\/en.wikipedia.org\/wiki\/CAP_theorem\" target=\"_blank\" rel=\"noopener\"> The CAP theorem<\/a> states that it’s impossible for a distributed system to simultaneously provide all three of the following guarantees:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Consistency<\/strong>: Every read receives the most recent write.<\/li>\n\n\n\n<li><strong>Availability<\/strong>: Every request receives a (non-error) response, without a guarantee that it contains the most recent version.<\/li>\n\n\n\n<li><strong>Partition tolerance<\/strong>: The system continues to operate despite arbitrary message loss or failure of part of the system.<\/li>\n<\/ul>\n\n\n\n<p>In the face of a network partition, a system must choose between consistency and availability. This theorem guides the design and trade-offs of distributed databases and systems.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Examine the following piece of Python code and identify potential issues related to concurrency:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-14\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> counter = <span class=\"hljs-number\">0<\/span>\n\n def increment_counter():\n <span class=\"hljs-keyword\">global<\/span> counter\n <span class=\"hljs-keyword\">for<\/span> _ in range(<span class=\"hljs-number\">1000000<\/span>):\n counter += <span class=\"hljs-number\">1<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-14\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> If <code>increment_counter<\/code> is called concurrently from multiple threads or processes, there could be race conditions leading to the <code>counter<\/code> not being accurately incremented. A synchronization mechanism like locks or semaphores should be employed to protect the critical section.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Given the following SQL query, how can it be optimized for a large dataset?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-15\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> SELECT orders.id, products.name \n FROM orders \n INNER JOIN products ON orders.product_id = products.id \n WHERE products.category = <span class=\"hljs-string\">'electronics'<\/span>;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-15\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Ensure there are indices on the columns involved in the JOIN operation (<code>orders.product_id<\/code> and <code>products.id<\/code>).<\/li>\n\n\n\n<li>Add an index on <code>products.category<\/code> since it’s used in the WHERE clause.<\/li>\n\n\n\n<li>Consider denormalization or materialized views if this is a frequently executed query.<\/li>\n\n\n\n<li>Think about reworking the database schema. The field <code>products.category<\/code> could be changed to a numeric field and the correspondance between num_category and str_category could be stored in an intermediate table.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Analyze this cache invalidation strategy and suggest improvements:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-16\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def update_product(product):\n db.save(product)\n cache.delete(f<span class=\"hljs-string\">'product-{product.id}'<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-16\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> While the function updates a product in the database and invalidates the cache, a race condition could occur where the cache is repopulated with old data before the database update completes. A better strategy might be to use cache versioning or to update the cache with the new data directly after the database update, ensuring fresh data is always available.<\/p>\n\n\n\n<p><strong>Question:<\/strong> How do you handle versioning in RESTful APIs? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> There are multiple strategies:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>URI Versioning<\/strong>: Include the version in the URI, e.g., <code>\/v1\/users<\/code>.<\/li>\n\n\n\n<li><strong>Header Versioning<\/strong>: Use custom headers, e.g., <code>Accept-version: v1<\/code>.<\/li>\n\n\n\n<li><strong>Accept Header<\/strong>: Use the <code>Accept<\/code> header with a versioned media type, e.g., <code>Accept: application\/json; Version=2<\/code>.<\/li>\n\n\n\n<li><strong>Query Parameter<\/strong>: Include the version in a query parameter, e.g., <code>\/users?version=1<\/code>.<\/li>\n<\/ul>\n\n\n\n<p>It’s essential to choose a method that aligns with the organization’s goals, and it’s also vital to provide proper documentation for clients.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Here’s a simplified code to manage tasks in a queue. Identify potential pitfalls:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-17\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> tasks = []\n\n def add_task(task):\n tasks.append(task)\n\n def process_next_task():\n <span class=\"hljs-keyword\">if<\/span> tasks:\n task = tasks.pop(<span class=\"hljs-number\">0<\/span>)\n <span class=\"hljs-comment\"># process task<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-17\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The list data structure in Python is not efficient for pop operations from the start of the list. This operation is O(n). Using a data structure like <code>deque<\/code> from the <code>collections<\/code> module would be more efficient.<\/li>\n\n\n\n<li>If used in a multithreaded environment, race conditions can occur, leading to tasks being processed multiple times or not at all. Proper synchronization or thread-safe collections should be used.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Consider the following Kafka consumer code snippet. What could be problematic about this?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-18\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> consumer = KafkaConsumer(<span class=\"hljs-string\">'my_topic'<\/span>)\n <span class=\"hljs-keyword\">for<\/span> message <span class=\"hljs-keyword\">in<\/span> consumer:\n process_message(message)\n consumer.commit()<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-18\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The consumer commits after processing each message, which can be inefficient and slow down the message processing rate. Depending on the <code>process_message<\/code> function, failures might result in message loss if a message is committed but not successfully processed. It might be better to batch the commits or use a commit strategy based on time or message count.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Describe the advantages and challenges of transitioning a monolithic application to a microservices architecture. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><br><em>Advantages<\/em>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><em>Scalability<\/em>: Each service can be scaled independently based on its requirements.<\/li>\n\n\n\n<li><em>Flexibility<\/em>: Different services can use different technologies.<\/li>\n\n\n\n<li><em>Maintainability<\/em>: Smaller codebases are easier to understand and maintain.<\/li>\n\n\n\n<li><em>Faster Time to Market<\/em>: Teams can work on different services simultaneously, leading to faster feature releases. <\/li>\n<\/ul>\n\n\n\n<p><em>Challenges<\/em>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><em>Network Complexity<\/em>: Increased inter-service communication can introduce latency and complexity.<\/li>\n\n\n\n<li><em>Data Consistency<\/em>: With services having their own databases, ensuring data consistency can be challenging.<\/li>\n\n\n\n<li><em>Operational Overhead<\/em>: More services mean more things to deploy, monitor, and manage.<\/li>\n\n\n\n<li><em>Service Discovery<\/em>: Services need to discover and communicate with each other.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"more-backend-interview-resources\">More backend interview resources<\/h2>\n\n\n\n<p>For more guides on improving your knowledge of software engineer hiring, we have outlined helpful blog posts below:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/coderpad.io\/blog\/hiring-developers\/hire-back-end-developers\/\">Hire Back-End Developers: 11 strategies and niche job boards<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/blog\/hiring-developers\/software-developers-want-to-leave-their-jobs-is-your-company-ready-to-recruit\/\">Software Developers Want to Leave Their Jobs. Is Your Company Ready to Recruit?<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/blog\/interviewing\/prompt-engineering-for-technical-interview-questions\/\">Prompt Engineering for Technical Interview Questions <\/a><\/li>\n<\/ul>\n\n\n\n<p>Additionally, we offer the following backend framework interview questions:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/nodejs-interview-questions\/\">Node.js<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/ruby-on-rails-interview-questions\/\">Ruby on Rails<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/django-interview-questions\/\">Django<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/spring-interview-questions\/\">Spring<\/a><\/li>\n<\/ul>\n\n\n\n<p><\/p>\n\n\n<section class=\"logo-row-block\">\n <div class=\"inner\">\n <h2 class=\"headline\">1,000 Companies use CoderPad to Screen and Interview Developers<\/h2>\n \n <div class=\"logos logos--grayscale\" >\n <div> <svg class=\"logo logo-spotify\" role=\"img\" viewBox=\"0 0 538 167\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><title>Spotify<\/title><path d=\"M83.743 0C37.494 0 0 37.493 0 83.742c0 46.251 37.494 83.741 83.743 83.741 46.254 0 83.744-37.49 83.744-83.741 0-46.246-37.49-83.738-83.745-83.738L83.743 0zm38.404 120.78a5.217 5.217 0 0 1-7.18 1.73c-19.662-12.01-44.414-14.73-73.564-8.07a5.222 5.222 0 0 1-6.249-3.93 5.213 5.213 0 0 1 3.926-6.25c31.9-7.288 59.263-4.15 81.337 9.34 2.46 1.51 3.24 4.72 1.73 7.18zm10.25-22.802c-1.89 3.072-5.91 4.042-8.98 2.152-22.51-13.836-56.823-17.843-83.448-9.761-3.453 1.043-7.1-.903-8.148-4.35a6.538 6.538 0 0 1 4.354-8.143c30.413-9.228 68.222-4.758 94.072 11.127 3.07 1.89 4.04 5.91 2.15 8.976v-.001zm.88-23.744c-26.99-16.031-71.52-17.505-97.289-9.684-4.138 1.255-8.514-1.081-9.768-5.219a7.835 7.835 0 0 1 5.221-9.771c29.581-8.98 78.756-7.245 109.83 11.202a7.823 7.823 0 0 1 2.74 10.733c-2.2 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xmlns=\"http:\/\/www.w3.org\/2000\/svg\" fill=\"none\" viewBox=\"0 0 206 31\"><title>Chart boost<\/title><g fill=\"currentColor\" clip-path=\"url(#chartboost-a)\"><path d=\"M44.577 18.523c0-7.131 4.357-11.975 11.108-11.975 5.153 0 8.912 3.027 9.777 7.905h-3.06c-.898-3.263-3.36-5.215-6.851-5.215-4.89 0-8.016 3.836-8.016 9.285 0 5.448 2.993 9.284 7.882 9.284 3.593 0 6.087-1.918 6.95-5.215h3.061c-.865 4.878-4.724 7.905-9.977 7.905-6.683.003-10.874-4.775-10.874-11.974m38.345 2.22v9.553h-2.728v-9.383c0-3.566-1.697-5.449-4.624-5.449-3.16 0-5.123 2.08-5.123 6.258v8.58H67.72V6.547h2.727v9.918c.795-2.171 2.728-3.528 5.587-3.528 3.793 0 6.885 2.12 6.885 7.805zm18.795 7.033v2.522h-1.498c-2.26 0-1.973-1.56-2.007-3.242-.837 2.14-3.812 3.444-6.74 3.444-3.724 0-6.252-1.884-6.252-5.011 0-3.43 2.36-5.348 6.82-5.348h4.988v-1.178c0-2.22-1.564-3.565-4.223-3.565-2.395 0-3.992 1.143-4.325 2.894h-2.728c.399-3.364 3.092-5.348 7.184-5.348 4.322 0 6.82 2.186 6.82 6.189v7.502c0 .907.332 1.143 1.096 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id=\"chartboost-a\"><path fill=\"currentColor\" d=\"M.158.5h205v30h-205z\"\/><\/clipPath><\/defs><\/svg>\n\n<\/div>\n <\/div>\n <\/div>\n<\/section>\n\n\n\n<div class=\"wp-block-columns\">\n<div class=\"wp-block-column\"><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img decoding=\"async\" src=\"https:\/\/d2h1bfu6zrdxog.cloudfront.net\/wp-content\/uploads\/2023\/03\/g2-leader-winter-2023.png\" alt=\"\" class=\"wp-image-32119\"\/><\/figure>\n<\/div><\/div>\n\n\n\n<div class=\"wp-block-column\"><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img decoding=\"async\" src=\"https:\/\/d2h1bfu6zrdxog.cloudfront.net\/wp-content\/uploads\/2023\/03\/g2-users-love-us.png\" alt=\"\" class=\"wp-image-32120\"\/><\/figure>\n<\/div><\/div>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"best-interview-practices-for-backend-roles\">Best interview practices for backend roles<\/h2>\n\n\n\n<p>The backend interview process can often be quite diverse, influenced by various elements including the specific engineering role in focus and the applicant’s level of expertise in backend technologies. To enhance the effectiveness of your backend interview questions, consider adopting the following strategies when interacting with potential recruits:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Develop technical queries that reflect actual scenarios encountered in your organization – this approach is not only more engaging for the candidate but also serves as a more accurate gauge of how their skill set aligns with your team’s needs.<\/li>\n\n\n\n<li>Encourage a participatory environment by allowing the candidate to pose questions throughout the process.<\/li>\n\n\n\n<li>Given that backend candidates may sometimes need to collaborate with front-end teams, it is advantageous for them to have a foundational understanding of the principles that govern user interface and user experience design.<\/li>\n<\/ul>\n\n\n\n<p>Furthermore, adhering to standard interview protocols remains crucial during backend interview sessions – adjust the complexity of interview questions based on the candidate’s evolving expertise, provide timely feedback regarding their status in the recruitment process, and offer sufficient opportunities for candidates to discuss the evaluation or delve into the nuances of collaborating with your team.<\/p>\n","protected":false},"parent":0,"menu_order":0,"template":"","class_list":["post-36441","interview-questions","type-interview-questions","status-publish","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/interview-questions\/36441","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/interview-questions"}],"about":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/types\/interview-questions"}],"wp:attachment":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/media?parent=36441"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
2. Store the data from the graphql endpoint into the database and create appropriate models<\/p>\n\n\n\n
3. Write RESTful Create, Read, Update, and Delete endpoints to interact with the database<\/p>\n\n\n\n\t<\/iframe>\n<\/div>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"question-2-shopping-list\"><strong>Question 2: Shopping List<\/strong><\/h3>\n\n\n\n<p>This question tests a candidate’s ability to create model(s) for the data structure, insert hard-coded data into a database, modify tables and fields in a database, and write endpoints to interact with data.<\/p>\n\n\n\n<p><strong>Part 1<\/strong><\/p>\n\n\n\n<p><em>Create a model for the shopping lists and items located in app\/data\/data.ts.<\/em><\/p>\n\n\n\n<p><strong>Part 2<\/strong><\/p>\n\n\n\n<p><em>Store the shopping lists and items located in app\/data\/data.ts in the database.<\/em><\/p>\n\n\n\n<p><strong>Part 3<\/strong><\/p>\n\n\n\n<p><em>Modify the database such that a price field can be stored for each item.<\/em><\/p>\n\n\n\n<p><strong>Part 4<\/strong><\/p>\n\n\n\n<p><em>Multiply the quantity of each item in the shopping lists by two.<\/em><\/p>\n\n\n\n<p><strong>Part 5<\/strong><\/p>\n\n\n\n<p><em>Create API endpoints to dynamically get a list of shopping lists and items.<\/em><\/p>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"assessing-the-candidate\"><strong>Assessing the candidate<\/strong><\/h4>\n\n\n\n<p>The candidate should create models for a shopping list and items. They should then write code to create the tables necessary and insert the data into the tables. Additionally, the candidate can be asked to edit the data in the tables and add additional fields. Finally, endpoints to interact with the data can be created.<\/p>\n\n\n<div\n\tclass=\"sandbox-embed responsive-embed sandbox-embed--full-width\"\n\tstyle=\"padding-top: 85%\"\ndata-block-name=\"coderpad-sandbox-embed\">\n\t<iframe src=\"https:\/\/embed.coderpad.io\/sandbox?question_id=254803u0026use_question_button\" width=\"640\" height=\"544\" loading=\"lazy\" aria-label=\"Try out the CoderPad sandbox\"><\/iframe>\n<\/div>\n\n\n<section class=\"\n\ticon-lists-block\n\t\n\" data-block-name=\"coderpad-icon-lists-block\">\n <div class=\"inner\">\n\n \n <div class=\"lists lists--2\">\n <div class=\"icon-list\">\n <div class=\"top\">\n <div class=\"icon-container\">\n <svg class=\"icon icon-lightning-bolt\" role=\"img\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" fill=\"none\" viewBox=\"0 0 10 14\"><title>lightning bolt<\/title><path fill=\"currentColor\" d=\"M3.608 13.967c.185.079.4.013.508-.158l4.922-7.82a.41.41 0 0 0-.347-.63H5.407L6.628.511a.41.41 0 0 0-.744-.32L.962 8.011a.41.41 0 0 0 .347.63h3.284l-1.221 4.848a.41.41 0 0 0 .236.478Z\"\/><\/svg>\n\n <\/div>\n \n <h3 class=\"title\">Backend skills to assess<\/h3>\n <\/div>\n\n <ul class=\"links\">\n <li>\n <a >Backend frameworks<\/a>\n <\/li>\n <li>\n <a >RESTful API design<\/a>\n <\/li>\n <li>\n <a >Databases and ORMs<\/a>\n <\/li>\n <\/ul>\n <\/div>\n\n <div class=\"icon-list\">\n <div class=\"top\">\n <div class=\"icon-container\">\n <svg class=\"icon icon-briefcase\" role=\"img\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" viewBox=\"0 0 25 26\" fill=\"none\"><title>briefcase<\/title><path fill=\"currentColor\" d=\"M5.469 16.125a5.446 5.446 0 0 1-3.907-1.648v6.335a2.35 2.35 0 0 0 2.344 2.344h17.188a2.35 2.35 0 0 0 2.343-2.343v-6.336a5.446 5.446 0 0 1-3.906 1.648H5.47Z\"\/><path fill=\"currentColor\" d=\"M21.094 5.969h-3.125v-.782a2.344 2.344 0 0 0-2.344-2.343h-6.25a2.344 2.344 0 0 0-2.344 2.344v.78H3.906a2.35 2.35 0 0 0-2.344 2.345v2.343a3.906 3.906 0 0 0 3.907 3.906h2.343V12.22a.781.781 0 1 1 1.563 0v2.344h6.25v-2.344a.781.781 0 1 1 1.563 0v2.344h2.343a3.907 3.907 0 0 0 3.907-3.907V8.312a2.351 2.351 0 0 0-2.344-2.343Zm-12.5-.782a.781.781 0 0 1 .781-.78h6.25a.781.781 0 0 1 .781.78v.782H8.594v-.782Z\"\/><\/svg>\n\n <\/div>\n \n <h3 class=\"title\">Backend job roles<\/h3>\n <\/div>\n\n <ul class=\"links\">\n <li>\n <a >Backend developer<\/a>\n <\/li>\n <li>\n <a >Software engineer<\/a>\n <\/li>\n <li>\n <a >Full-stack developer<\/a>\n <\/li>\n <\/ul>\n <\/div>\n\n <\/div>\n \n <\/div>\n<\/section>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"junior-backend-interview-questions\">Junior backend interview questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> What’s the difference between a framework and a library? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> A library is a collection of functions\/methods\/classes that you can call from your own code. You’re in charge of the flow of the application; you decide when to call the library. In contrast, with a framework, the flow is determined by the framework itself, invoking your code at specific points (Inversion of Control). Examples include Flask as a framework and NumPy as a library in Python.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Consider the following Python code snippet. Can you identify what’s wrong with it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def add_numbers(a, b):\n <span class=\"hljs-keyword\">return<\/span> a + b\n\n result = add_numbers(<span class=\"hljs-string\">\"5\"<\/span>, <span class=\"hljs-number\">3<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function <code>add_numbers<\/code> is trying to add a string (“5”) and an integer (3) together, which will raise a TypeError in Python. To fix it, one must ensure that both variables are of the same datatype, by converting the string to an integer.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain what a <code>JOIN<\/code> operation is in SQL. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> A <code>JOIN<\/code> operation in SQL is used to combine rows from two or more tables based on a related column between them. The most common types of JOINs include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Look at this SQL query and explain if there is any vulnerability:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> query = <span class=\"hljs-string\">\"SELECT * FROM users WHERE username = '\"<\/span> + username + <span class=\"hljs-string\">\"' AND password = '\"<\/span> + password + <span class=\"hljs-string\">\"';\"<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This query is vulnerable to SQL injection. An attacker can provide malicious input in <code>username<\/code> or <code>password<\/code> to modify the query and potentially access or harm the database. To prevent this, one should use parameterized queries or prepared statements.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Describe the concept of statelessness in RESTful APIs. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Statelessness means that each HTTP request from a client to a server must contain all the information needed to understand and process the request. The server should not store any context between requests, ensuring that each request can be understood in isolation.<\/p>\n\n\n\n<p><strong>Question:<\/strong> What’s the output of the following Python function?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> def mystery_function(a, b=[]):\n b.append(a)\n <span class=\"hljs-keyword\">return<\/span> b\n\n <span class=\"hljs-keyword\">print<\/span>(mystery_function(<span class=\"hljs-number\">1<\/span>))\n <span class=\"hljs-keyword\">print<\/span>(mystery_function(<span class=\"hljs-number\">2<\/span>))<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The output will be:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"JSON \/ JSON with Comments\" data-shcb-language-slug=\"json\"><span><code class=\"hljs language-json shcb-wrap-lines\"> [<span class=\"hljs-number\">1<\/span>]\n [<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">2<\/span>]<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JSON \/ JSON with Comments<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">json<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The mutable default argument (<code>b=[]<\/code>) is a common Python gotcha. The list <code>b<\/code> is created only once when the function is defined, so successive calls to the function reuse the same list.<\/p>\n\n\n\n<p><strong>Question:<\/strong> What is the most Pythonic way to check if a list is empty (considering you are sure the variable to test is a list) ?<\/p>\n\n\n\n<p><strong>Answer:<\/strong> <\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"><span class=\"hljs-keyword\">if<\/span> my_list:\n <span class=\"hljs-comment\"># do something when list is not empty<\/span>\n<span class=\"hljs-keyword\">else<\/span>:\n <span class=\"hljs-comment\"># do something when list is empty<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>It is not necessary to compare it with <code>== []<\/code> or to call <code>len(my_list)<\/code>. When used in a condition, the empty tuples, lists, dictionaries and sets are treated as <code>False<\/code>.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Given this simple express.js middleware, what is its purpose?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-6\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> app.use(<span class=\"hljs-function\">(<span class=\"hljs-params\">req, res, next<\/span>) =><\/span> {\n res.setHeader(<span class=\"hljs-string\">'Cache-Control'<\/span>, <span class=\"hljs-string\">'no-cache'<\/span>);\n next();\n });<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-6\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This middleware sets the <code>Cache-Control<\/code> header to <code>no-cache<\/code> for all responses. It instructs the browser (or caching servers) not to cache the content of the response, ensuring that the client always fetches the latest content from the server.<\/p>\n\n\n\n<p><strong>Question:<\/strong> How can you ensure data integrity in a relational database? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Data integrity can be maintained through the use of constraints such as primary keys, foreign keys, unique constraints, and check constraints. Regular backups, validations, and normalization can also help maintain data integrity.<\/p>\n\n\n\n<p><strong>Question:<\/strong> In the following Node.js code, what issue might arise and how can you fix it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-7\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> <span class=\"hljs-keyword\">const<\/span> fs = <span class=\"hljs-built_in\">require<\/span>(<span class=\"hljs-string\">'fs'<\/span>);\n\n fs.readFile(<span class=\"hljs-string\">'file.txt'<\/span>, <span class=\"hljs-string\">'utf8'<\/span>, (err, data) => {\n <span class=\"hljs-keyword\">if<\/span> (err) <span class=\"hljs-keyword\">throw<\/span> err;\n <span class=\"hljs-built_in\">console<\/span>.log(data);\n });\n\n fs.unlinkSync(<span class=\"hljs-string\">'file.txt'<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-7\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The code is trying to read the content of ‘file.txt’ asynchronously while it’s being deleted synchronously. There’s a race condition; the file might be deleted before the readFile operation completes, leading to an error. To fix it, the deletion should be moved inside the callback of <code>readFile<\/code> to ensure the read operation completes before the file is deleted.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"intermediate-backend-developer-questions\">Intermediate backend developer questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> Describe the differences between horizontal and vertical scaling. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Horizontal scaling<\/strong> means adding more machines to a system. This is often referred to as scaling out. For example, adding more nodes to a distributed database or adding more servers in a load-balanced environment.<\/li>\n\n\n\n<li><strong>Vertical scaling<\/strong> means increasing the resources of an existing machine, such as adding more RAM, CPU, or storage. This is often referred to as scaling up.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Analyze the potential issues with this piece of code handling database connections:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-8\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def get_data(query):\n connection = create_db_connection()\n data = connection.execute(query)\n connection.close()\n <span class=\"hljs-keyword\">return<\/span> data<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-8\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> There are a couple potential issues:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>There’s no error handling. If the connection fails or the query has issues, the code could break.<\/li>\n\n\n\n<li>Each time data is fetched, a new database connection is established and closed. This is resource-intensive and can slow down applications, especially if <code>get_data<\/code> is called frequently.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> What are microservices, and what are their benefits over a monolithic architecture? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Microservices is an architectural style that structures an application as a collection of loosely coupled, independently deployable services. Each service corresponds to a business capability and often has its own database. Benefits include better scalability, flexibility in technology choices for each service, easier maintenance and upgrades, and enhanced fault isolation.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Examine the following endpoint in a Flask application and suggest improvements:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-9\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> @app.route(<span class=\"hljs-string\">'\/users\/<id>'<\/span>, methods=[<span class=\"hljs-string\">'GET'<\/span>])\n def get_user(id):\n user = db.session.query(User).filter_by(id=id).first()\n <span class=\"hljs-keyword\">return<\/span> jsonify(user)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-9\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The function doesn’t handle the case where the user might not be found, potentially leading to a <code>None<\/code> object being passed to <code>jsonify<\/code>. To fix this, Replace the function <code>first<\/code> by the function <code>one<\/code>. Exceptions will be raised and handled by the rest of the code if there is not exactly one record found.<\/li>\n\n\n\n<li>Directly serializing the ORM object may expose sensitive fields. It’s better to use a serialization method or library to ensure only required fields are exposed.<\/li>\n\n\n\n<li>No input validation or type checking for <code>id<\/code>.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> What is the potential bottleneck in the following database query?<\/p>\n\n\n<pre class=\"wp-block-code\"><span><code class=\"hljs shcb-wrap-lines\"> SELECT * FROM orders ORDER BY creation_date DESC LIMIT 10;<\/code><\/span><\/pre>\n\n\n<p><strong>Answer:<\/strong> If there is no index on the <code>creation_date<\/code> column, sorting the table can be resource-intensive, especially as the <code>orders<\/code> table grows in size. To improve this, an index on the <code>creation_date<\/code> column should be considered.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain the concept of eventual consistency. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> Eventual consistency refers to a system state where all replicas of data might not be immediately consistent but will become consistent over time. It is a relaxation of the strong consistency model to achieve higher availability and scalability in distributed systems.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Consider the following asynchronous Node.js function. What’s wrong with it?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-10\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> <span class=\"hljs-keyword\">async<\/span> <span class=\"hljs-function\"><span class=\"hljs-keyword\">function<\/span> <span class=\"hljs-title\">fetchData<\/span>(<span class=\"hljs-params\"><\/span>) <\/span>{\n <span class=\"hljs-keyword\">let<\/span> data = <span class=\"hljs-keyword\">await<\/span> someAsyncFunction();\n <span class=\"hljs-keyword\">if<\/span> (!data) {\n <span class=\"hljs-keyword\">throw<\/span> <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-built_in\">Error<\/span>(<span class=\"hljs-string\">\"Data not found\"<\/span>);\n }\n <span class=\"hljs-keyword\">return<\/span> processData(data);\n }<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-10\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function lacks error handling for potential failures of <code>someAsyncFunction()<\/code>. A try-catch block should be added around the <code>await<\/code> statement to handle any errors that might arise from that asynchronous call.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Look at this Redis caching function and identify any issues:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-11\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def cache_data(key, value):\n redis_client = redis.StrictRedis(host=<span class=\"hljs-string\">'localhost'<\/span>, port=<span class=\"hljs-number\">6379<\/span>, db=<span class=\"hljs-number\">0<\/span>)\n redis_client.set(key, value)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-11\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The function initializes a new Redis connection each time it’s called. This can be inefficient, especially if caching operations are frequent. It’s better to maintain a persistent Redis connection or use a connection pool.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Analyze this Django ORM query for optimization:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-12\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> books = Book.objects.all()\n <span class=\"hljs-keyword\">for<\/span> book in books:\n <span class=\"hljs-keyword\">print<\/span>(book.author.name)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-12\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> This code suffers from the “N+1 queries problem”. For each book, a separate query is made to fetch the author’s name, leading to N+1 queries in total (1 to fetch all books + N to fetch the authors). The optimized version would use <code>select_related<\/code>:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-13\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> books = Book.objects.select_related(<span class=\"hljs-string\">'author'<\/span>).all()\n <span class=\"hljs-keyword\">for<\/span> book in books:\n <span class=\"hljs-keyword\">print<\/span>(book.author.name)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-13\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Question:<\/strong> How does a message queue like RabbitMQ or Kafka improve system architecture?<\/p>\n\n\n\n<p><strong>Answer:<\/strong> Message queues decouple components in a system, allowing for asynchronous processing. This means that a component can send a message to the queue without waiting for it to be processed. This has several benefits:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Improved performance and responsiveness, as components don’t block waiting for tasks to complete.<\/li>\n\n\n\n<li>Enhanced system reliability, as the message queue can act as a buffer during high traffic or if a component fails and needs to restart.<\/li>\n\n\n\n<li>Better scalability, as workers can be easily added or removed based on the workload.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"senior-backend-developer-questions\">Senior backend developer questions<\/h2>\n\n\n\n<p><strong>Question:<\/strong> Explain the principles and benefits of the Twelve-Factor App methodology. <\/p>\n\n\n\n<p><strong>Answer:<\/strong> The Twelve-Factor App is a set of best practices for building modern, scalable, maintainable software-as-a-service apps. Some key principles include:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Codebase<\/strong>: One codebase tracked in revision control, with many deploys.<\/li>\n\n\n\n<li><strong>Dependencies<\/strong>: Explicitly declare and isolate dependencies.<\/li>\n\n\n\n<li><strong>Config<\/strong>: Store configuration in the environment.<\/li>\n\n\n\n<li><strong>Backing Services<\/strong>: Treat backing services as attached resources.<\/li>\n\n\n\n<li><strong>Build, Release, Run<\/strong>: Strictly separate build and run stages.<\/li>\n\n\n\n<li><strong>Processes<\/strong>: Execute the app as one or more stateless processes.<\/li>\n\n\n\n<li><strong>Port Binding<\/strong>: Export services via port binding.<\/li>\n\n\n\n<li><strong>Concurrency<\/strong>: Scale out via the process model.<\/li>\n\n\n\n<li><strong>Disposability<\/strong>: Maximize robustness with fast startup and graceful shutdown.<\/li>\n\n\n\n<li><strong>Dev\/Prod Parity<\/strong>: Keep development, staging, and production as similar as possible.<\/li>\n\n\n\n<li><strong>Logs<\/strong>: Treat logs as event streams.<\/li>\n\n\n\n<li><strong>Admin Processes<\/strong>: Run admin\/management tasks as one-off processes.<\/li>\n<\/ol>\n\n\n\n<p>Benefits include portability across execution environments, minimized divergence between development and production, and scalability.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Explain the CAP theorem and its implications in distributed systems design. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><a href=\"https:\/\/en.wikipedia.org\/wiki\/CAP_theorem\" target=\"_blank\" rel=\"noopener\"> The CAP theorem<\/a> states that it’s impossible for a distributed system to simultaneously provide all three of the following guarantees:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Consistency<\/strong>: Every read receives the most recent write.<\/li>\n\n\n\n<li><strong>Availability<\/strong>: Every request receives a (non-error) response, without a guarantee that it contains the most recent version.<\/li>\n\n\n\n<li><strong>Partition tolerance<\/strong>: The system continues to operate despite arbitrary message loss or failure of part of the system.<\/li>\n<\/ul>\n\n\n\n<p>In the face of a network partition, a system must choose between consistency and availability. This theorem guides the design and trade-offs of distributed databases and systems.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Examine the following piece of Python code and identify potential issues related to concurrency:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-14\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> counter = <span class=\"hljs-number\">0<\/span>\n\n def increment_counter():\n <span class=\"hljs-keyword\">global<\/span> counter\n <span class=\"hljs-keyword\">for<\/span> _ in range(<span class=\"hljs-number\">1000000<\/span>):\n counter += <span class=\"hljs-number\">1<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-14\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> If <code>increment_counter<\/code> is called concurrently from multiple threads or processes, there could be race conditions leading to the <code>counter<\/code> not being accurately incremented. A synchronization mechanism like locks or semaphores should be employed to protect the critical section.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Given the following SQL query, how can it be optimized for a large dataset?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-15\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> SELECT orders.id, products.name \n FROM orders \n INNER JOIN products ON orders.product_id = products.id \n WHERE products.category = <span class=\"hljs-string\">'electronics'<\/span>;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-15\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Ensure there are indices on the columns involved in the JOIN operation (<code>orders.product_id<\/code> and <code>products.id<\/code>).<\/li>\n\n\n\n<li>Add an index on <code>products.category<\/code> since it’s used in the WHERE clause.<\/li>\n\n\n\n<li>Consider denormalization or materialized views if this is a frequently executed query.<\/li>\n\n\n\n<li>Think about reworking the database schema. The field <code>products.category<\/code> could be changed to a numeric field and the correspondance between num_category and str_category could be stored in an intermediate table.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Analyze this cache invalidation strategy and suggest improvements:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-16\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> def update_product(product):\n db.save(product)\n cache.delete(f<span class=\"hljs-string\">'product-{product.id}'<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-16\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> While the function updates a product in the database and invalidates the cache, a race condition could occur where the cache is repopulated with old data before the database update completes. A better strategy might be to use cache versioning or to update the cache with the new data directly after the database update, ensuring fresh data is always available.<\/p>\n\n\n\n<p><strong>Question:<\/strong> How do you handle versioning in RESTful APIs? <\/p>\n\n\n\n<p><strong>Answer:<\/strong> There are multiple strategies:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>URI Versioning<\/strong>: Include the version in the URI, e.g., <code>\/v1\/users<\/code>.<\/li>\n\n\n\n<li><strong>Header Versioning<\/strong>: Use custom headers, e.g., <code>Accept-version: v1<\/code>.<\/li>\n\n\n\n<li><strong>Accept Header<\/strong>: Use the <code>Accept<\/code> header with a versioned media type, e.g., <code>Accept: application\/json; Version=2<\/code>.<\/li>\n\n\n\n<li><strong>Query Parameter<\/strong>: Include the version in a query parameter, e.g., <code>\/users?version=1<\/code>.<\/li>\n<\/ul>\n\n\n\n<p>It’s essential to choose a method that aligns with the organization’s goals, and it’s also vital to provide proper documentation for clients.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Here’s a simplified code to manage tasks in a queue. Identify potential pitfalls:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-17\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php shcb-wrap-lines\"> tasks = []\n\n def add_task(task):\n tasks.append(task)\n\n def process_next_task():\n <span class=\"hljs-keyword\">if<\/span> tasks:\n task = tasks.pop(<span class=\"hljs-number\">0<\/span>)\n <span class=\"hljs-comment\"># process task<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-17\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The list data structure in Python is not efficient for pop operations from the start of the list. This operation is O(n). Using a data structure like <code>deque<\/code> from the <code>collections<\/code> module would be more efficient.<\/li>\n\n\n\n<li>If used in a multithreaded environment, race conditions can occur, leading to tasks being processed multiple times or not at all. Proper synchronization or thread-safe collections should be used.<\/li>\n<\/ul>\n\n\n\n<p><strong>Question:<\/strong> Consider the following Kafka consumer code snippet. What could be problematic about this?<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-18\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript shcb-wrap-lines\"> consumer = KafkaConsumer(<span class=\"hljs-string\">'my_topic'<\/span>)\n <span class=\"hljs-keyword\">for<\/span> message <span class=\"hljs-keyword\">in<\/span> consumer:\n process_message(message)\n consumer.commit()<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-18\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><strong>Answer:<\/strong> The consumer commits after processing each message, which can be inefficient and slow down the message processing rate. Depending on the <code>process_message<\/code> function, failures might result in message loss if a message is committed but not successfully processed. It might be better to batch the commits or use a commit strategy based on time or message count.<\/p>\n\n\n\n<p><strong>Question:<\/strong> Describe the advantages and challenges of transitioning a monolithic application to a microservices architecture. <\/p>\n\n\n\n<p><strong>Answer:<\/strong><br><em>Advantages<\/em>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><em>Scalability<\/em>: Each service can be scaled independently based on its requirements.<\/li>\n\n\n\n<li><em>Flexibility<\/em>: Different services can use different technologies.<\/li>\n\n\n\n<li><em>Maintainability<\/em>: Smaller codebases are easier to understand and maintain.<\/li>\n\n\n\n<li><em>Faster Time to Market<\/em>: Teams can work on different services simultaneously, leading to faster feature releases. <\/li>\n<\/ul>\n\n\n\n<p><em>Challenges<\/em>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><em>Network Complexity<\/em>: Increased inter-service communication can introduce latency and complexity.<\/li>\n\n\n\n<li><em>Data Consistency<\/em>: With services having their own databases, ensuring data consistency can be challenging.<\/li>\n\n\n\n<li><em>Operational Overhead<\/em>: More services mean more things to deploy, monitor, and manage.<\/li>\n\n\n\n<li><em>Service Discovery<\/em>: Services need to discover and communicate with each other.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"more-backend-interview-resources\">More backend interview resources<\/h2>\n\n\n\n<p>For more guides on improving your knowledge of software engineer hiring, we have outlined helpful blog posts below:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/coderpad.io\/blog\/hiring-developers\/hire-back-end-developers\/\">Hire Back-End Developers: 11 strategies and niche job boards<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/blog\/hiring-developers\/software-developers-want-to-leave-their-jobs-is-your-company-ready-to-recruit\/\">Software Developers Want to Leave Their Jobs. Is Your Company Ready to Recruit?<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/blog\/interviewing\/prompt-engineering-for-technical-interview-questions\/\">Prompt Engineering for Technical Interview Questions <\/a><\/li>\n<\/ul>\n\n\n\n<p>Additionally, we offer the following backend framework interview questions:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/nodejs-interview-questions\/\">Node.js<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/ruby-on-rails-interview-questions\/\">Ruby on Rails<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/django-interview-questions\/\">Django<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/coderpad.io\/interview-questions\/spring-interview-questions\/\">Spring<\/a><\/li>\n<\/ul>\n\n\n\n<p><\/p>\n\n\n<section class=\"logo-row-block\">\n <div class=\"inner\">\n <h2 class=\"headline\">1,000 Companies use CoderPad to Screen and Interview 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id=\"chartboost-a\"><path fill=\"currentColor\" d=\"M.158.5h205v30h-205z\"\/><\/clipPath><\/defs><\/svg>\n\n<\/div>\n <\/div>\n <\/div>\n<\/section>\n\n\n\n<div class=\"wp-block-columns\">\n<div class=\"wp-block-column\"><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img decoding=\"async\" src=\"https:\/\/d2h1bfu6zrdxog.cloudfront.net\/wp-content\/uploads\/2023\/03\/g2-leader-winter-2023.png\" alt=\"\" class=\"wp-image-32119\"\/><\/figure>\n<\/div><\/div>\n\n\n\n<div class=\"wp-block-column\"><div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img decoding=\"async\" src=\"https:\/\/d2h1bfu6zrdxog.cloudfront.net\/wp-content\/uploads\/2023\/03\/g2-users-love-us.png\" alt=\"\" class=\"wp-image-32120\"\/><\/figure>\n<\/div><\/div>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"best-interview-practices-for-backend-roles\">Best interview practices for backend roles<\/h2>\n\n\n\n<p>The backend interview process can often be quite diverse, influenced by various elements including the specific engineering role in focus and the applicant’s level of expertise in backend technologies. To enhance the effectiveness of your backend interview questions, consider adopting the following strategies when interacting with potential recruits:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Develop technical queries that reflect actual scenarios encountered in your organization – this approach is not only more engaging for the candidate but also serves as a more accurate gauge of how their skill set aligns with your team’s needs.<\/li>\n\n\n\n<li>Encourage a participatory environment by allowing the candidate to pose questions throughout the process.<\/li>\n\n\n\n<li>Given that backend candidates may sometimes need to collaborate with front-end teams, it is advantageous for them to have a foundational understanding of the principles that govern user interface and user experience design.<\/li>\n<\/ul>\n\n\n\n<p>Furthermore, adhering to standard interview protocols remains crucial during backend interview sessions – adjust the complexity of interview questions based on the candidate’s evolving expertise, provide timely feedback regarding their status in the recruitment process, and offer sufficient opportunities for candidates to discuss the evaluation or delve into the nuances of collaborating with your team.<\/p>\n","protected":false},"parent":0,"menu_order":0,"template":"","class_list":["post-36441","interview-questions","type-interview-questions","status-publish","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/interview-questions\/36441","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/interview-questions"}],"about":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/types\/interview-questions"}],"wp:attachment":[{"href":"https:\/\/coderpad.io\/wp-json\/wp\/v2\/media?parent=36441"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}