Backend Development Interview Questions

Question	Answer
What is backend development?	Backend development involves building and maintaining the server-side of a web application. It includes database interactions, API design, and server-side logic that powers the frontend.
What is an API?	An API (Application Programming Interface) allows communication between different software systems. In backend development, APIs are used to allow the frontend to interact with the server-side data.
What is a server-side framework?	A server-side framework is a collection of pre-written code that helps developers build the backend of a web application faster. Examples include Node.js, Django, and Ruby on Rails.
What is REST API?	REST (Representational State Transfer) is an architectural style used for designing networked applications. It uses stateless communication and standard HTTP methods like GET, POST, PUT, DELETE to perform operations.
What is the difference between SQL and NoSQL databases?	SQL databases are relational, use structured data, and rely on SQL queries for data manipulation. NoSQL databases are non-relational, store data in a variety of formats, and provide more flexibility for unstructured data.
What is middleware in backend development?	Middleware is software that connects different applications or services. In backend development, it acts as a bridge between the server and database, handling requests, responses, and other operations like authentication.
What is the importance of authentication and authorization?	Authentication ensures that users are who they claim to be, typically through usernames and passwords. Authorization controls access to resources based on user roles, ensuring security and proper access control.
What is MVC architecture?	MVC stands for Model-View-Controller. It is an architectural pattern used to separate concerns in web applications, dividing the app into three interconnected components: the model (data), view (UI), and controller (logic).
What is the role of a backend developer?	A backend developer is responsible for building and maintaining the server-side components of web applications. This includes writing APIs, integrating databases, and ensuring that data flows correctly between frontend and backend systems.
What is Node.js?	Node.js is a JavaScript runtime built on Chrome's V8 JavaScript engine, allowing developers to run JavaScript on the server-side. It is commonly used for building fast, scalable web applications and APIs.
What is a relational database?	A relational database stores data in tables with predefined schemas. The data is organized into rows and columns, and relationships between tables are defined using keys. Examples include MySQL, PostgreSQL, and SQLite.
What is the purpose of a web server?	A web server is software that handles incoming HTTP requests from clients (browsers) and responds with data. It processes requests for web pages, images, APIs, and other resources.
What is an ORM?	ORM (Object-Relational Mapping) is a technique that allows developers to interact with a database using object-oriented programming languages instead of writing SQL queries. Examples include Sequelize (for Node.js) and Django ORM (for Python).
What is the purpose of session management?	Session management ensures that user data (such as login credentials) is stored and maintained throughout a user's interaction with the application. It helps in creating personalized experiences and managing user states.
What is a load balancer?	A load balancer distributes incoming network traffic across multiple servers to ensure no single server is overwhelmed, improving scalability and reliability.
What is a microservices architecture?	Microservices is an architectural style where an application is developed as a collection of loosely coupled services, each responsible for a specific function, and deployed independently.
What are WebSockets?	WebSockets provide full-duplex communication channels over a single TCP connection, allowing real-time, bidirectional data transfer between the client and server.
What is GraphQL?	GraphQL is a query language for APIs and a runtime for executing those queries by using a type system you define for your data. It allows clients to request exactly the data they need.
What is CORS (Cross-Origin Resource Sharing)?	CORS is a security feature implemented by web browsers to allow or restrict web applications from making requests to domains other than the one that served the web page.
What is OAuth 2.0?	OAuth 2.0 is an authorization framework that allows third-party applications to securely access user data without exposing their credentials, using access tokens.
What is JWT (JSON Web Token)?	JWT is a compact and self-contained way to represent information between two parties as a JSON object. It's commonly used for authentication and authorization purposes.
What is serverless architecture?	Serverless architecture allows developers to build and run applications without managing servers, relying on cloud services like AWS Lambda or Azure Functions for running code in response to events.
What is API Gateway?	An API Gateway is a server that acts as an entry point for client requests to microservices, handling tasks like routing, authentication, and rate limiting.
What is caching in backend development?	Caching is the process of storing frequently accessed data in a temporary storage area (cache) to reduce latency and improve application performance by avoiding repeated calculations or database queries.
What are environment variables?	Environment variables are configuration settings stored outside an application that provide environment-specific information such as database credentials, API keys, and app settings.
What is the difference between PUT and PATCH HTTP methods?	PUT is used to update or replace a resource completely, while PATCH is used to partially update a resource without changing the entire resource.
What is the use of webhooks in backend systems?	Webhooks are HTTP callbacks that allow one system to notify another system of events in real-time, enabling real-time data synchronization between systems.
What are the common HTTP status codes and what do they mean?	Some common HTTP status codes are: 200 (OK), 404 (Not Found), 500 (Internal Server Error), and 403 (Forbidden). These codes represent the result of an HTTP request.
What is the importance of database indexing?	Indexing improves the speed of data retrieval operations in databases by creating an efficient lookup structure, but it can slightly reduce performance during write operations.
What are the benefits of containerization in backend development?	Containerization allows applications and their dependencies to be bundled together into a container, ensuring consistency across different environments and simplifying deployment and scalability.
What is continuous integration/continuous deployment (CI/CD)?	CI/CD is a set of practices that enable automated testing, building, and deployment of code changes. CI ensures code is frequently merged and tested, while CD ensures code is deployed automatically to production.
What is the difference between horizontal and vertical scaling?	Horizontal scaling involves adding more machines or instances to a system, while vertical scaling involves upgrading the resources (CPU, RAM) of an existing machine or instance.
What is RESTful API?	RESTful API is an architectural style for designing networked applications. It uses HTTP requests to access and manipulate resources, following REST principles like statelessness, uniform interface, and client-server architecture.
What is SQL injection?	SQL injection is a code injection technique that exploits vulnerabilities in an application's software by inserting malicious SQL queries into input fields, potentially allowing unauthorized access to a database.
What is the difference between SQL and NoSQL databases?	SQL databases are relational and use structured query language for defining and managing data, while NoSQL databases are non-relational and can store unstructured or semi-structured data, offering scalability and flexibility.
What is the purpose of an ORM (Object-Relational Mapping)?	ORM is a programming technique that allows developers to interact with a relational database using object-oriented programming languages, mapping database tables to classes and rows to objects.
What is a middleware in backend development?	Middleware is software that connects different applications or services by handling requests and responses, performing tasks like authentication, logging, and request modification.
What are the differences between a GET and POST request?	A GET request retrieves data from the server and appends parameters in the URL, while a POST request sends data to the server, typically in the body of the request, often used for creating or updating data.
What is database normalization?	Database normalization is the process of organizing data in a database to reduce redundancy and improve data integrity by dividing large tables into smaller ones and establishing relationships between them.
What is an API rate limit?	API rate limiting is a technique used to control the number of API requests a client can make within a specific time frame, preventing abuse and ensuring fair usage of resources.
What is a database transaction?	A database transaction is a sequence of operations performed as a single unit of work. Transactions ensure that all operations are completed successfully or rolled back in case of an error, maintaining data consistency.
What is the difference between a primary key and a foreign key?	A primary key uniquely identifies each record in a database table, while a foreign key is a field in one table that links to the primary key of another table, creating a relationship between them.
What is the purpose of a reverse proxy?	A reverse proxy acts as an intermediary between clients and servers, routing client requests to the appropriate backend server. It is used for load balancing, caching, and enhancing security.
What is JWT Authentication?	JWT (JSON Web Token) Authentication is a method for securely transmitting information between parties as a JSON object. It is often used for authenticating API requests by sending tokens that contain user data.
What is a serverless function?	A serverless function is a cloud-based execution model where code runs in response to events without the need to manage servers. It automatically scales based on demand, and users are billed only for actual execution time.
What is the purpose of a web framework?	A web framework provides a set of tools, libraries, and guidelines that make it easier to build web applications, including routing, database access, security features, and templating.
What is horizontal scaling?	Horizontal scaling refers to adding more instances (servers) to a system to distribute the load. It contrasts with vertical scaling, which involves upgrading the hardware of a single server.
What is the role of a web server?	A web server is software that serves web pages to users by handling HTTP requests, processing them, and returning appropriate responses, such as HTML, CSS, or JavaScript files.
What is the purpose of SSL/TLS in backend development?	SSL (Secure Sockets Layer) and TLS (Transport Layer Security) are cryptographic protocols used to encrypt communication between clients and servers, ensuring secure data transmission over the internet.
What is a container in backend development?	A container is a lightweight, portable unit that packages an application and its dependencies, ensuring it can run consistently across different environments, such as development, staging, and production.
What are the differences between monolithic and microservices architecture?	Monolithic architecture involves building a single unified application, while microservices architecture divides the application into smaller, independently deployable services, each responsible for a specific function.
What is the role of a load balancer?	A load balancer distributes incoming network traffic across multiple servers to ensure no single server becomes overwhelmed, improving reliability and performance.
What is the difference between synchronous and asynchronous communication?	Synchronous communication requires the sender and receiver to operate at the same time (blocking), while asynchronous communication allows the sender and receiver to operate independently (non-blocking).
What is a web API?	A web API (Application Programming Interface) allows different software systems to communicate over the web using protocols like HTTP, enabling interaction between frontend and backend services.
What is the purpose of caching in backend development?	Caching stores frequently accessed data in memory or a fast storage system to reduce latency and improve application performance by avoiding repeated computations or database queries.
What is a session in web development?	A session is a way to store data for a user across multiple requests during their interaction with a web application, commonly used for tracking user login states.
What is OAuth?	OAuth (Open Authorization) is an open standard for token-based authentication and authorization, allowing third-party applications to access user data without exposing sensitive credentials.
What is the difference between PUT and PATCH HTTP methods?	PUT is used to update or replace an entire resource, while PATCH is used to partially update a resource, sending only the data that needs modification.
What is a REST API status code?	A REST API status code is a 3-digit number returned by a server to indicate the outcome of an HTTP request. Examples include 200 (OK), 404 (Not Found), and 500 (Internal Server Error).
What is an SQL query?	An SQL query is a command used to interact with a database to retrieve, insert, update, or delete data. Examples include SELECT, INSERT, UPDATE, and DELETE.
What is the difference between DELETE and TRUNCATE in SQL?	DELETE removes records from a table based on a condition and can be rolled back, while TRUNCATE removes all records from a table without the possibility of rollback.
What is the purpose of a CDN (Content Delivery Network)?	A CDN is a network of geographically distributed servers that deliver web content (like images, videos, and scripts) to users based on their location, improving load times and reducing server load.
What is a message queue?	A message queue is a communication protocol that enables asynchronous communication between different parts of an application, where messages are stored temporarily and processed by consumers.
What is the purpose of an API gateway?	An API gateway acts as an entry point for client requests to backend services, managing tasks like authentication, routing, rate limiting, and load balancing.
What is the difference between vertical and horizontal scaling?	Vertical scaling involves adding resources (CPU, RAM) to a single server, while horizontal scaling involves adding more servers to distribute the load across multiple machines.
What is a transaction in SQL?	A transaction is a set of SQL operations that are executed as a single unit. Transactions ensure data integrity and allow for rollback in case of an error, adhering to the ACID properties (Atomicity, Consistency, Isolation, Durability).
What is the difference between SELECT and SELECT DISTINCT in SQL?	SELECT retrieves all records from a table, including duplicates, while SELECT DISTINCT returns only unique records, removing duplicates.
What is a database index?	A database index is a data structure that improves the speed of data retrieval operations on a database table by allowing quick lookups based on indexed columns.
What is a database foreign key?	A foreign key is a field in a database table that creates a relationship between two tables, referring to the primary key of another table.
What is a microservice architecture?	Microservice architecture is a design style where an application is broken down into small, loosely coupled services, each focused on a specific business function, allowing for easier scaling and deployment.