Backend Interview Questions & Answers

Backend Interview Questions & Answers

🔹 1. What is Backend Development?

Backend development refers to the server-side of web applications that handles data storage, business logic, authentication, and APIs.

🔹 2. What does a backend developer do?

A backend developer:

  • Builds APIs
  • Manages databases
  • Handles authentication
  • Writes server-side logic
  • Ensures performance and security

🔹 3. What are backend technologies?

Common backend technologies:

  • Node.js
  • Java
  • Python
  • PHP
  • Ruby
  • Go

🔹 4. What is a server?

A server is a system that processes requests and sends responses to clients.

🔹 5. What is API?

API (Application Programming Interface) allows communication between frontend and backend.

🔹 6. What is REST API?

REST API is a web service that uses HTTP methods:

  • GET
  • POST
  • PUT
  • DELETE

🔹 7. What is JSON?

JSON is a lightweight format used to exchange data between client and server.

🔹 8. What is HTTP?

HTTP is a protocol used for communication between browser and server.

🔹 9. Difference between HTTP and HTTPS?

HTTPHTTPS
Not secureSecure (SSL encrypted)

🔹 10. What is authentication?

Authentication verifies who the user is (login system).

🔹 11. What is authorization?

Authorization checks what the user can access.

🔹 12. What is JWT?

JWT (JSON Web Token) is used for secure authentication.

🔹 13. What is session?

Session stores user data on server after login.

🔹 14. What is cookie?

Cookies store user data in browser.

🔹 15. Difference between session and cookie?

SessionCookie
Stored on serverStored on browser
More secureLess secure

🔹 16. What is database?

A database is used to store and manage data.

🔹 17. Types of databases?

  • SQL (MySQL, PostgreSQL)
  • NoSQL (MongoDB)

🔹 18. Difference between SQL and NoSQL?

SQLNoSQL
Structured dataUnstructured data
TablesDocuments

🔹 19. What is CRUD?

CRUD operations:

  • Create
  • Read
  • Update
  • Delete

🔹 20. What is middleware?

Middleware is a function that runs between request and response.

🔹 21. What is Express.js?

Express is a Node.js framework for building APIs.

🔹 22. What is Node.js?

Node.js is a runtime environment for executing JavaScript on server.

🔹 23. What is backend framework?

A framework provides tools to build backend applications faster.

🔹 24. What is scalability?

Ability of system to handle increasing traffic.

🔹 25. What is performance optimization?

Improving speed and efficiency of backend system.

🔹 API & System Design

26. What is REST architecture?

REST is a design style for APIs using HTTP.

27. What is SOAP API?

SOAP is a protocol-based web service (older than REST).

28. What is microservices?

Architecture where app is divided into small independent services.

29. Monolithic vs microservices?

MonolithicMicroservices
Single systemMultiple services
Hard to scaleEasy to scale

30. What is load balancing?

Distributes traffic across multiple servers.

31. What is caching?

Stores frequently used data for faster access.

32. What is CDN?

Content Delivery Network for faster content delivery.

33. What is API testing?

Testing API functionality using tools like Postman.

34. What is rate limiting?

Restricting number of requests a user can make.

35. What is versioning in API?

Maintaining multiple versions of API.

🔹 Database Questions

36. What is primary key?

Unique identifier for table rows.

37. What is foreign key?

Links two tables together.

38. What is indexing?

Improves database query speed.

39. What is normalization?

Process of reducing data redundancy.

40. What is denormalization?

Adding redundancy to improve performance.

41. What is aggregation?

Process of combining data (MongoDB).

42. What is replication?

Copying database to multiple servers.

43. What is sharding?

Splitting database across servers.

44. What is backup?

Copy of data for recovery.

45. What is query optimization?

Improving speed of database queries.

🔹 Security Questions

46. What is encryption?

Converting data into secure format.

47. What is hashing?

One-way encryption of data.

48. What is SQL injection?

Security attack using malicious SQL queries.

49. What is XSS?

Cross-site scripting attack.

50. How to secure backend?

  • Use authentication
  • Encrypt data
  • Validate inputs
  • Use HTTPS
  • Use JWT

🔹 Coding & Practical Questions

51. Build REST API?

Use Node.js + Express + database.

52. Create login system?

Use authentication + JWT tokens.

53. How does backend connect to frontend?

Using APIs (REST or GraphQL).

54. How to deploy backend?

Using:

  • AWS
  • Heroku
  • Vercel
  • DigitalOcean

55. What is environment variable?

Stores sensitive configuration data.

🔹 HR Questions

56. Tell me about yourself?

Explain skills, projects, backend experience.

57. Why backend development?

Because it powers logic and data systems.

58. What are your strengths?

Problem-solving, API design, database handling.

59. Describe your project?

Explain backend architecture clearly.

60. Why should we hire you?

Mention skills, experience, and confidence.