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Backend Developer Interview Questions and Answers

Backend interviews cover APIs, databases, concurrency, distributed systems and system design, plus coding rounds and behavioural questions. Spring Boot and microservices questions are common in Java roles in India.

Below are 122 questions asked in backend developer interviews, each with a sample answer and tips. Read the answer, then practise it out loud: InterviewGuru's AI mock practice scores your spoken or typed answer out of 10 and shows what to improve.

🎯 What interviewers look for
  • API design: resources, idempotency, pagination, versioning and error handling
  • Databases: indexing, transactions and isolation, when to use SQL or NoSQL, and how to scale reads and writes
  • Reliability: retries with backoff, timeouts, queues, rate limiting and graceful failure
  • System design with numbers and named trade-offs (consistency, latency, cost)
  • Debugging and on-call stories: how you found a production issue and prevented it from coming back
Behavioral (14)
Tell me about a time you had to deal with an ambiguous project requirement.Medium Describe a situation where a production outage occurred on your watch. How did you respond?Hard Give an example of a time you received critical constructive feedback. How did you handle it?Easy Describe a project where you had to learn a completely new technology under tight deadlines.Medium Tell me about a time you identified a technical debt problem and successfully advocated to fix it.Medium Tell me about a time you had to balance feature delivery speed against code quality.Easy Give an example of a time you went above and beyond your defined job responsibilities.Easy Tell me about a complex bug that took days to track down. How did you diagnose and solve it?Hard Describe a time you had to make a technical decision without full data or clarity.Hard Tell me about a time you handled a disagreement within your own engineering squad.Medium Tell me about a time you optimized an application's performance. What was your approach?Medium Describe a situation where you had to maintain high standards under extreme pressure.Medium Tell me about a time you had to sunset or deprecate a legacy system.Hard Describe a time you proactively prevented a customer-facing issue before it occurred.Easy
Leadership (5)
How do you align an engineering team when members have conflicting architectural viewpoints?Hard Tell me about a time you led a strategic technical migration without disrupting ongoing business operations.Hard Tell me about a time you took a calculated risk that paid off for your team.Medium How do you handle technical debt when expanding rapidly to capture market share?Hard Describe a time you built consensus around a controversial decision that affected multiple squads.Hard
Culture Fit (5)
Why do you want to work at our company specifically?Easy How do you stay updated with emerging technologies and decide when to adopt them?Easy Tell me about a time you admitted a mistake openly at work.Easy What does taking 'extreme ownership' of a feature mean to you in practice?Medium How do you handle repetitive or unglamorous engineering tasks that need to get done?Easy
Teamwork (6)
Describe a situation where you had to rely on a teammate's work that was delivered late. How did you handle it?Medium How do you handle code reviews when you disagree with an approach suggested by a senior teammate?Medium Tell me about a time you helped resolve a bottleneck in another team's workflow.Easy Tell me about a time you gave up ownership of an idea or project to support a better team solution.Medium Describe a time you stepped up to resolve an emergency when the primary owner was unavailable.Medium How do you build trust with a new engineering team when joining as a senior or lead engineer?Medium
HR Screening (8)
Tell me about yourself and walk me through your background.Easy Why are you looking to leave your current role?Easy What are your greatest professional strengths and your biggest area for growth?Easy Where do you see yourself in three to five years?Easy What did you like most and least about your previous company or role?Medium Are you interviewing with other companies, and what is your current timeline?Medium What motivates you most in your day-to-day engineering work?Easy Can you describe a typical productive workday for you?Easy
Job Offer Negotiation (8)
How do you counter an initial job offer respectfully to negotiate a higher base salary?Medium How do you negotiate for more equity or stock options when base salary is fixed?Medium How do you negotiate a signing bonus to offset unvested stock or a missed annual bonus at your current job?Medium How do you handle an exploding job offer with a short 48-hour deadline?Medium How do you ask for more information about the company's equity grant (strike price, valuation, dilution)?Medium How do you handle a recruiter who asks for your current salary history during negotiations?Medium How do you negotiate an early performance or compensation review cycle into your offer?Medium What should you do after an employer accepts your negotiated counteroffer?Easy
Product Sense (6)
How would you design a notifications system for a ride-sharing mobile app?Medium If you noticed a 15% drop in daily active users (DAU) for our core web product, how would you investigate it?Hard How would you measure the success of a newly launched real-time collaboration feature?Medium How would you design a search and discovery experience for an online developer community?Medium How would you design an AI-powered code review feature in a pull request workflow?Hard How would you design an activity feed for a team collaboration platform?Medium
System Design (22)
Design a high-throughput URL shortening service (like bit.ly).Medium Design a scalable rate limiter for an API gateway.Medium Design a real-time collaborative document editing service.Hard Design a distributed caching architecture for a high-volume e-commerce platform.Hard Design a notification delivery service supporting email, SMS, and push notifications.Medium Design an image upload, processing, and delivery pipeline.Medium Design a web crawler that indexes billions of web pages.Hard Design a scalable video streaming platform (like YouTube).Hard Design a distributed logging and metrics monitoring platform (like Datadog).Hard Design an e-commerce flash sale system (handling massive concurrent inventory checkout).Hard Design a distributed job scheduler (like Cron or Celery).Hard Design a location-based nearby places service (like Yelp or Google Maps nearby search).Medium Design a real-time multiplayer leaderboard service for a gaming platform.Medium Design an auto-complete / search typeahead system.Medium Design a secure, scalable payment processing service.Hard Design a metrics aggregation and anomaly detection pipeline for IoT sensor data.Hard Design a webhooks delivery service (sending reliable event notifications to third-party developers).Medium Design a content recommendation feed (like Twitter or Instagram home feed).Hard Design a distributed session management system for a global enterprise SaaS application.Medium Design a high-volume email campaign sending platform (like Mailchimp).Hard What patterns do you use for resilient communication between microservices?Hard How would you implement distributed transactions across microservices (Saga pattern)?Hard
Technical (32)
What is Database Indexing, and how do B-Trees compare to Hash Indexes?Medium Explain the four ACID properties in relational databases and how isolation levels work.Hard What is Cross-Origin Resource Sharing (CORS), and how do preflight requests work?Medium Explain the differences between TCP and UDP, and when you would choose one over the other.Easy How does the HTTPS / TLS 1.3 handshake establish a secure connection?Hard What are microservices, and how do they compare to modular monoliths?Medium What is the difference between SQL and NoSQL databases, and when should you use each?Easy Explain Docker containers, images, and how containers differ from virtual machines.Easy What is Kubernetes, and what are its core architectural components?Medium What is CI/CD, and what are the essential stages of a modern production deployment pipeline?Easy Explain the CAP theorem and PACELC theorem in distributed systems.Hard Explain the differences between WebSockets, Server-Sent Events (SSE), and Long Polling.Medium How do you secure a REST API against common vulnerabilities (OWASP Top 10)?Hard What is GraphQL, and how does it compare to REST APIs? What is the N+1 problem in GraphQL?Medium How does Garbage Collection work in V8 (JavaScript) or modern runtimes?Hard Explain the differences between SQL Joins: INNER, LEFT, RIGHT, FULL OUTER, and CROSS joins.Easy What is Sharding in database systems, and how do Range-Based and Hash-Based sharding compare?Hard What is the difference between Synchronous and Asynchronous programming in backend systems?Easy What is Spring Boot, and how is it different from the Spring Framework?Easy How does Spring Boot auto-configuration work under the hood?Medium What is the difference between @Component, @Service, @Repository and @Controller in Spring?Easy Explain bean scopes in Spring and when you would use each one.Medium How do you handle exceptions globally in a Spring Boot REST API?Medium What is Spring Boot Actuator and which endpoints would you expose in production?Medium How do profiles and externalised configuration work in Spring Boot?Easy Explain how @Transactional works in Spring and its common pitfalls.Hard What is the N+1 query problem in Spring Data JPA, and how do you fix it?Medium How do you secure a Spring Boot REST API with JWT and Spring Security?Hard What is the difference between RestTemplate, WebClient and RestClient in Spring?Medium How do you test a Spring Boot application at different levels?Medium What are the advantages of constructor injection over field injection in Spring?Easy How would you improve the performance of a slow Spring Boot endpoint?Hard
Coding (16)
Given an array of integers `nums` and an integer `target`, return indices of the two numbers that add up to `target` (Two Sum).Easy Reverse a singly linked list in-place.Easy Given a string `s` containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid (Valid Parentheses).Easy Find the maximum subarray sum in an integer array `nums` (Kadane's Algorithm).Medium Given a collection of intervals, merge all overlapping intervals (Merge Intervals).Medium Determine if a linked list contains a cycle (Floyd's Tortoise and Hare Cycle Detection).Easy Given an array of strings `strs`, group the anagrams together (Group Anagrams).Medium Given an array of integers `height` representing an elevation map, compute how much water it can trap after raining (Trapping Rain Water).Hard Given a non-empty array of integers `nums`, every element appears twice except for one. Find that single one in linear runtime and constant space.Easy Given the root of a binary tree, invert the tree and return its root (Invert Binary Tree).Easy Find the longest substring without repeating characters in a given string `s`.Medium Given a 2D grid of '1's (land) and '0's (water), count the number of islands (Number of Islands).Medium Given an array of integers `nums` sorted in non-decreasing order, find the starting and ending position of a given `target` value in O(log N) time (Find First and Last Position).Medium You are given an integer array `coins` and an integer `amount`. Return the fewest number of coins needed to make up that amount, or -1 if impossible (Coin Change).Medium Serialize and deserialize a binary tree to and from a string.Hard Design a data structure that follows the constraints of a Least Recently Used (LRU) Cache.Hard

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