Couchbase India Backend Engineer Interview: Rounds, Questions and Preparation

What the job involves

Backend engineers at global tech companies build and maintain the server-side systems that power applications, APIs, and data services. They write scalable, reliable code, design data models, and work with distributed systems to ensure performance and uptime. Day to day includes coding, code reviews, debugging, and collaborating with frontend, DevOps, and product teams.

Role and technical knowledge

1. 1

   Explain the difference between SQL and NoSQL databases, and when you would choose one over the other for a backend service.

   Cover data model, scalability, consistency, and use cases like transactional vs. flexible schema. Mention examples such as PostgreSQL vs. Couchbase.

2. 2

   What happens when you type a URL into a browser and hit enter, from a backend perspective?

   Walk through DNS resolution, TCP handshake, HTTP request, server processing, database queries, and response. Highlight caching and load balancing.

3. 3

   How would you design a REST API for a simple blog with users, posts, and comments?

   Define resources, endpoints, HTTP methods, status codes, and authentication. Discuss pagination and versioning.

4. 4

   What is the difference between a process and a thread? How does concurrency affect backend performance?

   Explain memory sharing, context switching, and race conditions. Mention how thread pools or async I/O improve throughput.

Practical scenarios

1. 5

   Your API is suddenly responding slowly. How do you debug and fix the issue?

   Outline monitoring, logging, profiling, checking database queries, and scaling options. Mention caching and query optimization.

2. 6

   You need to add a new feature that requires a database schema change without downtime. How do you approach it?

   Discuss backward-compatible migrations, feature flags, dual writes, and rollback plans. Emphasize testing in staging.

3. 7

   How would you handle a situation where two users try to book the last available item at the same time?

   Explain race conditions, transactions, locks, or optimistic concurrency. Mention idempotency and queue-based solutions.

4. 8

   You are asked to improve the performance of an existing query that takes several seconds. What steps do you take?

   Cover EXPLAIN plans, indexes, query rewriting, caching, and denormalization. Mention measuring before and after.

Behavioural and HR

1. 9

   Tell me about a time you worked in a team to complete a project. What was your role?

   Use STAR format. Highlight collaboration, communication, and how you handled disagreements or deadlines.

2. 10

   Describe a challenging technical problem you solved. How did you approach it?

   Show problem-solving steps, research, experimentation, and learning from failure. Emphasize persistence and outcome.

3. 11

   Why do you want to work as a backend engineer at a global tech company?

   Connect personal interest in scalable systems, data, and impact. Mention specific technologies or company values you admire.

4. 12

   Where do you see yourself in three years, and how does this role fit your goals?

   Show realistic growth plans like deepening technical expertise, leading small projects, or mentoring. Align with company's career path.

Coding and problem-solving

1. 13

   Given an array of integers, find two numbers that add up to a target sum. Discuss time and space complexity.

   Explain brute force vs. hash map approach. Code cleanly and analyze O(n) time and O(n) space.

2. 14

   How would you detect a cycle in a linked list? Implement and explain.

   Use Floyd's tortoise and hare algorithm. Discuss O(n) time and O(1) space, and edge cases.

3. 15

   Write a function to reverse a string in place. What are the trade-offs?

   Show two-pointer technique. Discuss immutable strings in languages like Java and memory considerations.

4. 16

   Design a simple LRU cache. What data structures would you use and why?

   Combine hash map and doubly linked list. Explain O(1) get and put, and eviction policy.