Groww Backend Engineer Interview: Rounds, Questions and Preparation

What the job involves

Backend engineers at Indian unicorns and high-growth startups like Groww build and maintain the server-side systems that power consumer-facing apps, internal tools, and data pipelines. They write APIs, design database schemas, optimise performance, and ensure high availability for millions of users. The role involves close collaboration with frontend, product, and DevOps teams in fast-paced, iterative environments.

Role and Technical Knowledge

1. 1

   Explain how you would design a REST API for a stock trading app that handles thousands of requests per second.

   Cover endpoint design, rate limiting, caching, database sharding, and load balancing. Mention idempotency and authentication.

2. 2

   What is the difference between SQL and NoSQL databases? When would you choose one over the other for a fintech application?

   Discuss ACID compliance, scalability, schema flexibility, and use cases like transactions vs. user profiles. Give examples like PostgreSQL vs. MongoDB.

3. 3

   How does a load balancer work, and what are the common algorithms used?

   Explain round-robin, least connections, and IP hash. Mention health checks and session persistence.

4. 4

   Describe how you would handle database migrations in a live production environment with zero downtime.

   Talk about backward-compatible changes, blue-green deployments, and using tools like Flyway or Liquibase.

Practical Scenarios

1. 5

   Your API is experiencing high latency during peak hours. How would you diagnose and fix the issue?

   Mention monitoring tools (e.g., Prometheus, Grafana), checking database slow queries, adding caching, and scaling horizontally.

2. 6

   You need to implement a feature that sends real-time notifications to users. What technologies and design would you use?

   Discuss WebSockets, message queues (e.g., RabbitMQ, Kafka), and push notification services. Consider scalability and reliability.

3. 7

   How would you secure a backend service that handles sensitive user data like PAN and Aadhaar numbers?

   Cover encryption at rest and in transit, tokenization, access controls, and compliance with regulations like RBI guidelines.

4. 8

   You are asked to reduce the cost of your cloud infrastructure without affecting performance. What steps would you take?

   Suggest rightsizing instances, using spot instances, optimizing storage, and leveraging auto-scaling.

Problem Solving and Coding

1. 9

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

   Use a hash map for O(n) time. Explain trade-offs with sorting approach.

2. 10

   Write a function to detect a cycle in a linked list. How would you modify it to find the starting node of the cycle?

   Floyd's cycle-finding algorithm. Explain slow and fast pointers and mathematical proof.

3. 11

   Design a rate limiter for an API. What data structures would you use?

   Discuss token bucket, leaky bucket, or sliding window. Mention Redis for distributed rate limiting.

4. 12

   How would you find the top K frequent elements in a large stream of data?

   Use a min-heap of size K or count-min sketch for approximate counts. Discuss memory constraints.

Behavioural and HR

1. 13

   Tell me about a time you had to learn a new technology quickly for a project. How did you approach it?

   Use STAR method. Highlight self-learning, resources used, and successful outcome.

2. 14

   Describe a situation where you disagreed with a teammate's technical decision. How did you handle it?

   Show respect, data-driven discussion, and willingness to compromise for the team's goal.

3. 15

   Why do you want to work at a high-growth startup like Groww rather than a large MNC?

   Express interest in ownership, fast-paced learning, and impact. Avoid criticising MNCs.

4. 16

   Where do you see yourself in three years in terms of technical and career growth?

   Align with the company's growth, mention deepening backend expertise and taking on leadership roles.