I applied online. The process took 1 day.

The interview was quite challenging and heavily focused on practical, production-level backend concepts.

It started with React and Node.js fundamentals but quickly moved into in-depth discussions on Worker Threads, BullMQ, AWS SQS/Lambda, idempotency, distributed systems, PostgreSQL transactions, isolation levels, concurrency control, and query optimization.

The questions emphasized real-world implementation and design decisions rather than theoretical knowledge.

Overall, it felt closer to a strong SDE-2/SDE-3 level interview. As a fresher, it was quite difficult to keep up with the depth of the discussion, but it was a great learning experience.

How would you implement an idempotent consumer for an SQS + Lambda workflow and prevent duplicate processing under retries and at-least-once delivery?

How would you design an idempotent consumer in PostgreSQL so that processing the same message multiple times doesn't create duplicate rows or apply the same state change twice? Explain how you would use transactions, ON CONFLICT, unique constraints, and appropriate isolation levels to handle concurrency.