SDE2 Interview Questions at Razorpay

A Node.js microservice processes background jobs from a Redis queue. Under load, jobs fail and retry endlessly, creating a death loop that blocks the queue. How do you implement a proper retry strategy with dead letter handling?

Design Razorpay's payment retry system. When a payment fails due to a transient error (bank timeout, network blip), how do you retry safely without double-charging the customer? Cover: idempotency keys, exponential backoff with jitter, dead-letter queues, and reconciliation with bank statements.

You're building a feature flag system in React. Flags come from an API and affect which components render. How do you implement this so: flags load once at startup, components don't re-render when irrelevant flags change, and engineers can easily wrap any component.

Your JWT tokens are being stolen from localStorage and used in attacks. A developer suggests using httpOnly cookies instead. Describe the complete migration, including risks and security tradeoffs.

What is idempotency? Why is it critical for payment APIs and how do you implement it?

Design Razorpay's payout system (RazorpayX). Businesses send bulk payouts to thousands of vendor accounts simultaneously. Cover: batching, bank API rate limits, real-time status tracking, and failure handling.

Your Next.js app fetches user-specific data in getServerSideProps. The page load time is 3.2 seconds. CDN cache hit rate is 0%. Product team asks you to make it faster without losing personalization. What do you do?

How do you implement a distributed ledger for financial transactions? Explain double-entry bookkeeping in code, why you never update a balance directly, and how you use event sourcing to reconstruct the current balance from a transaction log.

Design Razorpay's dashboard for merchants. A merchant wants to see real-time revenue, transaction success rates, and refund trends. How do you aggregate millions of transactions into live charts with under 5-second latency?

Describe a production incident you were part of. Walk through the detection, triage, resolution, and post-mortem. What monitoring or process changes did you introduce afterwards?

Explain the difference between a payment gateway, payment processor, and acquiring bank. How does money actually move when a customer pays with a credit card on a Razorpay-powered checkout? Walk through each hop end to end.

Kafka guarantees message order within a partition but not across partitions. For a payments system, why does this matter, and how would you key messages to preserve per-account ordering?

Your service processes payments. During load testing at 5x normal traffic, you notice 0.01% of transactions are charged twice. At scale that's 1000 users per day. How do you find and fix this?

In PostgreSQL, what is the difference between SERIALIZABLE and READ COMMITTED isolation levels for a transaction that reads then updates an account balance?

Your REST API uses JWT. A user changes their password. How do you immediately invalidate their existing JWT tokens?