Stripe Backend Engineer Interview Questions

I would separate ingestion, durable storage, processing, and downstream fanout so each stage can scale independently. I would use queues or streams for buffering, checkpointing for recovery, and idempotent consumers so retries do not corrupt state. The design should favor durability and observability over raw throughput alone.

I would identify each step, make each one independently recoverable, and define compensation for steps that cannot be rolled back. In a payment flow, that might mean authorizing first, capturing later, and using reversal or refund paths when downstream steps fail. The goal is to leave the system in a reconcilable state after any interruption.

Synchronous processing gives immediate feedback, which is useful for user-facing actions that need a fast answer. Asynchronous processing improves resilience and throughput for work that can complete later, but it requires stronger reconciliation and clearer status visibility. In practice, I would keep the user-facing decision fast and move noncritical side effects to async paths.

I would use authentication, authorization, rate limiting, request validation, fraud signals, and anomaly detection. Payments are high-value targets, so the API needs layered defenses rather than a single gate. I would also log sensitive actions carefully so security monitoring and incident response are possible without exposing secrets.

I would optimize for correctness, immutability, and traceability before normalization convenience. That usually means explicit identifiers, timestamps, currency fields, versioning, and constraints that preserve invariants. A good schema should make the most dangerous mistakes hard to express.