What can break in production, and how would I debug it?

Short explanation:

Production failures often come from conditions absent in small examples: parallel requests, large datasets, expired credentials or unavailable providers. A review should consider how the code exposes and recovers from these conditions. Observability is part of the design because a hidden failure is harder to correct safely.

Key points:

• Check scale, parallel requests, stale data and unavailable dependencies.

• Use request IDs, logs, metrics and traces to locate the failing step.

• Reproduce the failure and add a focused regression test.

• Check whether logs contain stable request or operation IDs and whether sensitive inputs are excluded.

Interview point:

• Explain how you would distinguish the suspected defect from other causes once the code is running.