How Do You Handle Failures?

Exactly-Once, Offsets, and Checkpoints Every streaming system will fail. The interviewer knows this. The question isn't whether failures happen - it's whether your pipeline produces correct results when they do. Your answer framework: start with delivery guarantees, then explain offset management, then describe your idempotency strategy. Hit all three and you've covered the full rubric. The interviewer wants to hear that at-least-once is the production default. Not exactly-once. The trap is answering "exactly-once" because it sounds correct. The real answer: at-least-once with idempotent sinks. If you process the same event twice, the result doesn't change. Upserts instead of inserts. Deduplication keys. This is what production systems actually use. Offset management is the follow-up trap.