AdvancedTechnical
5 min
Designing Idempotent APIs
APIIdempotencyReliability
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Interview Question
What does idempotency mean in APIs, and how would you design idempotent operations in REST or gRPC services?
Key Points to Cover
- Explain idempotency in HTTP methods (GET, PUT, DELETE vs POST)
- Use idempotency keys for POST operations
- Ensure backend deduplication and retry handling
- Log and monitor idempotent request outcomes
Evaluation Rubric
Defines idempotency correctly30% weight
Designs idempotent operations in APIs30% weight
Uses idempotency keys effectively20% weight
Ensures retries don’t cause duplication20% weight
Hints
- 💡Think payment APIs as a key use case.
Common Pitfalls to Avoid
- ⚠️Assuming all HTTP methods are idempotent by default without understanding their semantics.
- ⚠️Not clearly defining or documenting the expected idempotency behavior for specific endpoints or services.
- ⚠️Implementing idempotency without a robust backend mechanism to store and retrieve request outcomes, leading to race conditions or incorrect deduplication.
- ⚠️Failing to handle the storage and eventual cleanup of idempotency keys, which can lead to unbounded growth of the storage.
- ⚠️Not considering idempotency for network-level retries by clients, leaving the system vulnerable to duplicate operations.
Potential Follow-up Questions
- ❓How do you store idempotency keys?
- ❓What about expiration of keys?
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