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Duplicate payments are a nightmare. Users get charged twice. This happens during network failures. You need idempotent APIs.
An idempotent API is simple. Sending the same request ten times gives the same result as sending it once. This is vital for payments and resource updates.
Use an idempotency key. The client sends a unique key in the header. The server checks this key. If the server saw it before, it sends the old response. It does not run the operation again.
Store keys in a database. Use a unique constraint. Set a time limit. A 24 hour window works for most retries.
Follow these rules:
- GET, PUT, and DELETE are idempotent by default.
- POST needs a key.
- Prefer PUT for updates.
Test your system. Simulate network failures and duplicate requests. These tests find race conditions.
Stop over-engineering. Build for the problems you have today. Use boring technology. Focus on observability. You need logs, metrics, and tracing.
Audit your backend this week. Check your error handling. Implement one new pattern this month.
Source: https://dev.to/therizwansaleem/designing-idempotent-apis-why-it-matters-and-how-to-do-it-right-4lh