In any retry-prone system — payment gateways, provisioning services, async job queues — idempotency is your safety net.
Patterns:
- Client-generated UUIDs
- Idempotency keys with deduplication storage
- Replay protection using Redis or database constraints
Example: Stripe’s use of Idempotency-Key header is a textbook implementation.
Make sure your side effects are idempotent or cancel-safe.