Pattern 23 / RESILIENCE

Idempotency

Use this when making retries safe when clients cannot know if a write succeeded.

Pressure: Making retries safe when clients cannot know if a write succeeded
Mechanism: Deduplicate requests with an idempotency key or natural operation identity
Toll: Requires storing keys/results and checking duplicates on the write path

Diagram for Idempotency — Architecture plate23

Executive brief

Idempotency fits when making retries safe when clients cannot know if a write succeeded. Mechanism: deduplicate requests with an idempotency key or natural operation identity. Use it for payments, order creation, message handling, and any retried write API. The toll: requires storing keys/results and checking duplicates on the write path.

Use when

Payments, order creation, message handling, and any retried write api.

Example

Same payment key returns original charge instead of charging twice.

Review framing

Describe the pressure first, then the mechanism, then the cost. That keeps the design grounded.

Same pressure family

Reliability Patterns

19Circuit Breaker 20Retry with Exponential Backoff 21Bulkhead 22Timeout 24Dead Letter Queue (DLQ)25Graceful Degradation