Implementing API Idempotency in Distributed Node.js Systems

Use a unique 'Idempotency-Key' in headers, backed by a Redis-based TTL cache, to ensure a retry results in the same outcome without side effects.

In distributed systems, network failures lead to retries. If a 'Charge Credit Card' request is retried, the user shouldn't be charged twice. Senior architecture involves: 1. Client sends a unique Idempotency-Key. 2. Server checks Redis for the key. 3. If exists, return cached response. 4. If not, acquire a lock, process the request, store the result in Redis with a TTL, and release the lock. This protects against race conditions and duplicate processing.