Architectural Design Patterns in Modern Cloud Infrastructure

Writing code that works under ideal conditions is straightforward. Engineering systems that degrade gracefully during network partitions, upstream API outages, and sudden traffic spikes requires deliberate architectural patterns.

### Key Resilience Patterns

1. **Idempotency Keys in Mutation APIs**: Every POST/PATCH transaction accepts an Idempotency-Key header. Distributed workers check Redis locks before executing side effects (such as charges or webhook dispatches), ensuring network retries never produce duplicate states.
2. **Circuit Breakers for External Dependencies**: When downstream third-party APIs start returning server-side errors, the circuit breaker trips open, serving cached fallbacks or queuing requests without blocking incoming HTTP threads.
3. **Token-Bucket Rate Limiting**: Enforcing rate limits at the API gateway layer protects internal databases from query floods during automated scraping bursts.

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