Design Patterns & Failure Handling

Most system design interviews are evaluating your handling of partial failure.

Core patterns

• Caching (read-through, write-through, write-back)
• Queues and async workers
• Idempotency keys
• Rate limiting
• Circuit breakers and bulkheads
• Backpressure

Failure handling checklist

• Timeouts set everywhere (and sane)
• Retries capped + backoff + jitter
• Fallbacks for degraded dependencies
• Dead-letter queues for async
• Rollback plan

Observability checklist

• SLIs: latency, errors, saturation
• dashboards show p95/p99
• alerts are actionable
• tracing for dependency chains