serverless

Serverless Patterns

Function Design

• Single responsibility — one function, one purpose
• Stateless — no local state between invocations
• Idempotent — safe to retry without side effects
• Keep cold start time minimal (<500ms target)
• Set appropriate memory and timeout limits

Cold Start Optimization

• Minimize dependency bundle size
• Use tree-shaking and dead code elimination
• Initialize SDK clients outside the handler
• Use provisioned concurrency for latency-sensitive functions
• Prefer lightweight runtimes (Node.js, Python, Go)

// Initialize OUTSIDE handler (reused across invocations)
const dbClient = new DatabaseClient();
const cacheClient = new CacheClient();

// Handler function
export async function handler(event: Event): Promise<Response> {
  // Use pre-initialized clients
  const result = await dbClient.query(event.input);
  return formatResponse(result);
}

Event-Driven Architecture

• Use message queues for async processing
• Implement dead letter queues for failed messages
• Use event schemas for type safety
• Implement circuit breakers for external service calls
• Design for at-least-once delivery — make handlers idempotent

Timeouts & Retries

• API Gateway timeout: 29s max
• Lambda/Function timeout: match workload (default 30s)
• Use exponential backoff with jitter for retries
• Set max retry count (typically 3)
• Dead letter queue for exhausted retries

Observability

• Structured JSON logging with correlationId
• Custom metrics for business KPIs
• Distributed tracing across functions
• Alert on: error rate, duration p99, throttles, DLQ depth