AWS Serverless Patterns and Anti-Patterns: What Works, What Breaks, and When to Use What

Serverless on AWS isn't "just use Lambda." It's a design philosophy: let AWS manage the infrastructure, pay only for what you use, and build with managed services that scale independently. But the patterns that work in serverless are fundamentally different from traditional architectures — and the anti-patterns are expensive to learn the hard way. This guide covers the patterns that work in production, the anti-patterns that waste money or cause outages, and the decision framework for when serverless is the right (or wrong) choice. The Serverless Building Blocks ┌─────────────────────────────────────────────────────────────────────┐ │ AWS SERVERLESS STACK │ ├─────────────────────────────────────────────────────────────────────┤ │ COMPUTE │ Lambda | Fargate (serverless containers) │ │ API │ API Gateway (REST/HTTP/WebSocket) | AppSync (GraphQL)│ │ ORCHESTRATION │ Step Functions | EventBridge Scheduler │ │ MESSAGING │ SQS | SNS | EventBridge │ │ STORAGE │ S3 | DynamoDB | Aurora Serverless │ │ STREAMING │ Kinesis | DynamoDB Streams | MSK Serverless │ │ AUTH │ Cognito | IAM | Lambda Authorizers │ │ OBSERVABILITY │ CloudWatch | X-Ray | Application Signals │ └─────────────────────────────────────────────────────────────────────┘ Key principle: In serverless, you compose applications from managed services. Lambda is the glue between them — not the application itself. Pattern 1: Synchronous API (Request/Response) The most common serverless pattern: HTTP API backed by Lambda. Client → API Gateway → Lambda → DynamoDB / Aurora Serverless │ Response ← ─ ─ ─ ─ ─ ─ ┘ Best Practices API Gateway HTTP API (not REST API) — cheaper, faster, simpler for most cases One Lambda per route (single responsibility) — not a monolith Lambda Keep Lambda warm — use Provisioned Concurrency for latency-sensitive endpoints DynamoDB for simple access patterns — scales with traffic, no connection pooling Aurora Serverless v2 for complex queries — but use RDS Proxy to manage connections When to Choose H