Amazon API Gateway

Amazon API Gateway is a managed service for creating, publishing, and operating HTTP, REST, and WebSocket APIs at scale. It fronts backend services (Lambda, containers, EC2, public HTTP endpoints) with authentication, request validation, rate limiting, and caching — the standard AWS entry point for serverless and microservice APIs.

API Types:

• HTTP APIs: Newer, lower-cost, lower-latency — ~70% cheaper than REST APIs. Supports JWT authorizers, CORS, auto-deploy. Best default for new APIs.
• REST APIs: Feature-complete classic option — request validation, API keys & usage plans, AWS WAF, private endpoints, caching, canary releases. Use when you need these features.
• WebSocket APIs: Bidirectional, long-lived connections — chat, notifications, live updates.

Key Features:

• Authorization: IAM, Cognito User Pools, JWT (HTTP APIs), and Lambda authorizers for arbitrary logic.
• Request/Response Transformation: Map between client and backend contracts without changing either.
• Throttling & Quotas: Per-stage, per-method, and per-API-key rate limits; burst and steady-state controls.
• Caching (REST): In-gateway response cache (0.5–237 GB) with per-method TTL.
• Stages & Canary Deployments: Percentage-based traffic shifting for blue/green rollouts.
• Private APIs: Accessible only from your VPC via interface endpoints.
• Observability: CloudWatch metrics, access logs, X-Ray tracing, execution logs.

Common Architectures:

• Serverless REST API: API Gateway → Lambda → DynamoDB, with Cognito-auth'd clients.
• Public Entry to Private ALB: API Gateway with a VPC Link forwarding to an internal Application Load Balancer fronting ECS/EKS services.
• Multi-Tenant SaaS: API keys + usage plans for per-tenant rate limiting and metering.
• Real-Time: WebSocket API → Lambda → DynamoDB connections table for push notifications.

API Gateway vs. Alternatives:

• Application Load Balancer (ALB): Cheaper and lower-latency for container backends, but lacks first-class auth, request validation, throttling, and API keys.
• AWS AppSync: Managed GraphQL — choose over API Gateway when your clients need GraphQL subscriptions or a unified schema.
• CloudFront Functions / Lambda@Edge: Edge-runtime request manipulation; pair with API Gateway for global low-latency delivery.