building-api-gateway

# Building API Gateway ## Overview Create an API gateway that provides unified entry point routing, load balancing, authentication enforcement, rate limiting, request transformation, and response aggregation across multiple backend microservices. Support path-based and header-based routing, circuit breaker protection for downstream services, and centralized cross-cutting concern management. ## Prerequisites - Multiple backend API services with known endpoints, health check URLs, and authentication requirements - Gateway framework: Express Gateway, Kong (declarative config), KrakenD, or custom Node.js/Go implementation - Service registry or static upstream configuration for backend service discovery - TLS certificates for gateway termination and optional mTLS for backend communication - Centralized logging and metrics collection for gateway-level observability ## Instructions 1. Inventory all backend services using Read and Grep, documenting their base URLs, endpoint paths, authentication requirements, and health check endpoints. 2. Define routing rules that map public-facing URL patterns to backend service endpoints: path-based (`/users/*` -> user-service), header-based (`X-API-Version: 2` -> v2-service), or method-based routing. 3. Implement authentication at the gateway layer: validate JWT tokens, API keys, or OAuth2 tokens once at the gateway and forward authenticated user context to backend services via headers (`X-User-ID`, `X-User-Roles`). 4. Add rate limiting at ...