API Gateway Architecture: Routing, Auth & Rate Limiting

An API Gateway is the single entry point and architectural front door for all client traffic into an enterprise microservice ecosystem (e.g. Kong, Traefik, Envoy, AWS API Gateway).

By centralizing cross-cutting operational concerns—Routing, SSL Termination, Authentication Verification, Rate Limiting, and Telemetry Logging—individual backend microservices remain lightweight, focused purely on business domain logic.

┌─────────────────────────────────────────────────────────────┐
│                 API Gateway Centralized Capabilities         │
│                                                             │
│  Incoming Client Requests (HTTPS)                           │
│             │                                               │
│             ▼                                               │
│  ┌───────────────────────────────────────────────────────┐  │
│  │                     API GATEWAY                       │  │
│  │ 1. SSL/TLS Termination (Manages Certs)                │  │
│  │ 2. JWT Verification (Rejects invalid tokens)          │  │
│  │ 3. Rate Limiting (Protects downstream services)       │  │
│  │ 4. Request Routing & Header Transformation            │  │
│  └───────────────────────────────────────────────────────┘  │
│             │                  │                 │          │
│             ▼                  ▼                 ▼          │
│       [Auth Service]    [Orders Service]   [Catalog Service]│
└─────────────────────────────────────────────────────────────┘

1. Key Responsibilities of an API Gateway

SSL/TLS Termination: Manages TLS certificates and decrypts HTTPS traffic at the perimeter.
Authentication Offloading: Verifies incoming JWT signatures once at the gateway; passes sanitized user claims (X-User-Id: 42) to internal services.
Dynamic Routing: Directs /api/v1/orders to the orders cluster and /api/v1/users to the users cluster.
Protocol Translation: Translates external HTTP/JSON requests into internal high-speed gRPC calls.

Summary & Key Takeaways

API Gateways act as the unified security and routing perimeter for microservices.
Centralizes TLS termination, JWT validation, rate limiting, and access logging.
Decouples client interfaces from internal microservice network topology.

Best Practices & Senior Guidance

Never Put Heavy Business Logic in the Gateway: Keep gateways fast and non-blocking; route domain computation to microservices.