API Gateway Design Patterns

An API Gateway is the single entry point for all client requests into a microservices backend.

Core Responsibilities

• Request routing: Forward to correct microservice
• Authentication: Validate JWT/OAuth tokens
• Rate limiting: Protect services from abuse
• SSL termination: Handle HTTPS
• Request/Response transformation: Protocol translation
• Logging & Monitoring: Centralized observability

Architecture

Clients (Mobile, Web, 3rd Party)
          ↓
     API Gateway
     ↙  ↓  ↘
User  Order  Payment
Svc   Svc    Svc

Authentication Flow

1. Client sends request + JWT
2. Gateway validates JWT with Auth Service
3. On success, forward to backend
4. Return response to client

BFF Pattern (Backend for Frontend)

Create separate gateways per client type:

• Mobile BFF: Returns compressed, minimal data
• Web BFF: Returns full rich data
• Partner BFF: Strict rate limits, audit logs

Popular Tools

Tool	Use Case
Kong	Open-source, plugin-rich
AWS API Gateway	Serverless, managed
Nginx	High performance proxy
Envoy	Service mesh sidecar

Anti-Patterns

• Don't put business logic in the gateway
• Avoid gateway as a bottleneck — scale horizontally

Conclusion

API Gateways centralize cross-cutting concerns, simplify client interactions, and secure microservices backends.