API Gateway Pattern - Cloud Patterns

Definition

The API Gateway Pattern provides a single entry point for all clients to access backend services. It acts as a reverse proxy, routing requests to appropriate microservices, aggregating results, and handling cross-cutting concerns like authentication, rate limiting, and logging.

When to Use It

Building microservices architecture
You need a single entry point for clients
Handling cross-cutting concerns centrally
Different client types require different APIs
Request/response transformation needed
Implementing API versioning and routing

Pros & Cons

✓ Pros

Single entry point simplifies client code
Centralized cross-cutting concerns
Protocol translation (REST to gRPC)
Request aggregation from multiple services
Better security and access control
Rate limiting and throttling

✗ Cons

Single point of failure
Potential performance bottleneck
Additional network hop
Increased latency
Gateway can become complex
Requires high availability setup

Architecture Diagram

┌─────────────────────────────────────────────────────────┐
│                        Clients                          │
│  ┌──────────┐   ┌──────────┐   ┌──────────┐           │
│  │   Web    │   │  Mobile  │   │   IoT    │           │
│  │  Browser │   │   App    │   │  Device  │           │
│  └────┬─────┘   └────┬─────┘   └────┬─────┘           │
└───────┼──────────────┼──────────────┼──────────────────┘
        │              │              │
        └──────────────┴──────────────┘
                       │
                       ▼
        ┌──────────────────────────────┐
        │       API Gateway            │
        │                              │
        │  • Authentication            │
        │  • Rate Limiting             │
        │  • Request Routing           │
        │  • Load Balancing            │
        │  • Response Aggregation      │
        │  • Caching                   │
        │  • SSL Termination           │
        │  • Request/Response Transform│
        └──────────────┬───────────────┘
                       │
        ┌──────────────┼───────────────┐
        │              │               │
        ▼              ▼               ▼
  ┌──────────┐  ┌──────────┐  ┌──────────┐
  │  User    │  │ Product  │  │ Order    │
  │ Service  │  │ Service  │  │ Service  │
  │          │  │          │  │          │
  │ REST API │  │ gRPC API │  │ GraphQL  │
  └────┬─────┘  └────┬─────┘  └────┬─────┘
       │             │             │
       ▼             ▼             ▼
  ┌─────────┐  ┌─────────┐  ┌─────────┐
  │  User   │  │ Product │  │  Order  │
  │   DB    │  │   DB    │  │   DB    │
  └─────────┘  └─────────┘  └─────────┘

Request Flow Example:
─────────────────────

1. Client → Gateway: GET /api/user/123/orders
2. Gateway authenticates request
3. Gateway checks rate limits
4. Gateway routes to:
   • User Service: GET /users/123
   • Order Service: GET /orders?userId=123
5. Gateway aggregates responses
6. Gateway returns combined result to client

Features:
• Single endpoint for clients
• Protocol translation
• Request aggregation
• Cross-cutting concerns handled centrally