What is the API Gateway Pattern and what are its advantages?

What is an API Gateway?

An API Gateway is a single entry point for all client requests in a microservices architecture.

Instead of clients calling multiple microservices directly, they call the API Gateway, which then routes the request to the appropriate backend service.

🔹 Why Do We Need an API Gateway?

Without an API Gateway:

  • Clients must know the location of every microservice

  • Security, logging, and validation logic gets duplicated

  • Changes in backend services affect clients

👉 API Gateway solves all of this.

🔹 Core Responsibilities of an API Gateway

  1. Request Routing

    • Routes requests to correct microservice

    • /orders → Order Service

  2. Authentication & Authorization

    • JWT validation

    • OAuth2 handling

    • Role-based access control

  3. Rate Limiting

    • Prevents abuse (e.g., 100 req/min per user)

  4. Load Balancing

    • Distributes traffic among service instances

  5. Request/Response Transformation

    • Modify headers or payloads

  6. Centralized Logging & Monitoring

  7. Circuit Breaking & Resilience

    • Prevents cascading failures

🔹 Popular API Gateways

  • Spring Cloud Gateway

  • Netflix Zuul (older)

  • Kong

  • NGINX

  • AWS API Gateway

🔹 Example Architecture

Client
⬇
API Gateway
⬇
Order Service
Payment Service
User Service

🔹 Example (Spring Cloud Gateway Route)

spring:
cloud:
gateway:
routes:
- id: order-service
uri: http://localhost:8081
predicates:
- Path=/orders/**

🔹 Advantages of API Gateway

✅ Centralized security
✅ Simplifies client-side logic
✅ Improves performance
✅ Enables microservice scalability
✅ Hides internal service structure

🔹 Drawbacks

❌ Single point of failure (if not HA)
❌ Can become performance bottleneck
❌ Adds operational complexity

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