Article 07: API Gateway with Spring Cloud Gateway

1. Objective

Understand why an API Gateway is required and implement one using Spring Cloud Gateway.

2. Key Concepts

• API Gateway pattern
• Single entry point
• Routing
• Cross-cutting concerns

3. Problem Without API Gateway

Clients must:

• Call multiple services directly
• Handle different URLs
• Manage security individually

4. API Gateway Architecture

[Client]
   |
[API Gateway]
   |        |
[User]   [Order]
 Service  Service

5. Hands-On: Create API Gateway

Dependencies:

• spring-cloud-starter-gateway
• spring-cloud-starter-netflix-eureka-client

application.yml:

server:
  port: 8080

spring:
  application:
    name: api-gateway

6. Define Routes

spring:
  cloud:
    gateway:
      routes:
        - id: user-service
          uri: lb://USER-SERVICE
          predicates:
            - Path=/users/**
        - id: order-service
          uri: lb://ORDER-SERVICE
          predicates:
            - Path=/orders/**

7. Test Routing

• http://localhost:8080/users/1
• http://localhost:8080/orders/1

8. Common Mistakes

• Hardcoding service URLs
• Bypassing gateway
• Overloading gateway with business logic

9. Interview Notes

• Gateway handles cross-cutting concerns
• Improves security and maintainability

10. Summary

API Gateway centralizes routing and simplifies clients.

11. What’s Next

Implement filters and centralized configurations.