API Gateway in microservices architecture

 

🔍 What is an API Gateway?

An API Gateway is a server that acts as a single entry point into a system, typically for microservices architecture.

It handles requests by:

• Routing them to the appropriate microservice

• Applying security, rate limiting, authentication

• Performing load balancing, logging, caching, etc.

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📦 Why Use an API Gateway?

Feature	Purpose
🔁 Request Routing	Directs incoming requests to appropriate backend services
🔐 Security	Centralized authentication and authorization
⚖️ Load Balancing	Distributes traffic among service instances
🔄 Protocol Translation	Translates protocols (HTTP to WebSocket, etc.)
📉 Rate Limiting	Prevents abuse by limiting requests per client
📄 Aggregation	Combines responses from multiple services into one
📊 Monitoring	Tracks usage, logs, and metrics
🌍 CORS Handling	Cross-origin resource sharing setup

🧱 Architecture Diagram:

less
     [Client App]
          |
          v
    [API Gateway] ---> [User Service]
          |            [Order Service]
          |            [Product Service]
          v
     [Auth Service]

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🚀 Common API Gateway Tools

Tool	Language	Notes
🔹 Spring Cloud Gateway	Java (Spring Boot)	Official Spring API Gateway
🔹 Zuul (Netflix)	Java	Older Netflix API Gateway (no longer maintained)
🔹 NGINX	C	Lightweight, powerful reverse proxy
🔹 Kong	Lua	Enterprise-grade open source API Gateway
🔹 Amazon API Gateway	Cloud	Managed gateway on AWS

🛠️ Example: Spring Cloud Gateway (Java)

1️⃣ Dependency (Maven):

xml
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-gateway</artifactId>
</dependency>

2️⃣ application.yml config:

yaml
spring:
  cloud:
    gateway:
      routes:
        - id: user-service
          uri: http://localhost:8081
          predicates:
            - Path=/users/**
        - id: order-service
          uri: http://localhost:8082
          predicates:
            - Path=/orders/**

3️⃣ Main class:

java
@SpringBootApplication
public class ApiGatewayApplication {
    public static void main(String[] args) {
        SpringApplication.run(ApiGatewayApplication.class, args);
    }
}

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🔐 API Gateway with Security (JWT)

• Intercepts incoming requests

• Validates JWT token

• Rejects unauthorized users before hitting backend microservices

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📊 Advanced Features

• Rate limiting (RequestRateLimiter)

• Circuit breaker (resilience4j, Hystrix)

• Path rewriting

• Load balancing with service discovery (Eureka)

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📌 Pros and Cons

✅ Advantages:

• Centralized control

• Simplified client code

• Unified security

❌ Disadvantages:

• Single point of failure (unless highly available)

• Can become bottleneck if not scaled properly

• Adds complexity