As microservices architectures grow, the need for a centralized entry point becomes vital. This is where API Gateways come in. In the Spring ecosystem, Spring Cloud Gateway offers a powerful, lightweight, and flexible solution for this purpose.
In this guide, we’ll dive deep into configuring Spring Cloud Gateway for microservices, covering route definitions, filters, load balancing, and service discovery with Eureka.
📦 Project Structure
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com.kscodes.springboot.microservice ├── gateway-service ├── service-a └── service-b |
All services are registered to Eureka, and the Gateway will route the incoming requests to the appropriate microservices.
🧰 Step 1: Add Dependencies
🧩 pom.xml for Gateway
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<dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-gateway</artifactId> </dependency> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId> </dependency> </dependencies> |
In your parent section:
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<dependencyManagement> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-dependencies</artifactId> <version>2023.0.0</version> <type>pom</type> <scope>import</scope> </dependency> </dependencies> </dependencyManagement> |
⚙️ Step 2: application.yml for Gateway
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server: port: 8080 spring: application: name: gateway-service cloud: gateway: discovery: locator: enabled: true lower-case-service-id: true routes: - id: service-a uri: lb://service-a predicates: - Path=/api/service-a/** filters: - RewritePath=/api/service-a/(?<segment>.*), /${segment} - id: service-b uri: lb://service-b predicates: - Path=/api/service-b/** filters: - RewritePath=/api/service-b/(?<segment>.*), /${segment} eureka: client: service-url: defaultZone: http://localhost:8761/eureka |
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lb://means it’s using Ribbon/LoadBalancer with Eureka for service lookup.
🚀 Step 3: Basic Microservice Setup
✅ service-a Example Controller
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package com.kscodes.springboot.microservice.servicea; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RestController; @RestController public class ServiceAController { @GetMapping("/hello") public String sayHello() { return "Hello from Service A!"; } } |
Ensure that application.yml has:
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spring: application: name: service-a server: port: 8081 eureka: client: service-url: defaultZone: http://localhost:8761/eureka |
Do the same for service-b on port 8082.
🔒 Step 4: Add Custom Filters (Optional)
You can define a custom filter to log requests or validate headers.
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package com.kscodes.springboot.microservice.gatewayservice; import org.springframework.cloud.gateway.filter.GatewayFilter; import org.springframework.cloud.gateway.filter.GatewayFilterChain; import org.springframework.stereotype.Component; import org.springframework.web.server.ServerWebExchange; import reactor.core.publisher.Mono; @Component public class LoggingFilter implements GatewayFilter { @Override public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) { System.out.println("Incoming request to URI: " + exchange.getRequest().getURI()); return chain.filter(exchange); } } |
Add this filter to your route via Java configuration if needed.
🌐 Step 5: Test Your Setup
Start Eureka, both services, and the Gateway.
Test with:
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http://localhost:8080/api/service-a/hello http://localhost:8080/api/service-b/hello |
✅ Gateway routes requests to appropriate services using path predicates and rewrites.
📈 Benefits of Spring Cloud Gateway
- ✅ Native Spring Boot integration
- 🔄 Dynamic routing with Eureka
- 🧱 Supports filters and predicates
- 🔐 Works well with OAuth2, security filters
- ⚡ Light footprint and non-blocking (Reactor-based)
🏁 Conclusion
Using Spring Cloud Gateway for Microservices gives your architecture a scalable and centralized API layer. With built-in integration for Eureka, filters, and path routing, it becomes the perfect entry point for modern cloud-native applications.