Upgrade Your Microservice Gateway: Auto‑Routing and Load Balancing with Spring Cloud Gateway + Nacos

Background

In a previous article we covered the basic usage of Spring Cloud Gateway. This continuation explores advanced features such as integrating a service registry for automatic request forwarding and a configuration center for dynamic route loading.

Integrating the Service Registry

Spring Cloud Gateway can automatically proxy all services registered in a service registry. By registering the gateway itself with the registry, it creates dynamic routes using the service name as the target URI.

Example workflow diagram (omitted).

2.1 Build the Gateway Service

Copy an existing gateway-server project to a new module named gateway-nacos and add the Nacos discovery dependency in pom.xml:

<properties>
  <maven.compiler.source>8</maven.compiler.source>
  <maven.compiler.target>8</maven.compiler.target>
  <spring-boot.version>2.2.5.RELEASE</spring-boot.version>
  <spring-cloud.version>Hoxton.SR3</spring-cloud.version>
  <spring-cloud-alibaba.version>2.2.3.RELEASE</spring-cloud-alibaba.version>
</properties>

<dependencies>
  <!-- Spring Cloud Gateway component -->
  <dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-gateway</artifactId>
  </dependency>
  <!-- Nacos discovery -->
  <dependency>
    <groupId>com.alibaba.cloud</groupId>
    <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
  </dependency>
</dependencies>

<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-dependencies</artifactId>
      <version>${spring-boot.version}</version>
      <type>pom</type>
      <scope>import</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework.cloud</groupId>
      <artifactId>spring-cloud-dependencies</artifactId>
      <version>${spring-cloud.version}</version>
      <type>pom</type>
      <scope>import</scope>
    </dependency>
    <dependency>
      <groupId>com.alibaba.cloud</groupId>
      <artifactId>spring-cloud-alibaba-dependencies</artifactId>
      <version>${spring-cloud-alibaba.version}</version>
      <type>pom</type>
      <scope>import</scope>
    </dependency>
  </dependencies>
</dependencyManagement>

2.2 Modify Configuration Files

Update application.yaml to enable the discovery locator and point to the Nacos server:

server:
  port: 8080

spring:
  application:
    name: gateway-nacos
  cloud:
    gateway:
      # GatewayProperties
    discovery:
      locator:
        enabled: true
        url-expression: "'lb://' + serviceId"
    nacos:
      discovery:
        server-addr: 127.0.0.1:8848

nacos.discovery.server-addr

: Nacos as the Spring Cloud service registry. gateway.discovery.locator.enabled: Turn on integration with the service registry (default false). gateway.discovery.locator.url-expression: Spring EL expression that builds the target URI, default 'lb://' + serviceId.

Example of url-expression with services user-service and order-service:

spring:
  cloud:
    gateway:
      routes:
        - id: ReactiveCompositeDiscoveryClient_user-service
          uri: lb://user-service
          predicates:
            - Path=/user-service/**
          filters:
            - RewritePath=/user-service/(?<remaining>.*),/${remaining}
        - id: ReactiveCompositeDiscoveryClient_order-service
          uri: lb://order-service
          predicates:
            - Path=/order-service/**
          filters:
            - RewritePath=/order-service/(?<remaining>.*),/${remaining}

The lb:// prefix indicates load‑balanced forwarding to the target service instance.

2.3 Build a Business Microservice

Create a simple Spring Boot service named user-service and add the same Nacos discovery dependency:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
  <groupId>com.alibaba.cloud</groupId>
  <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
</dependency>

Enable discovery with @EnableDiscoveryClient and expose a test endpoint:

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

@RestController
public class HelloController {
    @GetMapping("/hello")
    public String hello() {
        return "hello，我是用户服务";
    }
}

Configure the service port and Nacos address in application.properties:

spring.application.name=user-service
server.port=9010
spring.cloud.nacos.discovery.server-addr=127.0.0.1:8848

2.4 Service Test

Start both the gateway and user-service. Access the Nacos console to verify registration. The gateway automatically proxies requests using the pattern http://gateway-host:port/{serviceId}/path. For example, http://127.0.0.1:8080/user-service/hello forwards to the

user-service

/hello

endpoint.

When a service runs on multiple instances, the gateway performs round‑robin load balancing.

Integrating the Configuration Center

Sometimes different services require distinct routing rules or filters, and we may not want to expose every service through the gateway. By moving route definitions to a configuration center (Nacos), the gateway can load them dynamically.

3.1 Build a New Gateway Project

Copy the previous gateway-nacos project to gateway-application and add the Nacos config dependency:

<dependencies>
  <dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-gateway</artifactId>
  </dependency>
  <dependency>
    <groupId>com.alibaba.cloud</groupId>
    <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
  </dependency>
  <dependency>
    <groupId>com.alibaba.cloud</groupId>
    <artifactId>spring-cloud-starter-alibaba-nacos-config</artifactId>
  </dependency>
</dependencies>

3.2 Modify Configuration Files

Nacos configuration items are only effective in bootstrap.yaml. Rename application.yaml to bootstrap.yaml and add the following:

server:
  port: 8080

spring:
  application:
    name: gateway-application
  cloud:
    nacos:
      discovery:
        server-addr: 127.0.0.1:8848
      config:
        server-addr: 127.0.0.1:8848
        namespace: 
        group: DEFAULT_GROUP
        name: gateway-config
        file-extension: yaml

This defines a dataId gateway-config in the DEFAULT_GROUP namespace.

3.3 Publish Route Configuration to Nacos

In the Nacos console, create a configuration with dataId gateway-config and content:

spring:
  cloud:
    gateway:
      routes:
        - id: user-service
          uri: lb://user-service
          predicates:
            - Path=/user-service/**
          filters:
            - RewritePath=/user-service/(?<remaining>.*),/${remaining}

When the gateway starts, it automatically loads these routes and refreshes them on change.

3.4 Service Test

After restarting the gateway, accessing http://127.0.0.1:8080/user-service/hello returns the same response as before, confirming dynamic loading.

Modify the route in Nacos to change the path from /user-service to /user. After publishing, the request http://127.0.0.1:8080/user/hello succeeds, demonstrating that the gateway refreshed the rule without a restart.

Conclusion

Spring Cloud Gateway is a powerful gateway component. In microservice architectures it is typically paired with a service registry and a configuration center (such as Nacos) to achieve unified request forwarding, dynamic route management, and load balancing.

References

1. https://www.iocoder.cn/Spring-Cloud/Spring-Cloud-Gateway/?self