How to Consume Services with Spring Cloud’s LoadBalancerClient

Overview

The article demonstrates how to use Spring Cloud's LoadBalancerClient to consume a service registered in Eureka (or Consul). It builds a consumer project, adds required dependencies, configures the application, and implements a REST controller that selects a service instance via load balancing and invokes its endpoint.

1. Create the Consumer Project

Generate a new Maven project named eureka-consumer and add the following dependencies to pom.xml (parent and dependencyManagement sections omitted for brevity):

<dependencies>
  <dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-eureka</artifactId>
  </dependency>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
  </dependency>
</dependencies>

2. Application Configuration

In src/main/resources/application.properties specify the consumer’s name, port, and the Eureka server address:

spring.application.name=eureka-consumer
server.port=2101
eureka.client.serviceUrl.defaultZone=http://localhost:1001/eureka/

3. Main Application Class

Enable discovery and expose a RestTemplate bean:

@EnableDiscoveryClient
@SpringBootApplication
public class Application {
    @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
    public static void main(String[] args) {
        new SpringApplicationBuilder(Application.class).web(true).run(args);
    }
}

4. Consumer Controller

Create a REST controller that injects LoadBalancerClient and RestTemplate. The /consumer endpoint selects an instance of the provider service ( eureka-client), builds the target URL, and forwards the request:

@RestController
public class DcController {
    @Autowired
    LoadBalancerClient loadBalancerClient;
    @Autowired
    RestTemplate restTemplate;

    @GetMapping("/consumer")
    public String dc() {
        ServiceInstance instance = loadBalancerClient.choose("eureka-client");
        String url = "http://" + instance.getHost() + ":" + instance.getPort() + "/dc";
        System.out.println(url);
        return restTemplate.getForObject(url, String.class);
    }
}

5. How It Works

The LoadBalancerClient.choose() method queries the Eureka registry, applies a load‑balancing algorithm, and returns a ServiceInstance containing host and port information. The consumer then constructs the full URL for the provider’s /dc endpoint and uses RestTemplate.getForObject to retrieve the response.

6. Running the Example

Start the Eureka server, the provider service ( eureka-client), and this consumer project. Access http://localhost:2101/consumer in a browser or via curl; the request will be routed to a healthy provider instance and the response from /dc will be returned.

For a Consul‑based version, refer to the corresponding consul-client and consul-consumer repositories.