Eureka Service Discovery example

When you are running multiple microservices, you need a mechanism to locate a service. You can register each microservice in a service registry which is a seperate service. A service registry also helps in loadbalancing, and register or unregister a service when it is not available. A service or client application which wants to use another service can lookup the service in the service registry and then call it.

Below Eureka Service Discovery example shows how to register and lookup a microservice using Netflix Eureka service registry. We will create a Eureka Service Registry server and register two microservices named ToyService and ToyClientService respectively. ToyClientService microservice will lookup ToyService microservice in the Eureka Service Registry and invoke its exposed endpoint.

<parent>
    <groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-parent</artifactId>
	<version>2.6.3</version>
	<relativePath/> 
</parent>
    
<dependencies>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
    </dependency>
</dependencies>

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-dependencies</artifactId>
            <version>2021.0.3</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

Step 2) Create EurekaServiceApplication class to launch Eureka Service registry

You need to add @EnableEurekaServer annotation to make sure that the application will run as Eureka server.

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

@EnableEurekaServer
@SpringBootApplication
public class EurekaServiceApplication {

  public static void main(String[] args) {
    SpringApplication.run(EurekaServiceApplication.class, args);
  }
}  

Step 3) Create application.yml file under src/main/resources

Since the application will run as service registry, we will not register it with service registry by setting register-with-eureka: false.

server:
  port: 8761
  
spring:  
  application:
    name: discovery-service

eureka:
  client:
    register-with-eureka: false
    fetch-registry: false

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>

package com.example.demo;

    public class Toy {
        
        private String name;
        private String type;
        private double price;
        
        public Toy(String name, String type, float price) {
            this.name = name;
            this.type = type;
            this.price = price;
        }
    
    //removed getter setter for brevity
   
}   

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class ToyServiceApplication {

    public static void main(String[] args) {
        SpringApplication.run(ToyServiceApplication.class, args);
    }
}   

package com.example.demo;

import java.util.ArrayList;
import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class ToyRestController {

    private static final Logger LOG = LoggerFactory.getLogger(ToyRestController.class);

    private List<Toy> toys = new ArrayList<>();

    public ToyRestController() {
        toys.add(new Toy("Barbie", "Doll", 45.0));
        toys.add(new Toy("My Little Pony", "Animal", 10.4));
        toys.add(new Toy("Hot Wheels", "Car", 5.4));
    }

    @RequestMapping(value = "/toys") // http://localhost:8090/toys
    public List<Toy> listAll() {
        LOG.info("returning list of toys");
        return toys;
    }
	
    @RequestMapping(value = "/toys/{id}") // http://localhost:8090/toys/1
    public Toy getToy(@PathVariable int id) {
        LOG.info("returning toy");
        return toys.get(id);
    }

}  

spring:
  application:
    name: toy-service

server:
  port: 8090
  
eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/      

<groupId>com.example</groupId>
<artifactId>toy-client-service</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>        

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@SpringBootApplication
public class ToyClientServiceApplication {

    public static void main(String[] args) {
        SpringApplication.run(ToyClientServiceApplication.class, args);
    }
    
    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
} 

package com.example.demo;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

@RestController
public class ToyClientServiceRestController {
	
    @Autowired
    private RestTemplate restTemplate;

    private static final Logger LOG = LoggerFactory.getLogger(ToyClientServiceRestController.class);

    @RequestMapping("/toy-client-service/toys") // http://localhost:8090/toys
    public ResponseEntity<?> getToys() {
		LOG.info("calling toy service");
        return restTemplate.getForEntity("http://toy-service/toys/", String.class);
    }
	
    @RequestMapping("/toy-client-service/{id}") // http://localhost:8090/toys/1
    public ResponseEntity<?> getToy(@PathVariable String id) {
		LOG.info("calling toy service");
        return restTemplate.getForEntity("http://toy-service/toys/"+id, String.class);
    }
        
} 

spring:
  application:
    name: toy-client-service

server:
  port: 8091
  
eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/