eureka unknownHostException in service discovery

Question

I've two microservices,

1. eureka-client-1 running on localhost:8081
2. eureka-client-2 running on localhost:8082

Both these are DiscoveryClients registered with 'eureka-server' running on localhost:8761.

In code snippet below, I'm trying to call eureka-client-2 from eureka-client-1. Instead of calling http://localhost:8082, i want to call http://eureka-client-2 but this throws java.net.UnknownHostException during Eureka service discovery.

After searching, I found that i need to use "Brixton" to get it done.

Is there a way to do it with Camden.SR3 ?

Please suggest.

@Component
public class HystrixDemoService {   

    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }

    @HystrixCommand(fallbackMethod = "getFallbackCustomerName")
    public String getCustomerName() {
        RestTemplate restTemplate = new RestTemplate();
        URI uri = URI.create("http://eureka-client-2");     // fails here
        return restTemplate.getForObject(uri, String.class);
    }

    public String getFallbackCustomerName() {
        System.out.println("coming inside fallback method");
        return "Resillient Customer";
    }
}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>demo-pranay-eureka-client1</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>demo-pranay-eureka-client1</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.4.2.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <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.cloud</groupId>
            <artifactId>spring-cloud-starter-hystrix</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Camden.SR3</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>


</project>

application.properties for client 1, similar for client 2(just change in name i.e. eureka-client-2)

spring.application.name=eureka-client-1
server.port=8081
eureka:
  client:
    registerWithEureka: true
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
  instance:
    leaseRenewalIntervalInSeconds: 10
    statusPageUrlPath: /info
    healthCheckUrlPath: /health

application.properties for eureka server

spring.application.name=eureka-service
server.port=8761
eureka:
  client:
    registerWithEureka: false
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
  instance:
    leaseRenewalIntervalInSeconds: 10
    statusPageUrlPath: /info
    healthCheckUrlPath: /health

Answer 1

The solution is that you miss @LoadBalanced.
if you use Spring Boot or Sprint Cloud, I prefer to use the RestTemplateBuilder builder

  @Bean
  @LoadBalanced
  public RestTemplate restTemplate(RestTemplateBuilder builder) {
    return builder.build();
  }

If you use spring only, I suggest you to new RestTemplate()

  @Bean
  @LoadBalanced
  public RestTemplate restTemplate() {
      return new RestTemplate();
  }

Answer 2

For me the only thing that I need to do to fix the issue was to add the spring annotation @LoadBalanced to

@Bean
@LoadBalanced
public RestTemplate restTemplate() {
    return new RestTemplate();
}

Answer 3

Changes below worked for me.

@SpringBootApplication
public class DemoPranayEurekaClient1Application {
    public static void main(String[] args) {
        SpringApplication.run(DemoPranayEurekaClient1Application.class, args);
    }
}

@EnableDiscoveryClient
@EnableCircuitBreaker
@RestController
class HystrixDemoApplication {
    @Autowired
    HystrixDemoService hystrixDemoService;

    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }

    @RequestMapping("/")
    public String name() {
        String str = hystrixDemoService.getCustomerName();
        return "I'm A talking to "+str;
    }

}

Below is the line of code that is used for choosing instance of eureka-client-2...

ServiceInstance instance = loadBalancer.choose("eureka-client-2");

@Component
public class HystrixDemoService {

    @Autowired
    private LoadBalancerClient loadBalancer;

    @HystrixCommand(fallbackMethod = "getFallbackCustomerName")
    public String getCustomerName() {
        RestTemplate restTemplate = new RestTemplate();
        ServiceInstance instance = loadBalancer.choose("eureka-client-2");
        URI uri = instance.getUri();
        return restTemplate.getForObject(uri, String.class);
    }

    public String getFallbackCustomerName() {
        System.out.println("coming inside fallback method");
        return "Resillient Customer";
    }
}

Answer 4

As commented earlier I believe you might be missing Ribbon configuration in eureka-client-1.

First, I would move:

@Bean
@LoadBalanced
public RestTemplate restTemplate() {
    return new RestTemplate();
}

to a configuration class.

Add Ribbon configuration to application.yml, something like:

the-eureka-client-2:
   ribbon:
     # Eureka vipAddress of the target service
     DeploymentContextBasedVipAddresses: eureka-client-2

     #listOfServers: localhost:${SERVER.PORT}
     NIWSServerListClassName: com.netflix.niws.loadbalancer.DiscoveryEnabledNIWSServerList

     # Interval to refresh the server list from the source (ms)
     ServerListRefreshInterval: 30000

Inject restTemplate in HystrixDemoService class instead of instantiating a new one for every request. RestTemplate is thread-safe:

@Component
public class HystrixDemoService {   

    @Autowired
    public RestTemplate restTemplate;
...
    @HystrixCommand(fallbackMethod = "getFallbackCustomerName")
    public String getCustomerName() {
      URI uri = URI.create("http://eureka-client-2");
      return this.restTemplate.getForObject(uri, String.class);
    }

where the-eureka-client-2 is a key that maps to the registered service with name: eureka-client-2

I blogged about Microservices Registration and Discovery using Spring Cloud Eureka, Ribbon and Feign which also includes source code of the Discovery server and two clients developed using Jersey 1 and Spring MVC.