Load Balancing in Spring Cloud mit Ribbon und Beispiel verstehen

<?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>org.o7planning</groupId>
    <artifactId>SpringCloudLoadBalancerRibbon</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>SpringCloudLoadBalancerRibbon</name>
    <description>Spring Cloud Load Balancer (Ribbon)</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.9.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>
        <spring-cloud.version>Edgware.RELEASE</spring-cloud.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.cloud</groupId>
            <artifactId>spring-cloud-starter-ribbon</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-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</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>

spring:
  application:
    name: XYZ-SERVICE
 
server:
  port: 5555

# -- Configure for Ribbon:
 
ping-server:
  ribbon:
    eureka:
      enabled: false # Disable Default Ping
    listOfServers: localhost:8000,localhost:8001,localhost:8002,,localhost:8003
    ServerListRefreshInterval: 15000
    
# -- Configure Discovery Client (Eureka Client).    
# Configure this application to known "Service Registration".

eureka:
  instance:
    appname: XYZ-SERVICE  # ==> This is an instance of XYZ-SERVICE
  client:    
    fetchRegistry: true
    serviceUrl:
#      defaultZone: http://my-eureka-server.com:9000/eureka
      defaultZone: http://my-eureka-server-us.com:9001/eureka
#      defaultZone: http://my-eureka-server-fr.com:9002/eureka
#      defaultZone: http://my-eureka-server-vn.com:9003/eureka

package org.o7planning.ribbon;

import org.o7planning.ribbon.config.RibbonConfiguration;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.ribbon.RibbonClient;

@RibbonClient(name = "ping-a-server", configuration = RibbonConfiguration.class)
@EnableEurekaClient
@SpringBootApplication
public class SpringCloudLoadBalancerRibbonApplication {

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

}

package org.o7planning.ribbon.config;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;

import com.netflix.client.config.IClientConfig;
import com.netflix.loadbalancer.IPing;
import com.netflix.loadbalancer.IRule;
import com.netflix.loadbalancer.PingUrl;
import com.netflix.loadbalancer.WeightedResponseTimeRule;

 
public class RibbonConfiguration {
    
    @Autowired
    private IClientConfig ribbonClientConfig;
 
    @Bean
    public IPing ribbonPing(IClientConfig config) {
        return new PingUrl();
    }
 
    @Bean
    public IRule ribbonRule(IClientConfig config) {
        return new WeightedResponseTimeRule();
    }
    
}

package org.o7planning.ribbon.controller;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.discovery.DiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalancerClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

@RestController
public class Example1Controller {

    @Autowired
    private DiscoveryClient discoveryClient;

    @Autowired
    private LoadBalancerClient loadBalancer;

    @ResponseBody
    @RequestMapping(value = "/", method = RequestMethod.GET)
    public String home() {

        return "<a href='testCallAbcService'>/testCallAbcService</a>";
    }

    @ResponseBody
    @RequestMapping(value = "/testCallAbcService", method = RequestMethod.GET)
    public String showFirstService() {

        String serviceId = "ABC-SERVICE".toLowerCase();

        // (Need!!) eureka.client.fetchRegistry=true
        List<ServiceInstance> instances = this.discoveryClient.getInstances(serviceId);

        if (instances == null || instances.isEmpty()) {
            return "No instances for service: " + serviceId;
        }
        String html = "<h2>Instances for Service Id: " + serviceId + "</h2>";

        for (ServiceInstance serviceInstance : instances) {
            html += "<h3>Instance :" + serviceInstance.getUri() + "</h3>";
        }

        // Create a RestTemplate.
        RestTemplate restTemplate = new RestTemplate();

        html += "<br><h4>Call /hello of service: " + serviceId + "</h4>";

        try {
            // May be throw IllegalStateException (No instances available)
            ServiceInstance serviceInstance = this.loadBalancer.choose(serviceId);

            html += "<br>===> Load Balancer choose: " + serviceInstance.getUri();

            String url = "http://" + serviceInstance.getHost() + ":" + serviceInstance.getPort() + "/hello";

            html += "<br>Make a Call: " + url;
            html += "<br>";

            String result = restTemplate.getForObject(url, String.class);

            html += "<br>Result: " + result;
        } catch (IllegalStateException e) {
            html += "<br>loadBalancer.choose ERROR: " + e.getMessage();
            e.printStackTrace();
        } catch (Exception e) {
            html += "<br>Other ERROR: " + e.getMessage();
            e.printStackTrace();
        }
        return html;
    }

}