Ribbon可以实现客户端的负载均衡和故障转移，默认情况下，Ribbon使用到的负载均衡算法是轮询算法

下面是Ribbon实现客户端负载均衡的列子

使用到的项目有spring-cloud-eureka,spring-cloud-provider-01,spring-cloud-provider-02,spring-cloud-consumer-01

服务提供端

spring-cloud-provider-01

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>spring-cloud-provider-01</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>spring-cloud-provider-01</name>
    <description>Demo project for Spring Boot</description>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.4.7.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>Camden.SR7</spring-cloud.version>
    </properties>
    <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>
        <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>

application.yaml

server:
  port: 8080
spring:
  application:
    name: spring-cloud-provider
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka
  instance:
    prefer-ip-address: true

User.java

package com.example.demo.model;
import java.util.Date;
public class User {
    private String id;
    private String userName;
    private int age;
    private Date birthday;
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getUserName() {
        return userName;
    }
    public void setUserName(String userName) {
        this.userName = userName;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public Date getBirthday() {
        return birthday;
    }
    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
    public User(String id, String userName, int age, Date birthday) {
        super();
        this.id = id;
        this.userName = userName;
        this.age = age;
        this.birthday = birthday;
    }
    public User(String id, String userName, int age) {
        super();
        this.id = id;
        this.userName = userName;
        this.age = age;
    }
}

UserController.java

package com.example.demo.controller;
import java.util.HashMap;
import java.util.Map;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

import com.example.demo.model.User;

@RestController
@RequestMapping(value="/user")
public class UserController {
    private Map<String, User> umap = new HashMap();
    public UserController(){
        umap.put("1", new User("1", "xiaoming1", 30));
        umap.put("2", new User("2", "xiaohong1", 20));
        umap.put("3", new User("3", "zhangsan1", 80));
        umap.put("4", new User("4", "lisi1", 10));
        umap.put("5", new User("5", "wangwu1", 22));
    }
    @GetMapping(value="/get")
    @ResponseBody
    public User get(String id){
        return umap.get(id);
    }
}

spring-cloud-provider-02

spring-cloud-provider-01和spring-cloud-provider-02不同的地方是UserController
其他地方都是一样

UserController.java

package com.example.demo.controller;
import java.util.HashMap;
import java.util.Map;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

import com.example.demo.model.User;

@RestController
@RequestMapping(value="/user")
public class UserController {
    private Map<String, User> umap = new HashMap();
    public UserController(){
        umap.put("1", new User("1", "xiaoming", 30));
        umap.put("2", new User("2", "xiaohong", 20));
        umap.put("3", new User("3", "zhangsan", 80));
        umap.put("4", new User("4", "lisi", 10));
        umap.put("5", new User("5", "wangwu", 22));
    }
    @GetMapping(value="/get")
    @ResponseBody
    public User get(String id){
        return umap.get(id);
    }
}

服务消费端

spring-cloud-consumer-01

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>spring-cloud-consumer-01</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>spring-cloud-consumer-01</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.4.7.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>Camden.SR7</spring-cloud.version>
    </properties>

    <dependencies>
        <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>

application.yaml

server:
  port: 8082

spring:
  application:
    name: spring-cloud-consumer
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka
  instance:
    prefer-ip-address: true

SpringCloudConsumer01Application.java

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
@EnableEurekaClient
@SpringBootApplication
public class SpringCloudConsumer01Application {

    public static void main(String[] args) {
        SpringApplication.run(SpringCloudConsumer01Application.class, args);
    }
}

CoreConfiguration.java

package com.example.demo.config;

import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Controller;
import org.springframework.web.client.RestTemplate;

@Controller
public class CoreConfiguration {
    @LoadBalanced
    @Bean
    public RestTemplate restTemplateBean(){
        return new RestTemplate();
    }

}

UserConstroller.java

package com.example.demo.controller;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

import com.example.demo.model.User;
@RestController
@RequestMapping(value="/user")
public class UserConstroller {
    @Autowired
    private RestTemplate restTemplate;
    @ResponseBody
    @GetMapping("/get")
    public User get(String uid){
        return restTemplate.getForObject("http://spring-cloud-provider/user/get?id="+uid, User.class);
    }

}

User.java

package com.example.demo.model;

import java.util.Date;

public class User {

    private String id;
    private String userName;
    private int age;
    private Date birthday;
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getUserName() {
        return userName;
    }
    public void setUserName(String userName) {
        this.userName = userName;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public Date getBirthday() {
        return birthday;
    }
    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
    public User(String id, String userName, int age, Date birthday) {
        super();
        this.id = id;
        this.userName = userName;
        this.age = age;
        this.birthday = birthday;
    }
    public User(String id, String userName, int age) {
        super();
        this.id = id;
        this.userName = userName;
        this.age = age;
    }
    public User(){}
}

验证消费端

http://192.168.88.101:8082/user/get?uid=1

在浏览器中打开http://192.168.88.101:8082/user/get?uid=1，并且不停的刷新，页面中轮回显示下面的内容：

{"id":"1","userName":"xiaoming1","age":30,"birthday":null}
{"id":"1","userName":"xiaoming","age":30,"birthday":null}

当服务提供端挂了一个的时候，可以实现故障转移