在dubbo项目中, zookeeper即注册中心帮我们实现了调度和负载均衡的能力, 这种方式被称为服务器端的负载均衡, springcloud中, 使用ribben实现的客户端负载均衡

什么是ribbon?

Ribbon是Netflix发布的云中间层服务开源项目，其主要功能是提供客户端侧负载均衡算法。Ribbon客户端组件提供一系列完善的配置项如连接超时，重试等。简单的说，Ribbon是一个客户端负载均衡器，我们可以在配置文件中列出Load Balancer后面所有的机器，Ribbon会自动的帮助你基于某种规则（如简单轮询，随机连接等）去连接这些机器，我们也很容易使用Ribbon实现自定义的负载均衡算法。

eureka使用ribbon的大致架构

Ribbon工作时分为两步：第一步先选择 Eureka Server, 它优先选择在同一个Zone且负载较少的Server；第二步再根据用户指定的策略，在从Server取到的服务注册列表中选择一个地址。其中Ribbon提供了多种策略，例如轮询round robin、随机Random、根据响应时间加权等。

通过代码实现:

将刚才的cosumer-movie改造成ribbon的项目

添加一个注解类, 需要放置在mainClass扫描不到的包下, 或者在mainClass中通过@COmponentScan进行过滤

这儿使用的是注解过滤, 所以首先需要一个注解:

package com.wenbronk.cosumer.ribben.annotation;

/**
 * 自定义注解, 排除不想被扫描到的内容
 * Created by wenbronk on 2017/5/18.
 */
public @interface ExcudeAnnotation {
}

然后是一个ribbon的注解声明类:

package com.wenbronk.cosumer.ribben.config;

import com.netflix.loadbalancer.IRule;
import com.netflix.loadbalancer.RandomRule;
import com.wenbronk.cosumer.ribben.annotation.ExcudeAnnotation;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * 默认规则为轮询, 这个为随机规则
 * 该类必须放置在扫描不到的包下, 或者添加排除, 虽然他必须有注解
 * Created by wenbronk on 2017/5/18.
 */
@Configuration
@ExcudeAnnotation
public class MyRibbonConfig {

    @Bean
    public IRule ribbonRule() {
        return new RandomRule();
    }

}

在mainClass中进行过滤

package com.wenbronk.cosumer.ribben;

import com.wenbronk.cosumer.ribben.annotation.ExcudeAnnotation;
import com.wenbronk.cosumer.ribben.config.MyRibbonConfig;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.ribbon.RibbonClient;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.FilterType;
import org.springframework.web.client.RestTemplate;

/**
 * 通过RIbbonClient自定义ribbon客户端
 * Created by root on 2017/5/18.
 */
@SpringBootApplication
@EnableEurekaClient
// 使用此规则不可放在 可扫描的路径下, 如果非要放置, 需要加自定义注解
@RibbonClient(name = "microserver-provider-user", configuration = MyRibbonConfig.class)
@ComponentScan(excludeFilters = {@ComponentScan.Filter(type = FilterType.ANNOTATION, value = {ExcudeAnnotation.class})})
public class MovieRibbenApplication {

    /**
     * 使用LoadBalanced开启客户端负载均衡的功能
     * @return
     */
    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }

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

}

验证:

通过配置端口, 将user服务启动4个实例, 并注册为2个服务, 在movie-ribbon的controller中加入如下代码

package com.wenbronk.cosumer.ribben.controller;

import com.wenbronk.cosumer.ribben.entity.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.loadbalancer.LoadBalancerClient;
import org.springframework.web.bind.annotation.GetMapping;
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;

/**
 * Created by root on 2017/5/18.
 */
@RestController
public class MovieRibbenController {

    @Autowired
    private RestTemplate restTemplate;

    @Autowired
    private LoadBalancerClient loadBalancerClient;

    @RequestMapping("/movie/{id}")
    public User findById(@PathVariable Long id) {
        return restTemplate.getForObject("http://microservice-provider-user/simple/" + id, User.class);
    }

    @GetMapping("/test")
    public void test() {
        ServiceInstance instance = this.loadBalancerClient.choose("MICROSERVICE-PROVIDER-USER");
        System.out.println("111: " + instance.getServiceId() + ": " + instance.getHost() + ": " + instance.getPort());
//        System.out.println(instance.toString());

        ServiceInstance instance1 = this.loadBalancerClient.choose("MICROSERVICE-PROVIDER-USER-1");
        System.out.println("222: " + instance1.getServiceId() + ": " + instance1.getHost() + ": " + instance1.getPort());
//        System.out.println(instance1);
//        System.out.println(instance == instance1);
    }
}

通过浏览器重复的发送请求, 在控制台可看到只有provide-user 使用了我们自定义的规则, user-1 仍然使用的ribbon的默认规则轮询

通过配置文件的方式, 自定义ribbonclient:

从版本1.2.0开始，Spring Cloud Netflix现在支持使用属性与Ribbon文档兼容来自定义Ribbon客户端。

配置的优先级: 配置文件 >  java代码 > springcloud default

配置文件配置, 只需要在yml‘中添加如下内容

users:
  ribbon:
    NFLoadBalancerRuleClassName: com.netflix.loadbalancer.WeightedResponseTimeRule

NFLoadBalancerRuleClassName 是规则, 除了此规则 springcloud还有

每个规则可添加的类也有很多 

mainClass.java

package com.wenbronk.cosumer.ribbon.yml;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

/**
 * Created by wenbronk on 2017/5/20.
 */
@SpringBootApplication
@EnableEurekaClient
public class MoveiRibbonYmlApplicatoin {

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

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

MovieRibbonController

package com.wenbronk.cosumer.ribbon.yml.controller;

import com.wenbronk.cosumer.ribbon.yml.entity.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.loadbalancer.LoadBalancerClient;
import org.springframework.web.bind.annotation.GetMapping;
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;

/**
 * Created by root on 2017/5/18.
 */
@RestController
public class MovieRibbenController {

    @Autowired
    private RestTemplate restTemplate;

    @Autowired
    private LoadBalancerClient loadBalancerClient;

    @RequestMapping("/movie/{id}")
    public User findById(@PathVariable Long id) {
        return restTemplate.getForObject("http://microservice-provider-user/simple/" + id, User.class);
    }

    @GetMapping("/test")
    public void test() {
        ServiceInstance instance = this.loadBalancerClient.choose("MICROSERVICE-PROVIDER-USER");
        System.out.println("111: " + instance.getServiceId() + ": " + instance.getHost() + ": " + instance.getPort());
//        System.out.println(instance.toString());

        ServiceInstance instance1 = this.loadBalancerClient.choose("MICROSERVICE-PROVIDER-USER-1");
        System.out.println("222: " + instance1.getServiceId() + ": " + instance1.getHost() + ": " + instance1.getPort());
//        System.out.println(instance1);
//        System.out.println(instance == instance1);
    }
}