博客

一、负载规则替换

• 1.修改cloud-consumer-order80
• 2.注意配置细节

官方文档明确给出了警告:

这个自定义配置类不能放在@ComponentScan所扫描的当前包下以及子包下，否则我们自定义的这个配置类就会被所有的Ribbon客户端所共享，达不到特殊化定制的目的了。（也就是说不要将Ribbon配置类与主启动类同包）

• 3.新建package – com.lun.myrule

• 4.在com.lun.myrule下新建MySelfRule规则类

import com.netflix.loadbalancer.IRule;
import com.netflix.loadbalancer.RandomRule;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MySelfRule {

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

• 5.主启动类添加@RibbonClient

import com.lun.myrule.MySelfRule;
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;

@SpringBootApplication
@EnableEurekaClient
//添加到此处
@RibbonClient(name = "CLOUD-PAYMENT-SERVICE", configuration = MySelfRule.class)
public class OrderMain80
{
    public static void main( String[] args ){
        SpringApplication.run(OrderMain80.class, args);
    }
}

• 6.测试

开启cloud-eureka-server7001，cloud-consumer-order80，cloud-provider-payment8001，cloud-provider-payment8002

浏览器-输入http://localhost/consumer/payment/get/1

返回结果中的serverPort在8001与8002两种间反复横跳。

二、默认负载轮询算法原理

默认负载轮训算法:

rest接口第几次请求数 % 服务器集群总数量 = 实际调用服务器位置下标

，每次

服务重启动后rest接口计数从1开始

。


List instances = discoveryClient.getInstances(“CLOUD-PAYMENT-SERVICE”);

• List [0] instances = 127.0.0.1:8002
• List [1] instances = 127.0.0.1:8001

8001+ 8002组合成为集群，它们共计2台机器，集群总数为2，按照轮询算法原理：

• 当总请求数为1时:1%2=1对应下标位置为1，则获得服务地址为127.0.0.1:8001
• 当总请求数位2时:2%2=О对应下标位置为0，则获得服务地址为127.0.0.1:8002
• 当总请求数位3时:3%2=1对应下标位置为1，则获得服务地址为127.0.0.1:8001
• 当总请求数位4时:4%2=О对应下标位置为0，则获得服务地址为127.0.0.1:8002
  
  如此类推…

三、RoundRobinRule源码分析

public interface IRule{
    /*
     * choose one alive server from lb.allServers or
     * lb.upServers according to key
     * 
     * @return choosen Server object. NULL is returned if none
     *  server is available 
     */

    //重点关注这方法
    public Server choose(Object key);
    
    public void setLoadBalancer(ILoadBalancer lb);
    
    public ILoadBalancer getLoadBalancer();    
}

package com.netflix.loadbalancer;

import com.netflix.client.config.IClientConfig;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * The most well known and basic load balancing strategy, i.e. Round Robin Rule.
 *
 * @author stonse
 * @author Nikos Michalakis <nikos@netflix.com>
 *
 */
public class RoundRobinRule extends AbstractLoadBalancerRule {

    private AtomicInteger nextServerCyclicCounter;
    private static final boolean AVAILABLE_ONLY_SERVERS = true;
    private static final boolean ALL_SERVERS = false;

    private static Logger log = LoggerFactory.getLogger(RoundRobinRule.class);

    public RoundRobinRule() {
        nextServerCyclicCounter = new AtomicInteger(0);
    }

    public RoundRobinRule(ILoadBalancer lb) {
        this();
        setLoadBalancer(lb);
    }

    //重点关注这方法。
    public Server choose(ILoadBalancer lb, Object key) {
        if (lb == null) {
            log.warn("no load balancer");
            return null;
        }

        Server server = null;
        int count = 0;
        while (server == null && count++ < 10) {
            List<Server> reachableServers = lb.getReachableServers();
            List<Server> allServers = lb.getAllServers();
            int upCount = reachableServers.size();
            int serverCount = allServers.size();

            if ((upCount == 0) || (serverCount == 0)) {
                log.warn("No up servers available from load balancer: " + lb);
                return null;
            }

            int nextServerIndex = incrementAndGetModulo(serverCount);
            server = allServers.get(nextServerIndex);

            if (server == null) {
                /* Transient. */
                Thread.yield();
                continue;
            }

            if (server.isAlive() && (server.isReadyToServe())) {
                return (server);
            }

            // Next.
            server = null;
        }

        if (count >= 10) {
            log.warn("No available alive servers after 10 tries from load balancer: "
                    + lb);
        }
        return server;
    }

    /**
     * Inspired by the implementation of {@link AtomicInteger#incrementAndGet()}.
     *
     * @param modulo The modulo to bound the value of the counter.
     * @return The next value.
     */
    private int incrementAndGetModulo(int modulo) {
        for (;;) {
            int current = nextServerCyclicCounter.get();
            int next = (current + 1) % modulo;//求余法
            if (nextServerCyclicCounter.compareAndSet(current, next))
                return next;
        }
    }

    @Override
    public Server choose(Object key) {
        return choose(getLoadBalancer(), key);
    }

    @Override
    public void initWithNiwsConfig(IClientConfig clientConfig) {
    }
}