spring cloud学习（五）-手写Ribbo负载均衡之轮询算法

轮询算法计算公式

• 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   
• 每次服务器重启后rest接口数从1开始

轮询算法源码分析

IRule接口

//IRule接口
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 
     */
	//选择哪个服务实例
    public Server choose(Object key);
    
    public void setLoadBalancer(ILoadBalancer lb);
    
    public ILoadBalancer getLoadBalancer();    
}

 

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);
    }

    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;
            if (nextServerCyclicCounter.compareAndSet(current, next))
                return next;
        }
    }

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

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

手写轮询算法：

• 启动eureka服务中心集群（7001与7002）
• 改造8001与8002服务的提供者

@GetMapping("/payment/lb")
    public String getPaymentLB(){
        return serverPort;
}

• 改造80端口：去掉主程序中的@RibbonClient(name = "CLOUD-PAYMENT-SERVICE",configuration = MyIRule.class)
• 不使用ribbon自带的负载均衡，ApplicationContextConfig 去掉注解@LoadBalanced

@Configuration
public class ApplicationConfig {

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

•  新建LoadBalancer接口

public interface LoadBalancer {

    ServiceInstance instance(List<ServiceInstance> instanceList);
}

•  实现该接口

@Component
public class MyLB implements LoadBalancer {

//  原子类 接口连接此处初始值为0
    private AtomicInteger atomicInteger = new AtomicInteger(0);

    public final int getAndIncrement(){
        int current;
        int next;
        do{
            current = this.atomicInteger.get();
            next = current >= Integer.MAX_VALUE ? 0 : current + 1;
        }while (!this.atomicInteger.compareAndSet(current,next));
        System.out.println("===========>第几次访问次数"+next);
        return  next;
    }

    @Override
    public ServiceInstance instance(List<ServiceInstance> instanceList) {
        int index = getAndIncrement() % instanceList.size();
        return instanceList.get(index);
    }
}

•  重写controller

 @GetMapping("/consumer/payment/lb")
    public String getPaymentLB(){
        List<ServiceInstance> instances = discoveryClient.getInstances("CLOUD-PAYMENT-SERVICE");
        if (instances == null || instances.size() <= 0){
            return null;
        }
        ServiceInstance instance = loadBalancer.instance(instances);
        URI uri = instance.getUri();
        return restTemplate.getForObject(uri+"/payment/lb",String.class);
    }

 测试：