巡山小妖007

个人站

欢迎来到我的个人博客~


SpringCloud-Eureka-服务注册是如何发起的

​ Spring Cloud环境下,服务提供者和消费者启动后都会将自身注册到Eureka

一、将服务注册到Eureka 一个SpringBoot应用如果要注册到Spring Cloud环境(Greenwich.SR3版本),步骤很简单:

  • pom.xml中添加启动器:spring-cloud-starter-netflix-eureka-client;

  • 增加配置:eureka.client.serviceUrl.defaultZone: http://localhost:8100/eureka/;

  • 启动应用;

  • 如果注册中心正常,此时就能在注册中心发现这个应用了,如下图红框所示:

eureka-web

  • 按照spring.factories中的配置,EurekaClientAutoConfiguration中的配置都会生效,包括下面这段代码返回的bean:

  • @Bean
    public DiscoveryClient discoveryClient(EurekaInstanceConfig config, EurekaClient client) {
        return new EurekaDiscoveryClient(config, client);
    }
    
  • spring容器初始化时会实例化所有单例bean,就会执行EurekaClientAutoConfiguration的discoveryClient方法获取这个bean实例,于是就构造了一个EurekaDiscoveryClient对象;

  • 注意EurekaDiscoveryClient的构造方法,第二个入参是com.netflix.discovery.EurekaClient类型,此对象同样来自EurekaClientAutoConfiguration类,如下方法:

  • @Bean(destroyMethod = "shutdown")
    @ConditionalOnMissingBean(value = EurekaClient.class, search = SearchStrategy.CURRENT)
    @org.springframework.cloud.context.config.annotation.RefreshScope
    @Lazy
    public EurekaClient eurekaClient(ApplicationInfoManager manager, EurekaClientConfig config, EurekaInstanceConfig instance) {
        manager.getInfo(); // force initialization
        return new CloudEurekaClient(manager, config, this.optionalArgs,this.context);
    }
    
  • CloudEurekaClient的父类com.netflix.discovery.DiscoveryClient来自netflix发布的eureka-client包中,所以可以这么理解:EurekaDiscoveryClient类是个代理身份,真正的服务注册发现是委托给netflix的开源包来完成的,我们可以专心的使用SpringCloud提供的服务注册发现功能,只需要知道EurekaDiscoveryClient即可,真正的服务是eureka-client来完成的;

  • 接下来需要关注com.netflix.discovery.DiscoveryClient的构造方法,因为这里面有服务注册的逻辑,整个构造方法内容太多,无需都细看,只看关键代码即可;

  • DiscoveryClient的构造方法中,最熟悉的应该是下图红框中这段日志输出的了:

    对应的应用启动日志中就有这段日志输出,如下图红框:

    红框中的”us-east-1”,是默认的region,来自配置类EurekaClientConfigBean,这里面有各种eureka相关的配置信息,以及默认配置,如下图:

  • 继续看DiscoveryClient的构造方法,服务注册相关的initScheduledTasks方法在此被调用,如下图:

  • initScheduledTasks方法的内容如下,请注意中文注释:

        private void initScheduledTasks() {
            //获取服务注册列表信息
            if (clientConfig.shouldFetchRegistry()) {
                //服务注册列表更新的周期时间
                int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
                int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
                //定时更新服务注册列表
                scheduler.schedule(
                        new TimedSupervisorTask(
                                "cacheRefresh",
                                scheduler,
                                cacheRefreshExecutor,
                                registryFetchIntervalSeconds,
                                TimeUnit.SECONDS,
                                expBackOffBound,
                                new CacheRefreshThread() //该线程执行更新的具体逻辑
                        ),
                        registryFetchIntervalSeconds, TimeUnit.SECONDS);
            }
            if (clientConfig.shouldRegisterWithEureka()) {
                //服务续约的周期时间
                int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
                int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
                //应用启动可见此日志,内容是:Starting heartbeat executor: renew interval is: 30
                logger.info("Starting heartbeat executor: " + "renew interval is: " + renewalIntervalInSecs);
                // 定时续约
                scheduler.schedule(
                        new TimedSupervisorTask(
                                "heartbeat",
                                scheduler,
                                heartbeatExecutor,
                                renewalIntervalInSecs,
                                TimeUnit.SECONDS,
                                expBackOffBound,
                                new HeartbeatThread() //该线程执行续约的具体逻辑
                        ),
                        renewalIntervalInSecs, TimeUnit.SECONDS);
      
                //这个Runable中含有服务注册的逻辑
                instanceInfoReplicator = new InstanceInfoReplicator(
                        this,
                        instanceInfo,
                        clientConfig.getInstanceInfoReplicationIntervalSeconds(),
                        2); // burstSize
      
                statusChangeListener = new ApplicationInfoManager.StatusChangeListener() {
                    @Override
                    public String getId() {
                        return "statusChangeListener";
                    }
      
                    @Override
                    public void notify(StatusChangeEvent statusChangeEvent) {
                        if (InstanceStatus.DOWN == statusChangeEvent.getStatus() ||
                                InstanceStatus.DOWN == statusChangeEvent.getPreviousStatus()) {
                            // log at warn level if DOWN was involved
                            logger.warn("Saw local status change event {}", statusChangeEvent);
                        } else {
                            logger.info("Saw local status change event {}", statusChangeEvent);
                        }
                        instanceInfoReplicator.onDemandUpdate();
                    }
                };
      
                if (clientConfig.shouldOnDemandUpdateStatusChange()) {
                    applicationInfoManager.registerStatusChangeListener(statusChangeListener);
                }
                //服务注册
                instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
            } else {
                logger.info("Not registering with Eureka server per configuration");
            }
        }
    

    上述代码中有几处需要注意,这些关键点在后面的章节将继续展开: a. 周期性更新服务列表; b. 周期性服务续约; c. 服务注册逻辑被放入Runnable实现类InstanceInfoReplicator之中,在新线程中执行;

打赏一个呗

取消

感谢您的支持,我会继续努力的!

扫码支持
扫码支持
扫码打赏,你说多少就多少

打开支付宝扫一扫,即可进行扫码打赏哦