Spring Cloud Eureka服务注册源码分析

Eureka是怎么work的

那eureka client如何将本地服务的注册信息发送到远端的注册服务器eureka server上。通过下面的源码分析，看出Eureka Client的定时任务调用Eureka Server的Reset接口，而Eureka接收到调用请求后会处理服务的注册以及Eureka Server中的数据同步的问题。

服务注册

源码分析，看出服务注册可以认为是Eureka client自己完成，不需要服务本身来关心。

Eureka Client的定时任务调用Eureka Server的提供接口

在com.netflix.discovery.DiscoveryClient启动的时候，会初始化一个定时任务，定时的把本地的服务配置信息，即需要注册到远端的服务信息自动刷新到注册服务器上。
首先看一下Eureka的代码，在spring-cloud-netflix-eureka-server工程中可以找到这个依赖eureka-client-1.4.11.jar查看代码可以看到，
com.netflix.discovery.DiscoveryClient.java中的1240行可以看到Initializes all scheduled tasks，在1277行，可以看到InstanceInfoReplicator定时任务

在DiscoveryClient中初始化一个InstanceInfoReplicator，其实里面封装了以定时任务。

/**
     * Initializes all scheduled tasks.
     */
    private void initScheduledTasks() {
        if (clientConfig.shouldFetchRegistry()) {
            // registry cache refresh timer
            int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
            int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
            scheduler.schedule(
                    new TimedSupervisorTask(
                            "cacheRefresh",
                            scheduler,
                            cacheRefreshExecutor,
                            registryFetchIntervalSeconds,
                            TimeUnit.SECONDS,
                            expBackOffBound,
                            new CacheRefreshThread()
                    ),
                    registryFetchIntervalSeconds, TimeUnit.SECONDS);
        }
        if (clientConfig.shouldRegisterWithEureka()) {
            int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
            int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
            logger.info("Starting heartbeat executor: " + "renew interval is: " + renewalIntervalInSecs);
            // Heartbeat timer
            scheduler.schedule(
                    new TimedSupervisorTask(
                            "heartbeat",
                            scheduler,
                            heartbeatExecutor,
                            renewalIntervalInSecs,
                            TimeUnit.SECONDS,
                            expBackOffBound,
                            new HeartbeatThread()
                    ),
                    renewalIntervalInSecs, TimeUnit.SECONDS);
            // InstanceInfo replicator
            /**************************封装了定时任务**********************************/
            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);
            }
            //点击可以查看start方法
            instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
        } else {
            logger.info("Not registering with Eureka server per configuration");
        }
    }

EurekaHttpClient ：提供eureka 的客户端API方法