Eureka服务续约(Renew)源码分析
主要对Eureka的Renew(服务续约)，从服务提供者发起续约请求开始分析，通过阅读源码和画时序图的方式，展示Eureka服务续约的整个生命周期。服务续约主要是把服务续约的信息更新到自身的Eureka Server中，然后再同步到其它Eureka Server中。
Renew（服务续约）操作由Service Provider定期调用，类似于heartbeat。目的是隔一段时间Service Provider调用接口，告诉Eureka Server它还活着没挂，不要把它T了。通俗的说就是它们两之间的心跳检测，避免服务提供者被剔除掉。
Renew源码分析
服务提供者实现细节
服务提供者发发起服务续约的时序图
在com.netflix.discovery.DiscoveryClient.initScheduledTasks()中的1272行，TimedSupervisorTask会定时发起服务续约，代码如下所示:
// Heartbeat timer scheduler.schedule( new TimedSupervisorTask( "heartbeat", scheduler, heartbeatExecutor, renewalIntervalInSecs, TimeUnit.SECONDS, expBackOffBound, new HeartbeatThread() ), renewalIntervalInSecs, TimeUnit.SECONDS);
2.在com.netflix.discovery.DiscoveryClient中的1393行，有一个HeartbeatThread线程发起续约操作
private class HeartbeatThread implements Runnable { public void run() { //调用eureka-client中的renew if (renew()) { lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis(); } } }
renew()调用eureka-client-1.4.11.jarcom.netflix.discovery.DiscoveryClient中829行renew()发起PUT Reset请求，
调用com.netflix.eureka.resources.InstanceResource中的renewLease()续约。
Netflix中的Eureka Core实现细节
NetFlix中Eureka Core中的服务续约时序图，如下图所示。
打开com.netflix.eureka.resources.InstanceResource中的106行的renewLease()方法，代码如下:
private final PeerAwareInstanceRegistry registry @PUT public Response renewLease( @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication, @QueryParam("overriddenstatus") String overriddenStatus, @QueryParam("status") String status, @QueryParam("lastDirtyTimestamp") String lastDirtyTimestamp) { boolean isFromReplicaNode = "true".equals(isReplication); //调用 boolean isSuccess = registry.renew(app.getName(), id, isFromReplicaNode); //其余省略 }
点开registry.renew(app.getName(), id, isFromReplicaNode);我们可以看到，调用了org.springframework.cloud.netflix.eureka.server.InstanceRegistry中的renew（）方法，代码如下:
@Override public boolean renew(final String appName, final String serverId, boolean isReplication) { log("renew " + appName + " serverId " + serverId + ", isReplication {}" + isReplication); List<Application> applications = getSortedApplications(); for (Application input : applications) { if (input.getName().equals(appName)) { InstanceInfo instance = null; for (InstanceInfo info : input.getInstances()) { if (info.getHostName().equals(serverId)) { instance = info; break; } } publishEvent(new EurekaInstanceRenewedEvent(this, appName, serverId, instance, isReplication)); break; } } //调用com.netflix.eureka.registry.PeerAwareInstanceRegistryImpl中的renew方法 return super.renew(appName, serverId, isReplication); }
从super.renew()看到调用了父类中的com.netflix.eureka.registry.PeerAwareInstanceRegistryImpl中420行的renew()方法
public boolean renew(final String appName, final String id, final boolean isReplication) { //服务续约成功， if (super.renew(appName, id, isReplication)) { //然后replicateToPeers同步其它Eureka Server中的数据 replicateToPeers(Action.Heartbeat, appName, id, null, null, isReplication); return true; } return false; }
从上面代码中super.renew(appName, id, isReplication)可以看出调用的是com.netflix.eureka.registry.AbstractInstanceRegistry中345行的renew()方法，
/** * Marks the given instance of the given app name as renewed, and also marks whether it originated from * replication. * * @see com.netflix.eureka.lease.LeaseManager#renew(java.lang.String, java.lang.String, boolean) */ public boolean renew(String appName, String id, boolean isReplication) { RENEW.increment(isReplication); Map<String, Lease<InstanceInfo>> gMap = registry.get(appName); Lease<InstanceInfo> leaseToRenew = null; if (gMap != null) { leaseToRenew = gMap.get(id); } if (leaseToRenew == null) { RENEW_NOT_FOUND.increment(isReplication); logger.warn("DS: Registry: lease doesn\'t exist, registering resource: {} - {}", appName, id); return false; } else { InstanceInfo instanceInfo = leaseToRenew.getHolder(); if (instanceInfo != null) { // touchASGCache(instanceInfo.getASGName()); InstanceStatus overriddenInstanceStatus = this.getOverriddenInstanceStatus( instanceInfo, leaseToRenew, isReplication); if (overriddenInstanceStatus == InstanceStatus.UNKNOWN) { logger.info("Instance status UNKNOWN possibly due to deleted override for instance {}" + "; re-register required", instanceInfo.getId()); RENEW_NOT_FOUND.increment(isReplication); return false; } if (!instanceInfo.getStatus().equals(overriddenInstanceStatus)) { Object[] args = { instanceInfo.getStatus().name(), instanceInfo.getOverriddenStatus().name(), instanceInfo.getId() }; logger.info( "The instance status {} is different from overridden instance status {} for instance {}. " + "Hence setting the status to overridden status", args); instanceInfo.setStatus(overriddenInstanceStatus); } } renewsLastMin.increment(); leaseToRenew.renew(); return true; } }
其中 leaseToRenew.renew()是调用com.netflix.eureka.lease.Lease中的62行的renew()方法
public void renew() { lastUpdateTimestamp = System.currentTimeMillis() + duration; }
replicateToPeers(Action.Heartbeat, appName, id, null, null, isReplication);
调用自身的replicateToPeers()方法，在com.netflix.eureka.registry.PeerAwareInstanceRegistryImpl中的618行，主要接口实现方式和register基本一致：首先更新自身Eureka Server中服务的状态，再同步到其它Eureka Server中。
private void replicateToPeers(Action action, String appName, String id, InstanceInfo info /* optional */, InstanceStatus newStatus /* optional */, boolean isReplication) { Stopwatch tracer = action.getTimer().start(); try { if (isReplication) { numberOfReplicationsLastMin.increment(); } // If it is a replication already, do not replicate again as this will create a poison replication if (peerEurekaNodes == Collections.EMPTY_LIST || isReplication) { return; } // 同步把续约信息同步到其它的Eureka Server中 for (final PeerEurekaNode node : peerEurekaNodes.getPeerEurekaNodes()) { // If the url represents this host, do not replicate to yourself. if (peerEurekaNodes.isThisMyUrl(node.getServiceUrl())) { continue; } //根据action做相应操作的同步 replicateInstanceActionsToPeers(action, appName, id, info, newStatus, node); } } finally { tracer.stop(); } }