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();
        }
 }