// new DiscoveryClient 的时候初始化心跳定时任务周期性的调度// Heartbeat timerscheduler.schedule(    new TimedSupervisorTask(        "heartbeat",        scheduler,        heartbeatExecutor,        // 续约周期是 30s.也就是每 30s 执行一次        renewalIntervalInSecs,        TimeUnit.SECONDS,        expBackOffBound,        new HeartbeatThread()    ),    renewalIntervalInSecs, TimeUnit.SECONDS);
private class HeartbeatThread implements Runnable {    public void run() {        if (renew()) {            lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis();        }    }}

boolean renew() {    EurekaHttpResponse httpResponse;    try {        // 1、通过jerseyclient 去发送心中请求        httpResponse = eurekaTransport.registrationClient.sendHeartBeat(instanceInfo.getAppName(), instanceInfo.getId(), instanceInfo, null);        logger.debug("{} - Heartbeat status: {}", PREFIX + appPathIdentifier, httpResponse.getStatusCode());        // 2、如果 404 的话去发起 register 请求        if (httpResponse.getStatusCode() == 404) {            REREGISTER_COUNTER.increment();// 这里是一个计数器，如果失败 + 1            logger.info("{} - Re-registering apps/{}", PREFIX + appPathIdentifier, instanceInfo.getAppName());            long timestamp = instanceInfo.setIsDirtyWithTime();            boolean success = register();            if (success) {                instanceInfo.unsetIsDirty(timestamp);            }            return success;        }        // 3、成功返回 200,续约成功         return httpResponse.getStatusCode() == 200;    } catch (Throwable e) {        logger.error("{} - was unable to send heartbeat!", PREFIX + appPathIdentifier, e);        return false;    }}

@PUTpublic 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);    boolean isSuccess = registry.renew(app.getName(), id, isFromReplicaNode);
    // 如果注册表中没发现直接返回 404,那 client 发现 404 后就会执行 registry 逻辑去 addInstance(新增实例) 添加到 registry(注册表) 中去    // Not found in the registry, immediately ask for a register    if (!isSuccess) {        logger.warn("Not Found (Renew): {} - {}", app.getName(), id);        return Response.status(Status.NOT_FOUND).build();    }    // Check if we need to sync based on dirty time stamp, the client instance might have changed some value    Response response = null;    if (lastDirtyTimestamp != null && serverConfig.shouldSyncWhenTimestampDiffers()) {        response = this.validateDirtyTimestamp(Long.valueOf(lastDirtyTimestamp), isFromReplicaNode);        // Store the overridden status since the validation found out the node that replicates wins        if (response.getStatus() == Response.Status.NOT_FOUND.getStatusCode()                && (overriddenStatus != null)                && !(InstanceStatus.UNKNOWN.name().equals(overriddenStatus))                && isFromReplicaNode) {            registry.storeOverriddenStatusIfRequired(app.getAppName(), id, InstanceStatus.valueOf(overriddenStatus));        }    } else {        response = Response.ok().build();    }    logger.debug("Found (Renew): {} - {}; reply status={}" + app.getName(), id, response.getStatus());    return response;}

// super.renew() 主要是调用 AbstractInstanceRegistry 的 renew 方法public boolean renew(final String appName, final String id, final boolean isReplication) {    if (super.renew(appName, id, isReplication)) {        //这个就是复制到其他 eureka 服务节点         replicateToPeers(Action.Heartbeat, appName, id, null, null, isReplication);        return true;    }    return false;}

public boolean renew(String appName, String id, boolean isReplication) {    // 1、统计信息新增 1     RENEW.increment(isReplication);    // 2、从 registry(注册表)中获取信息 appName 为 key 的 Map 信息    Map<String, Lease> gMap = registry.get(appName);    Lease leaseToRenew = null;    // 3、苑 Lease 信息    if (gMap != null) {        leaseToRenew = gMap.get(id);    }    // 4、如果为空则直接返回 404,客户端会发起 registry 请求(前面的文章看到过这样的逻辑处理)    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) {           // 4.1、InstanceStatus 判断，如果为 UNKNOWN，可能被删除覆盖了，所以可能客户端需要重新注册            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;            }            // 4.2、如果两者不一样，则更新 status            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.setStatusWithoutDirty(overriddenInstanceStatus);            }        }        // 5、统计信息新增(上一分钟的续约次数)        renewsLastMin.increment();        // 6、更新 lastUpdateTimestamp        leaseToRenew.renew();        return true;    }}

private void replicateInstanceActionsToPeers(Action action, String appName,                                             String id, InstanceInfo info, InstanceStatus newStatus,                                             PeerEurekaNode node) {    try {        InstanceInfo infoFromRegistry = null;        CurrentRequestVersion.set(Version.V2);        switch (action) {            case Cancel:                node.cancel(appName, id);                break;            case Heartbeat:                // 这里我们可以知道会调用到这里来                // 从 overriddenInstanceStatusMap 中获取 InstanceStatus，默认是 1 个小时后过期。                InstanceStatus overriddenStatus = overriddenInstanceStatusMap.get(id);                // 这个方法说一下                infoFromRegistry = getInstanceByAppAndId(appName, id, false);                node.heartbeat(appName, id, infoFromRegistry, overriddenStatus, false);                break;            case Register:                node.register(info);                break;            case StatusUpdate:                infoFromRegistry = getInstanceByAppAndId(appName, id, false);                node.statusUpdate(appName, id, newStatus, infoFromRegistry);                break;            case DeleteStatusOverride:                infoFromRegistry = getInstanceByAppAndId(appName, id, false);                node.deleteStatusOverride(appName, id, infoFromRegistry);                break;        }    } catch (Throwable t) {        logger.error("Cannot replicate information to {} for action {}", node.getServiceUrl(), action.name(), t);    }}
@Overridepublic InstanceInfo getInstanceByAppAndId(String appName, String id, boolean includeRemoteRegions) {    // 1、从注册表中获取 appName 为 key 的 Map     Map> leaseMap = registry.get(appName);    Lease lease = null;    if (leaseMap != null) {        lease = leaseMap.get(id);    }    // 2、判断 Lease 如果不为空，且(Lease 开启没有开启或者 lease 没有过期)则返回装饰的 InstanceInfo    if (lease != null        && (!isLeaseExpirationEnabled() || !lease.isExpired())) {        return decorateInstanceInfo(lease);    } else if (includeRemoteRegions) {        for (RemoteRegionRegistry remoteRegistry : this.regionNameVSRemoteRegistry.values()) {            Application application = remoteRegistry.getApplication(appName);            if (application != null) {                return application.getByInstanceId(id);            }        }    }    return null;}
 @Overridepublic boolean isLeaseExpirationEnabled() {    // 1、这个是判断自我保护模式是否开启(这个模式是默认开启的，后面EurekaServer 自我保护源码分析的时候会分析一下，怎么来判断等等)    if (!isSelfPreservationModeEnabled()) {        // The self preservation mode is disabled, hence allowing the instances to expire.        //如果自我保护没有开启，说明此时是可以过期的，所以返回 true。        // 因为如果自我保护开启，就不会进来，说明此时要判断一下心跳来判断是否 lease过期开启        return true;    }    //2、阈值 > 0,且上一分钟的心跳数 > 阈值才说明 lease 过期开启否则返回 false    return numberOfRenewsPerMinThreshold > 0 && getNumOfRenewsInLastMin() > numberOfRenewsPerMinThreshold;}

public void heartbeat(final String appName, final String id,                      final InstanceInfo info, final InstanceStatus overriddenStatus,                      boolean primeConnection) throws Throwable {    // 1、传递的是 false 不会进来    if (primeConnection) {        // We do not care about the result for priming request.        replicationClient.sendHeartBeat(appName, id, info, overriddenStatus);        return;    }    // 2、构造一个 ReplicationTask     ReplicationTask replicationTask = new InstanceReplicationTask(targetHost, Action.Heartbeat, info, overriddenStatus, false) {        @Override        public EurekaHttpResponseexecute() throws Throwable {            return replicationClient.sendHeartBeat(appName, id, info, overriddenStatus);        }
        @Override        public void handleFailure(int statusCode, Object responseEntity) throws Throwable {            super.handleFailure(statusCode, responseEntity);            if (statusCode == 404) {                logger.warn("{}: missing entry.", getTaskName());                if (info != null) {                    logger.warn("{}: cannot find instance id {} and hence replicating the instance with status {}",                            getTaskName(), info.getId(), info.getStatus());                    register(info);                }            } else if (config.shouldSyncWhenTimestampDiffers()) {                InstanceInfo peerInstanceInfo = (InstanceInfo) responseEntity;                if (peerInstanceInfo != null) {                    syncInstancesIfTimestampDiffers(appName, id, info, peerInstanceInfo);                }            }        }    };    // 3、获取 expiryTime    long expiryTime = System.currentTimeMillis() + getLeaseRenewalOf(info);    // 4、分发到 batchingDispatcher     batchingDispatcher.process(taskId("heartbeat", info), replicationTask, expiryTime);}