Eureka 续约 (心跳检测)

Eureka 续约 (心跳检测)

心跳，eureka client每隔一定的时间，会给eureka server发送心跳，保持心跳，让eureka server知道自己还活着，lease renewal，续约，心跳.

Eureka-Client 向 Eureka-Server 发起注册应用实例成功后获得租约 ( Lease )。
Eureka-Client 固定间隔向 Eureka-Server 发起续租( renew )，避免租约过期。

默认情况下，租约有效期为 90 秒，续租频率为 30 秒。两者比例为 1 : 3 ，保证在网络异常等情况下，有三次重试的机会。

(1)DiscoveryClient初始化的时候，会去调度一堆定时任务，其中有一个就是HeartbeatThread，心跳线程

(2)在这里可以看到，默认是每隔30秒去发送一次心跳，每隔30秒执行一次HeartbeatTHread线程的逻辑，发送心跳

(3)这边的话就是去发送这个心跳，走的是EurekaHttpClient的sendHeartbeat()方法，http://localhost:8080/v2/apps/ServiceA/i-000000-1，走的是put请求

/*** The heartbeat task that renews the lease in the given intervals.*/private class HeartbeatThread implements Runnable {public void run() {if (renew()) {lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis();}}}/*** Renew with the eureka service by making the appropriate REST call*/boolean renew() {EurekaHttpResponse<InstanceInfo> httpResponse;try {httpResponse = eurekaTransport.registrationClient.sendHeartBeat(instanceInfo.getAppName(), instanceInfo.getId(), instanceInfo, null);logger.debug(PREFIX + "{} - Heartbeat status: {}", appPathIdentifier, httpResponse.getStatusCode());if (httpResponse.getStatusCode() == Status.NOT_FOUND.getStatusCode()) {REREGISTER_COUNTER.increment();logger.info(PREFIX + "{} - Re-registering apps/{}", appPathIdentifier, instanceInfo.getAppName());long timestamp = instanceInfo.setIsDirtyWithTime();boolean success = register();if (success) {instanceInfo.unsetIsDirty(timestamp);}return success;}return httpResponse.getStatusCode() == Status.OK.getStatusCode();} catch (Throwable e) {logger.error(PREFIX + "{} - was unable to send heartbeat!", appPathIdentifier, e);return false;}}

(4)负责承接服务实例的心跳相关的这些操作的，是ApplicationsResource，服务相关的controller。找到ApplicationResource，再次找到InstanceResource，通过PUT请求，可以找到renewLease方法。

@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);// Not found in the registry, immediately ask for a registerif (!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 valueResponse response;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 winsif (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;}

(5)通过注册表的renew()方法，进去完成服务续约，实际进入AbstractInstanceRegistry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)) {logger.info("The instance status {} is different from overridden instance status {} for instance {}. "+ "Hence setting the status to overridden status", instanceInfo.getStatus().name(),overriddenInstanceStatus.name(),instanceInfo.getId());instanceInfo.setStatusWithoutDirty(overriddenInstanceStatus);}}// 新增 续租每分钟次数renewsLastMin.increment();// 设置 租约最后更新时间(续租)leaseToRenew.renew();return true;}}

实际的服务续约的逻辑，其实就是在Lease对象中，更新一下lastUpdateTimestamp这个时间戳，每次续约，就更新一下,duration这里加了一遍，也是eureka的bug，但是官网并不做修改。

public void renew() {lastUpdateTimestamp = System.currentTimeMillis() + duration;
}