心跳机制与服务健康检查设计原理及源码剖析

   客户端会调用/nacos/v1/ns/instance/beat接口进行心跳，主要逻辑有：

   1.如果在Nacos Server没有找到相对应的Instance，那么就构造一个Instance，源码如下：

    // com.alibaba.nacos.naming.controllers.InstanceController#beat@CanDistro@PutMapping("/beat")@Secured(parser = NamingResourceParser.class, action = ActionTypes.WRITE)public ObjectNode beat(HttpServletRequest request) throws Exception {// 省略其它代码。。。。。。。// 获取InstanceInstance instance = serviceManager.getInstance(namespaceId, serviceName, clusterName, ip, port);// 如果Instance为null，那么就构造一个Instance进行注册if (instance == null) {if (clientBeat == null) {result.put(CommonParams.CODE, NamingResponseCode.RESOURCE_NOT_FOUND);return result;}Loggers.SRV_LOG.warn("[CLIENT-BEAT] The instance has been removed for health mechanism, "+ "perform data compensation operations, beat: {}, serviceName: {}", clientBeat, serviceName);instance = new Instance();instance.setPort(clientBeat.getPort());instance.setIp(clientBeat.getIp());instance.setWeight(clientBeat.getWeight());instance.setMetadata(clientBeat.getMetadata());instance.setClusterName(clusterName);instance.setServiceName(serviceName);instance.setInstanceId(instance.getInstanceId());instance.setEphemeral(clientBeat.isEphemeral());// 把Client注册到NacosserviceManager.registerInstance(namespaceId, serviceName, instance);}Service service = serviceManager.getService(namespaceId, serviceName);// 省略其它代码。。。。。。。// 处理Client端的心跳service.processClientBeat(clientBeat);// 省略其它代码。。。。。。。return result;
}

2.如果在Nacos Server中有当前实例，那么就更新一下lastBeat、healthy等，源码如下：

// com.alibaba.nacos.naming.healthcheck.ClientBeatProcessor#run
@Override
public void run() {// 省略其它代码。。。。。。。for (Instance instance : instances) {// 从Service中找到需要更新的Instanceif (instance.getIp().equals(ip) && instance.getPort() == port) {if (Loggers.EVT_LOG.isDebugEnabled()) {Loggers.EVT_LOG.debug("[CLIENT-BEAT] refresh beat: {}", rsInfo.toString());}// 把当前时间设置到Insance的lastBeat中instance.setLastBeat(System.currentTimeMillis());if (!instance.isMarked()) {if (!instance.isHealthy()) {// 更新一下健康状态instance.setHealthy(true);Loggers.EVT_LOG.info("service: {} {POS} {IP-ENABLED} valid: {}:{}@{}, region: {}, msg: client beat ok",cluster.getService().getName(), ip, port, cluster.getName(),UtilsAndCommons.LOCALHOST_SITE);getPushService().serviceChanged(service);}}}}
}

    服务端也会启动线程去检测客户端心跳信息，来判断客户端是否存活，Nacos是怎么启动心跳检测的，怎么心跳检测的？

    请看源码：

// com.alibaba.nacos.naming.core.Service#init
// 在注册Instance的时候会调用这个方法
public void init() {// HealthCheckReactor.scheduleCheck(clientBeatCheckTask);for (Map.Entry<String, Cluster> entry : clusterMap.entrySet()) {entry.getValue().setService(this);entry.getValue().init();}
}
// com.alibaba.nacos.naming.healthcheck.HealthCheckReactor#scheduleCheck
public static void scheduleCheck(ClientBeatCheckTask task) {// 这里会启动一个定时任务来检测心跳，按照的是固定频率5s// 其实这里最后采用的JDK的scheduleWithFixedDelayfutureMap.computeIfAbsent(task.taskKey(),k -> GlobalExecutor.scheduleNamingHealth(task, 5000, 5000, TimeUnit.MILLISECONDS));
}// com.alibaba.nacos.naming.healthcheck.ClientBeatCheckTask#run
@Override
public void run() {try {// 判断是否是当前Nacos实例来启动心跳检测if (!getDistroMapper().responsible(service.getName())) {return;}if (!getSwitchDomain().isHealthCheckEnabled()) {return;}List<Instance> instances = service.allIPs(true);// first set health status of instances:// 检测实例的健康状态for (Instance instance : instances) {// 判断心跳是否超时，默认超时时间为15秒if (System.currentTimeMillis() - instance.getLastBeat() > instance.getInstanceHeartBeatTimeOut()) {if (!instance.isMarked()) {if (instance.isHealthy()) {// 如果心跳超时，首先把此服务的健康状态设置为falseinstance.setHealthy(false);Loggers.EVT_LOG.info("{POS} {IP-DISABLED} valid: {}:{}@{}@{}, region: {}, msg: client timeout after {}, last beat: {}",instance.getIp(), instance.getPort(), instance.getClusterName(),service.getName(), UtilsAndCommons.LOCALHOST_SITE,instance.getInstanceHeartBeatTimeOut(), instance.getLastBeat());// 发布一个服务变更事件getPushService().serviceChanged(service);// 发布一个心跳超时事件ApplicationUtils.publishEvent(new InstanceHeartbeatTimeoutEvent(this, instance));}}}}if (!getGlobalConfig().isExpireInstance()) {return;}// then remove obsolete instances:// 删除过时的实例（默认30s）for (Instance instance : instances) {if (instance.isMarked()) {continue;}if (System.currentTimeMillis() - instance.getLastBeat() > instance.getIpDeleteTimeout()) {// delete instanceLoggers.SRV_LOG.info("[AUTO-DELETE-IP] service: {}, ip: {}", service.getName(),JacksonUtils.toJson(instance));deleteIp(instance);}}} catch (Exception e) {Loggers.SRV_LOG.warn("Exception while processing client beat time out.", e);}}

    默认的心跳超时时间为15s，如果发现Instance中的lastBeat的时间与当前时间对比，小于当前时间15s以上那么就判断Instance为不健康的状态，首先会设置Instance中的healthy为false，然后发布一个服务变更事件，再发布一个心跳超时事件。