在分布式服务中,原来的单体服务会被拆分成一个个微服务,服务注册实例到注册中心,服务消费者通过注册中心获取实例列表,直接请求调用服务。服务是如何注册到注册中心,服务如果挂了,服务是如何检测?带着这些问题,我们从源码上对服务注册进行简单的源码分析。版本 2.1.1Nacos Server:2.1.1spring-cloud-starter-alibaba:2.1.1.RELEASEspring-boot:2.1.1.RELEASE方便统一版本,客户端和服务端版本号都为2.1.1。客户端启动nacos服务注册和发现需要添加maven依赖:<dependency> <groupId>com.alibaba.cloud</groupId> <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId> <version>${latest.version}</version></dependency>根据maven依赖找到对应的spring.factories文件:在spring.factories文件里找到启动配置类信息,SpringBoot服务启动时会将这些配置类信息注入到bean容器中。org.springframework.boot.autoconfigure.EnableAutoConfiguration=\ com.alibaba.cloud.nacos.NacosDiscoveryAutoConfiguration,\ com.alibaba.cloud.nacos.ribbon.RibbonNacosAutoConfiguration,\ com.alibaba.cloud.nacos.endpoint.NacosDiscoveryEndpointAutoConfiguration,\ com.alibaba.cloud.nacos.discovery.NacosDiscoveryClientAutoConfiguration,\ com.alibaba.cloud.nacos.discovery.configclient.NacosConfigServerAutoConfigurationorg.springframework.cloud.bootstrap.BootstrapConfiguration=\ com.alibaba.cloud.nacos.discovery.configclient.NacosDiscoveryClientConfigServiceBootstrapConfiguration服务注册的核心配置类为:NacosDiscoveryAutoConfiguration,该类配置三个bean对象:NacosServiceRegistryNacosRegistrationNacosAutoServiceRegistrationNacosAutoServiceRegistrationNacosAutoServiceRegistration继承了抽象类AbstractAutoServiceRegistration。AbstractAutoServiceRegistration抽象类又实现了ApplicationListener接口。实现ApplicationListener接口的方法,会在Spring容器初始化完成之后调用onApplicationEvent方法:public void onApplicationEvent(WebServerInitializedEvent event) { bind(event);}调用bind方法:public void bind(WebServerInitializedEvent event) { ApplicationContext context = event.getApplicationContext(); if (context instanceof ConfigurableWebServerApplicationContext) { if ("management".equals(((ConfigurableWebServerApplicationContext) context) .getServerNamespace())) { return; } } this.port.compareAndSet(0, event.getWebServer().getPort()); // 调用 start 方法 this.start(); }调用了start方法:public void start() { if (!isEnabled()) { if (logger.isDebugEnabled()) { logger.debug("Discovery Lifecycle disabled. Not starting"); } return; } if (!this.running.get()) { this.context.publishEvent( new InstancePreRegisteredEvent(this, getRegistration())); register(); if (shouldRegisterManagement()) { registerManagement(); } this.context.publishEvent( new InstanceRegisteredEvent<>(this, getConfiguration())); this.running.compareAndSet(false, true); }}调用了register方法,最终调用的是NacosServiceRegistry类的register方法。NacosServiceRegistry根据上文可知,服务器启动后调用NacosServiceRegistry类的register方法,该方法实现将实例注册到服务端:public void register(Registration registration) { if (StringUtils.isEmpty(registration.getServiceId())) { log.warn("No service to register for nacos client..."); return; } String serviceId = registration.getServiceId(); String group = nacosDiscoveryProperties.getGroup(); // 创建实例 Instance instance = getNacosInstanceFromRegistration(registration); try { // 注册实例 namingService.registerInstance(serviceId, group, instance); log.info("nacos registry, {} {} {}:{} register finished", group, serviceId, instance.getIp(), instance.getPort()); } catch (Exception e) { log.error("nacos registry, {} register failed...{},", serviceId, registration.toString(), e); }}创建实例,然后通过namingService.registerInstance方法注册实例,然后查看registerInstance方法:@Override(992988)public void registerInstance(String serviceName, String groupName, Instance instance) throws NacosException { if (instance.isEphemeral()) { // 封装心跳包 BeatInfo beatInfo = new BeatInfo(); beatInfo.setServiceName(NamingUtils.getGroupedName(serviceName, groupName)); beatInfo.setIp(instance.getIp()); beatInfo.setPort(instance.getPort()); beatInfo.setCluster(instance.getClusterName()); beatInfo.setWeight(instance.getWeight()); beatInfo.setMetadata(instance.getMetadata()); beatInfo.setScheduled(false); long instanceInterval = instance.getInstanceHeartBeatInterval(); beatInfo.setPeriod(instanceInterval == 0 ? DEFAULT_HEART_BEAT_INTERVAL : instanceInterval); // 发送心跳包 beatReactor.addBeatInfo(NamingUtils.getGroupedName(serviceName, groupName), beatInfo); } // 发送实例 serverProxy.registerService(NamingUtils.getGroupedName(serviceName, groupName), groupName, instance);}registerInstance主要做两件事:发送心跳包beatReactor.addBeatInfo使用定时服务,每隔5s向服务端发送一次心跳请求,通过http请求发送心跳信息,路径为/v1/ns/instance/beat。心跳请求定时任务使用线程池ScheduledThreadPoolExecutor.schedule(),而该方法只会调用一次,定时任务的实现是在每次请求任务只会再调用一次ScheduledThreadPoolExecutor.schedule(),简单说就是nacos在发送心跳的时候,会调用schedule方法,在schedule要执行的任务中,如果正常发送完心跳,会再次调用schedule方法。那为什么不直接调用周期执行的线程池ScheduledThreadPoolExecutor.scheduleAtFixedRate()?可能是由于发送心跳服务发生异常后,定时任务还会继续执行,但是周期执行的线程池遇到报错后也不会重复调用执行的任务。线程任务BeatTask的run方法,,每次执行会先判断isStopped,如果是false,说明心跳停止,就不会触发下次执行任务。如果使用定时任务scheduleAtFixedRate,即使心跳停止还会继续执行任务,造成资源不必要浪费。注册实例registerService主要封装实例信息,比如ip、port、servicename,将这些信息通过http请求发送给服务端。路径为/v1/ns/instance。根据上面流程,查看以下的流程图:服务端服务端就是注册中心,服务注册到注册中心,在https://github.com/alibaba/nacos/releases/tag/2.1.1下载源码部署到本地,方便调式和查看,部署方式详见我的另外一篇文章Nacos 源码环境搭建。服务端主要接收两个信息:心跳包和实例信息。心跳包客户端向服务请求的路径为/v1/ns/instance/beat,对应的服务端为InstanceController类的beat方法:@PutMapping("/beat")@Secured(action = ActionTypes.WRITE)public ObjectNode beat(HttpServletRequest request) throws Exception { ObjectNode result = JacksonUtils.createEmptyJsonNode(); result.put(SwitchEntry.CLIENT_BEAT_INTERVAL, switchDomain.getClientBeatInterval()); String beat = WebUtils.optional(request, "beat", StringUtils.EMPTY); RsInfo clientBeat = null; // 判断是否有心跳,存在心跳就转成RsInfo if (StringUtils.isNotBlank(beat)) { clientBeat = JacksonUtils.toObj(beat, RsInfo.class); } String clusterName = WebUtils .optional(request, CommonParams.CLUSTER_NAME, UtilsAndCommons.DEFAULT_CLUSTER_NAME); String ip = WebUtils.optional(request, "ip", StringUtils.EMPTY); int port = Integer.parseInt(WebUtils.optional(request, "port", "0")); if (clientBeat != null) { if (StringUtils.isNotBlank(clientBeat.getCluster())) { clusterName = clientBeat.getCluster(); } else { // fix #2533 clientBeat.setCluster(clusterName); } ip = clientBeat.getIp(); port = clientBeat.getPort(); } String namespaceId = WebUtils.optional(request, CommonParams.NAMESPACE_ID, Constants.DEFAULT_NAMESPACE_ID); String serviceName = WebUtils.required(request, CommonParams.SERVICE_NAME); NamingUtils.checkServiceNameFormat(serviceName); Loggers.SRV_LOG.debug("[CLIENT-BEAT] full arguments: beat: {}, serviceName: {}, namespaceId: {}", clientBeat, serviceName, namespaceId); // 获取实例信息 BeatInfoInstanceBuilder builder = BeatInfoInstanceBuilder.newBuilder(); builder.setRequest(request); int resultCode = getInstanceOperator() .handleBeat(namespaceId, serviceName, ip, port, clusterName, clientBeat, builder); result.put(CommonParams.CODE, resultCode); // 下次发送心跳包间隔 result.put(SwitchEntry.CLIENT_BEAT_INTERVAL, getInstanceOperator().getHeartBeatInterval(namespaceId, serviceName, ip, port, clusterName)); result.put(SwitchEntry.LIGHT_BEAT_ENABLED, switchDomain.isLightBeatEnabled()); return result;}在handleBeat方法中执行线程任务ClientBeatProcessorV2的run方法,延长lastHeartBeatTime时间。注册中心会定时查询实例,当前时间 - lastHeartBeatTime > 设置时间(默认15秒),就标记实例为不健康实例。如果心跳实例不健康,发送通知给订阅方,变更实例。服务端在15秒没有收到心跳包会将实例设置为不健康,在30秒没有收到心跳包会将临时实例移除掉。实例注册客户端请求的地址是/nacos/v1/ns/instance, 对应的是服务端是在InstanceController类。找到类上对应的post请求方法上。注册流程:InstanceController#register ——>InstanceOperatorClientImpl#registerInstance ——>ClientOperationServiceProxy#registerInstance ——>EphemeralClientOperationServiceImpl#registerInstance创建 Service服务注册后,将服务存储在一个双层map集合中:private final Map<String, Map<String, Service>> serviceMap = new ConcurrentHashMap<>();通过是否存在ephemeral,true,走AP模式,否则走CP模式。Nacos 默认就是采用的AP模式使用Distro协议实现。实现的接口是EphemeralConsistencyService对节点信息的持久化主要是调用put方法,会先写入到DataStore中:public void onPut(String key, Record value) { if (KeyBuilder.matchEphemeralInstanceListKey(key)) { Datum<Instances> datum = new Datum<>(); datum.value = (Instances) value; datum.key = key; datum.timestamp.incrementAndGet(); // 数据持久化到缓存中 dataStore.put(key, datum); } if (!listeners.containsKey(key)) { return; } notifier.addTask(key, DataOperation.CHANGE);}总结从依赖上找到需要启动的是要加载的服务注册类NacosDiscoveryAutoConfiguration,主要配置三个对象NacosServiceRegistryNacosRegistrationNacosAutoServiceRegistrationNacosServiceRegistry类的register方法,封装实例和心跳信息通过http请求,定时发送发送心跳包,默认时间间隔是5秒。通过http请求,发送实例信息。服务端接收到心跳请求,更新心跳包最新时间。服务端在15秒没有收到心跳包会将实例设为不健康,在30秒没有收到心跳包会将临时实例移除掉。接收到服务注册接口,通过ephemeral判断是否走AP还是走CP,AP模式使用Distro协议。通过调用EphemeralConsistencyService接口实现,持久化实例信息。参考Nacos源码之注册中心的实现Nacos 服务注册源码分析