nacos服务注册与发现原理解析
前言：nacos 玩过微服务的想必不会陌生，它是阿里对于springcloud孵化出来的产品，用来完成服务之间的注册发现和配置中心，其核心作用我就不废话了，提前去github下载好nacos的源码包和启动nacos server
大致流程：每个服务都会有一个nacos client，它用来和nacos server打交道 用来具体的服务注册 查询等操作，服务提供者在启动的时候会向nacos server注册自己，服务消费者在启动的时候订阅nacos server上的服务提供者
服务注册
首先需要引入spring-cloud-starter-alibaba-nacos-discovery包，本文的引入的版本是2.2.1
<dependency>
<groupId>com.alibaba.cloud</groupId>
<artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
<version>2.2.1.RELEASE</version>
</dependency>
根据sprin.factories配置来完成相关类的自动注册
我们重点来看这几个类，看名称可猜到是用来服务注册的，NacosServiceRegistryAutoConfiguration用来注册管理这几个bean
NacosServiceRegistry：完成服务注册，实现ServiceRegistry
NacosRegistration：用来注册时存储nacos服务端的相关信息
NacosAutoServiceRegistration 继承spring中的AbstractAutoServiceRegistration，AbstractAutoServiceRegistration继承ApplicationListener<WebServerInitializedEvent>，通过事件监听来发起服务注册，到时候会调用NacosServiceRegistry.register(registration)
来看具体如何注册
/******************************************************NacosServiceRegistry******************************************************/ public void register(Registration registration) { if (StringUtils.isEmpty(registration.getServiceId())) { log.warn("No service to register for nacos client..."); } else { String serviceId = registration.getServiceId(); String group = this.nacosDiscoveryProperties.getGroup(); Instance instance = this.getNacosInstanceFromRegistration(registration); try { this.namingService.registerInstance(serviceId, group, instance); } } } /******************************************************NacosNamingService******************************************************/ public void registerInstance(String serviceName, String groupName, Instance instance) throws NacosException { if (instance.isEphemeral()) { // 添加心跳检测 beatReactor.addBeatInfo(NamingUtils.getGroupedName(serviceName, groupName), beatInfo); } // 完成服务注册 serverProxy.registerService(NamingUtils.getGroupedName(serviceName, groupName), groupName, instance); } /******************************************************NacosNamingService******************************************************/ public void addBeatInfo(String serviceName, BeatInfo beatInfo) { String key = buildKey(serviceName, beatInfo.getIp(), beatInfo.getPort()); // 发起一个心跳检测任务 executorService.schedule(new BeatTask(beatInfo), beatInfo.getPeriod(), TimeUnit.MILLISECONDS); MetricsMonitor.getDom2BeatSizeMonitor().set(dom2Beat.size()); } /******************************************************BeatTask******************************************************/ class BeatTask implements Runnable { @Override public void run() { if (beatInfo.isStopped()) { return; } long nextTime = beatInfo.getPeriod(); try { // 向nacos服务发起心跳检测 JSONObject result = serverProxy.sendBeat(beatInfo, BeatReactor.this.lightBeatEnabled); long interval = result.getIntValue("clientBeatInterval"); boolean lightBeatEnabled = false; if (result.containsKey(CommonParams.LIGHT_BEAT_ENABLED)) { lightBeatEnabled = result.getBooleanValue(CommonParams.LIGHT_BEAT_ENABLED); } BeatReactor.this.lightBeatEnabled = lightBeatEnabled; if (interval > 0) { nextTime = interval; } int code = NamingResponseCode.OK; if (result.containsKey(CommonParams.CODE)) { code = result.getIntValue(CommonParams.CODE); } if (code == NamingResponseCode.RESOURCE_NOT_FOUND) { // 未注册 先完成注册 try { serverProxy.registerService(beatInfo.getServiceName(), NamingUtils.getGroupName(beatInfo.getServiceName()), instance); } } } // 发起下一次心跳检测 executorService.schedule(new BeatTask(beatInfo), nextTime, TimeUnit.MILLISECONDS); } }
服务提供者向nacos server发起服务注册前，先向nacos server建立起心跳检测机制，nacos server那边也有一个心跳检测，服务提供者不停的向nacos server发起心跳检测 告知自己的健康状态，nacos serve发现该服务心跳检测时间超时会发布超时事件来告知服务消费者
服务发现
服务发现由NacosWatch完成，它实现了Spring的Lifecycle接口，容器启动和销毁时会调用对应的start（）和stop（）方法
来看对应源码
@Override public void start() { // cas设置运行状态为true if (this.running.compareAndSet(false, true)) { // 延时执行一个服务发现任务 this.watchFuture = this.taskScheduler.scheduleWithFixedDelay( this::nacosServicesWatch, this.properties.getWatchDelay()); } } @Override public void stop() { // 设置运行状态为false 然后取消正在执行的任务 if (this.running.compareAndSet(true, false) && this.watchFuture != null) { this.watchFuture.cancel(true); } } public void nacosServicesWatch() { try { boolean changed = false; NamingService namingService = properties.namingServiceInstance(); // 获取nacos server上最新的服务提供者们 ListView<String> listView = properties.namingServiceInstance() .getServicesOfServer(1, Integer.MAX_VALUE); List<String> serviceList = listView.getData(); // 有新的订阅产生 订阅完后发布事件 Set<String> currentServices = new HashSet<>(serviceList); currentServices.removeAll(cacheServices); if (currentServices.size() > 0) { changed = true; } // 取消已经下线的服务订阅，发起取消订阅操作并删除订阅监听 if (cacheServices.removeAll(new HashSet<>(serviceList)) && cacheServices.size() > 0) { changed = true; for (String serviceName : cacheServices) { namingService.unsubscribe(serviceName, subscribeListeners.get(serviceName)); subscribeListeners.remove(serviceName); } } cacheServices = new HashSet<>(serviceList); // 订阅服务 并对每个服务都添加一个心跳检测监听 for (String serviceName : cacheServices) { if (!subscribeListeners.containsKey(serviceName)) { EventListener eventListener = event -> NacosWatch.this.publisher .publishEvent(new HeartbeatEvent(NacosWatch.this, nacosWatchIndex.getAndIncrement())); subscribeListeners.put(serviceName, eventListener); namingService.subscribe(serviceName, eventListener); } } // 有服务变化 发布事件 if (changed) { this.publisher.publishEvent( new HeartbeatEvent(this, nacosWatchIndex.getAndIncrement())); } } catch (Exception e) { log.error("Error watching Nacos Service change", e); } }
大致流程：nacos client这边在spring容器启动后执行一个服务订阅操作的延时任务，这个任务执行时先拉取nacos server那边最新的服务列表，然后与本地缓存的服务列表进行比较，取消订阅下线的服务，然后向nacos server发起订阅操作，订阅所有服务
那么服务消费者如何实时感知服务提供者的状态信息呢
1、服务消费者订阅后会执行一个轮询任务（每1s执行一次）用来拉取最新的服务提供者信息并实时更新,实现在HostReactor中的UpdateTask完成，下面来看代码
public class UpdateTask implements Runnable { long lastRefTime = Long.MAX_VALUE; private String clusters; private String serviceName; public UpdateTask(String serviceName, String clusters) { this.serviceName = serviceName; this.clusters = clusters; } @Override public void run() { try { // 拿到当前的服务信息 ServiceInfo serviceObj = serviceInfoMap.get(ServiceInfo.getKey(serviceName, clusters)); // 为空 拉取最新的服务列表随后更新 if (serviceObj == null) { updateServiceNow(serviceName, clusters); // 继续轮询 executor.schedule(this, DEFAULT_DELAY, TimeUnit.MILLISECONDS); return; } if (serviceObj.getLastRefTime() <= lastRefTime) { // 当前服务未及时更新 进行更新操作 updateServiceNow(serviceName, clusters); serviceObj = serviceInfoMap.get(ServiceInfo.getKey(serviceName, clusters)); } else { // if serviceName already updated by push, we should not override it // since the push data may be different from pull through force push refreshOnly(serviceName, clusters); } // 设置服务最新的更新时间 lastRefTime = serviceObj.getLastRefTime(); // 订阅被取消 if (!eventDispatcher.isSubscribed(serviceName, clusters) && !futureMap.containsKey(ServiceInfo.getKey(serviceName, clusters))) { // abort the update task: NAMING_LOGGER.info("update task is stopped, service:" + serviceName + ", clusters:" + clusters); return; } // 继续下一次轮询 executor.schedule(this, serviceObj.getCacheMillis(), TimeUnit.MILLISECONDS); } catch (Throwable e) { NAMING_LOGGER.warn("[NA] failed to update serviceName: " + serviceName, e); } } }
2、上面服务注册时我们说过，服务提供者注册时nacos服务端也有一个相应的心跳检测，当心跳检测超时也就是未及时收到服务提供者的心跳包，nacos server判定该服务状态异常 随后通过UDP推送服务信息用来告知对应服务消费者，服务消费者通过PushReceiver来处理udp协议，HostReactor.processServiceJson(String json)来更新本地服务列表
/********************************PushReceiver*****************************/ public void run() { while (true) { try { // byte[] is initialized with 0 full filled by default byte[] buffer = new byte[UDP_MSS]; DatagramPacket packet = new DatagramPacket(buffer, buffer.length); udpSocket.receive(packet); String json = new String(IoUtils.tryDecompress(packet.getData()), "UTF-8").trim(); NAMING_LOGGER.info("received push data: " + json + " from " + packet.getAddress().toString()); PushPacket pushPacket = JSON.parseObject(json, PushPacket.class); String ack; if ("dom".equals(pushPacket.type) || "service".equals(pushPacket.type)) { // 处理变更信息 hostReactor.processServiceJSON(pushPacket.data); // send ack to server ack = "{\"type\": \"push-ack\"" + ", \"lastRefTime\":\"" + pushPacket.lastRefTime + "\", \"data\":" + "\"\"}"; } else if ("dump".equals(pushPacket.type)) { // dump data to server ack = "{\"type\": \"dump-ack\"" + ", \"lastRefTime\": \"" + pushPacket.lastRefTime + "\", \"data\":" + "\"" + StringUtils.escapeJavaScript(JSON.toJSONString(hostReactor.getServiceInfoMap())) + "\"}"; } else { // do nothing send ack only ack = "{\"type\": \"unknown-ack\"" + ", \"lastRefTime\":\"" + pushPacket.lastRefTime + "\", \"data\":" + "\"\"}"; } udpSocket.send(new DatagramPacket(ack.getBytes(Charset.forName("UTF-8")), ack.getBytes(Charset.forName("UTF-8")).length, packet.getSocketAddress())); } catch (Exception e) { NAMING_LOGGER.error("[NA] error while receiving push data", e); } } }
服务注册和订阅我只讲解了主要流程，nacos server那边处理源码太多就不一一贴出来了，根据对应的api接口进去一看便知，nacos源码比较好理解，没有什么特别难读懂的地方，这边只是提供给大家一个看源码的思路，具体详细流程还需要读者自己去细读
下面通过代码来模拟nacos服务注册和订阅
先启动一个nacos server，然后打开控制台，添加一个命名空间
服务注册:分别注册两个服务，其中一个服务有两个实例
public class ServerRegister { public static void main(String[] args) throws Exception { Properties properties = new Properties(); properties.setProperty("serverAddr", "http://localhost:8848"); properties.setProperty("namespace", "c7981cfd-ccb8-4a9f-8e80-cd1f9633ecec"); NamingService namingService = NacosFactory.createNamingService(properties); // 同一个服务注册两个实例 namingService.registerInstance("serverProvider_1", "127.0.0.1", 8080); namingService.registerInstance("serverProvider_1", "127.0.0.1", 8081); namingService.registerInstance("serverProvider_2", "127.0.0.1", 7070);
// 获取服务名为serverProvider_1的实例信息 List<Instance> serverProvider = namingService.getAllInstances("serverProvider_1"); System.out.println(JSONArray.toJSONString(serverProvider, SerializerFeature.PrettyFormat, SerializerFeature.WriteMapNullValue, SerializerFeature.WriteDateUseDateFormat)); System.in.read(); } }
服务订阅：获取所有的服务提供者，然后进行订阅 并添加一个事件用来监听订阅成功后的实例
public class ServerCustomer { public static void main(String[] args) throws Exception { Properties properties = new Properties(); properties.setProperty("serverAddr", "http://localhost:8848"); properties.setProperty("namespace", "c7981cfd-ccb8-4a9f-8e80-cd1f9633ecec"); NamingService namingService = NacosFactory.createNamingService(properties); List<String> serverList = namingService.getServicesOfServer(1, Integer.MAX_VALUE).getData(); System.out.println("得到服务提供者列表:" + JSONArray.toJSONString(serverList)); for (String server : serverList) { // 订阅serverProvider服务 并添加一个监听器用来监听服务状态 namingService.subscribe(server, event -> { NamingEvent namingEvent = (NamingEvent) event; System.out.println(JSONObject.toJSONString(namingEvent, SerializerFeature.PrettyFormat, SerializerFeature.WriteMapNullValue, SerializerFeature.WriteDateUseDateFormat)); }); } System.in.read(); } }
打印信息：
nacos控制台也能看到相应服务信息
随后把服务提供者下线 再来看服务消费者那边的输出，可以看到服务实例已全部下线
nacos控制台
