Nacos源码解读04——服务发现

Nacos服务发现的方式

1.客户端获取
1.1:先是故障转移机制判断是否去本地文件中读取信息，读到则返回
1.2:再去本地服务列表读取信息(本地缓存)，没读到则创建一个空的服务，然后立刻去nacos中读取更新
1.3:读到了就返回，同时开启定时更新，定时向服务端同步信息 （正常1s，异常最多60s一次）
2.服务端通过GRPC推送
建立长连接、当服务发现变更的时候往订阅了服务的客户端推送事件

SpringBoot自动注入

项目启动的时候会通过自动注入的机制将
NacosDiscoveryClientConfiguration注入
当注入NacosDiscoveryClientConfiguration的时候会将DiscoveryClient一起注入Bean
DiscoveryClient实现了SpringCloud的DiscoveryClient接口，重点是getInstances和getServices方法，而且都是由NacosServiceDiscovery实现

获取实例信息

NacosDiscoveryClient

	private NacosServiceDiscovery serviceDiscovery;public NacosDiscoveryClient(NacosServiceDiscovery nacosServiceDiscovery) {this.serviceDiscovery = nacosServiceDiscovery;}@Overridepublic List<ServiceInstance> getInstances(String serviceId) {try {return serviceDiscovery.getInstances(serviceId);}catch (Exception e) {throw new RuntimeException("Can not get hosts from nacos server. serviceId: " + serviceId, e);}}

	public List<ServiceInstance> getInstances(String serviceId) throws NacosException {String group = discoveryProperties.getGroup();List<Instance> instances = namingService().selectInstances(serviceId, group,true);return hostToServiceInstanceList(instances, serviceId);}

NacosServiceDiscovery

	public List<ServiceInstance> getInstances(String serviceId) throws NacosException {//获取分组String group = discoveryProperties.getGroup();//查询服务下的实例List<Instance> instances = namingService().selectInstances(serviceId, group,true);//填充返回的实例信息数据return hostToServiceInstanceList(instances, serviceId);}

    @Overridepublic List<Instance> selectInstances(String serviceName, String groupName, boolean healthy) throws NacosException {return selectInstances(serviceName, groupName, healthy, true);}

    @Overridepublic List<Instance> selectInstances(String serviceName, String groupName, boolean healthy, boolean subscribe)throws NacosException {return selectInstances(serviceName, groupName, new ArrayList<String>(), healthy, subscribe);}

    @Overridepublic List<Instance> selectInstances(String serviceName, String groupName, List<String> clusters, boolean healthy,boolean subscribe) throws NacosException {ServiceInfo serviceInfo;String clusterString = StringUtils.join(clusters, ",");// 默认是订阅的if (subscribe) {//从缓存中获取实例信息serviceInfo = serviceInfoHolder.getServiceInfo(serviceName, groupName, clusterString);//如果获取不到则从服务端拉取if (null == serviceInfo) {serviceInfo = clientProxy.subscribe(serviceName, groupName, clusterString);}} else {// 如果未订阅服务信息，则直接从服务器进行查询serviceInfo = clientProxy.queryInstancesOfService(serviceName, groupName, clusterString, 0, false);}//获取服务中的实例信息return selectInstances(serviceInfo, healthy);}

从缓存中拿数据

    public ServiceInfo getServiceInfo(final String serviceName, final String groupName, final String clusters) {NAMING_LOGGER.debug("failover-mode: {}", failoverReactor.isFailoverSwitch());String groupedServiceName = NamingUtils.getGroupedName(serviceName, groupName);String key = ServiceInfo.getKey(groupedServiceName, clusters);if (failoverReactor.isFailoverSwitch()) {return failoverReactor.getService(key);}return serviceInfoMap.get(key);}

获取服务的实例信息

    private List<Instance> selectInstances(ServiceInfo serviceInfo, boolean healthy) {List<Instance> list;if (serviceInfo == null || CollectionUtils.isEmpty(list = serviceInfo.getHosts())) {return new ArrayList<Instance>();}Iterator<Instance> iterator = list.iterator();while (iterator.hasNext()) {Instance instance = iterator.next();// 保留 健康、启用、权重大于0 的实例if (healthy != instance.isHealthy() || !instance.isEnabled() || instance.getWeight() <= 0) {iterator.remove();}}return list;}

GRPC请求拉取服务实例信息

    @Overridepublic ServiceInfo subscribe(String serviceName, String groupName, String clusters) throws NacosException {NAMING_LOGGER.info("[SUBSCRIBE-SERVICE] service:{}, group:{}, clusters:{} ", serviceName, groupName, clusters);String serviceNameWithGroup = NamingUtils.getGroupedName(serviceName, groupName);String serviceKey = ServiceInfo.getKey(serviceNameWithGroup, clusters);//定时同步服务端serviceInfoserviceInfoUpdateService.scheduleUpdateIfAbsent(serviceName, groupName, clusters);//获取ServiceInfo 信息ServiceInfo result = serviceInfoHolder.getServiceInfoMap().get(serviceKey);//如果没有则从服务端拿if (null == result || !isSubscribed(serviceName, groupName, clusters)) {//GRPC请求result = grpcClientProxy.subscribe(serviceName, groupName, clusters);}//填充进Map中 这里可以看服务注册最后那部分代码最后也是调用serviceInfoHolder保存的serviceInfoHolder.processServiceInfo(result);return result;}

定时同步服务端ServiceInfo

    public void scheduleUpdateIfAbsent(String serviceName, String groupName, String clusters) {String serviceKey = ServiceInfo.getKey(NamingUtils.getGroupedName(serviceName, groupName), clusters);if (futureMap.get(serviceKey) != null) {return;}synchronized (futureMap) {if (futureMap.get(serviceKey) != null) {return;}//构建任务放到ScheduledFuture执行ScheduledFuture<?> future = addTask(new UpdateTask(serviceName, groupName, clusters));futureMap.put(serviceKey, future);}}

缓存订阅信息

    public void cacheSubscriberForRedo(String serviceName, String groupName, String cluster) {//拿服务当keyString key = ServiceInfo.getKey(NamingUtils.getGroupedName(serviceName, groupName), cluster);//构建需要缓存的订阅信息SubscriberRedoData redoData = SubscriberRedoData.build(serviceName, groupName, cluster);//缓存订阅信息synchronized (subscribes) {subscribes.put(key, redoData);}}

执行订阅

    public ServiceInfo doSubscribe(String serviceName, String groupName, String clusters) throws NacosException {//构建订阅请求SubscribeServiceRequest request = new SubscribeServiceRequest(namespaceId, groupName, serviceName, clusters,true);//执行订阅SubscribeServiceResponse response = requestToServer(request, SubscribeServiceResponse.class);//设置已订阅redoService.subscriberRegistered(serviceName, groupName, clusters);return response.getServiceInfo();}

设置订阅信息已订阅

    public void subscriberRegistered(String serviceName, String groupName, String cluster) {String key = ServiceInfo.getKey(NamingUtils.getGroupedName(serviceName, groupName), cluster);synchronized (subscribes) {SubscriberRedoData redoData = subscribes.get(key);// 标记订阅数据已订阅if (null != redoData) {redoData.setRegistered(true);}}}

Nacos订阅机制

Nacos的订阅机制，如果用一句话来描述就是：Nacos客户端通过一个定时任务，每6秒从注册中心获取实例列表，当发现实例发生变化时，发布变更事件，订阅者进行业务处理。该更新实例的更新实例，该更新本地缓存的更新本地缓存。
UpdateTask

 public class UpdateTask implements Runnable {public void run() {long delayTime = DEFAULT_DELAY;try {//校验订阅任务是否不对 如果不对就不处理 if (!changeNotifier.isSubscribed(groupName, serviceName, clusters) && !futureMap.containsKey(serviceKey)) {NAMING_LOGGER.info("update task is stopped, service:{}, clusters:{}", groupedServiceName, clusters);isCancel = true;return;}//从缓存中拿 Service信息ServiceInfo serviceObj = serviceInfoHolder.getServiceInfoMap().get(serviceKey);//如果拿不到则去服务端拉取if (serviceObj == null) {serviceObj = namingClientProxy.queryInstancesOfService(serviceName, groupName, clusters, 0, false);              //然后再填充进缓存 serviceInfoHolder.processServiceInfo(serviceObj);//更新下事件lastRefTime = serviceObj.getLastRefTime();return;}// 过期服务（服务的最新更新时间小于等于缓存刷新时间），从注册中心重新查询if (serviceObj.getLastRefTime() <= lastRefTime) {//服务过期了重新查serviceObj = namingClientProxy.queryInstancesOfService(serviceName, groupName, clusters, 0, false);             //在缓存进去serviceInfoHolder.processServiceInfo(serviceObj);}// 刷新更新时间lastRefTime = serviceObj.getLastRefTime();if (CollectionUtils.isEmpty(serviceObj.getHosts())) {incFailCount();return;}// 下次更新缓存时间设置，默认为6秒// TODO multiple time can be configured.delayTime = serviceObj.getCacheMillis() * DEFAULT_UPDATE_CACHE_TIME_MULTIPLE;// 重置失败数量为0resetFailCount();} catch (Throwable e) {incFailCount();NAMING_LOGGER.warn("[NA] failed to update serviceName: {}", groupedServiceName, e);} finally {// 下次调度刷新时间，下次执行的时间与failCount有关// failCount=0，则下次调度时间为6秒，最长为1分钟// 即当无异常情况下缓存实例的刷新时间是6秒if (!isCancel) {executor.schedule(this, Math.min(delayTime << failCount, DEFAULT_DELAY * 60),TimeUnit.MILLISECONDS);}}}}

实例变更事件处理

监听事件的注册

在NacosNamingService的subscribe方法中，通过如下方式进行了监听事件的注册：

    @Overridepublic void subscribe(String serviceName, String groupName, List<String> clusters, EventListener listener)throws NacosException {if (null == listener) {return;}String clusterString = StringUtils.join(clusters, ",");changeNotifier.registerListener(groupName, serviceName, clusterString, listener);clientProxy.subscribe(serviceName, groupName, clusterString);}

这里的changeNotifier.registerListener便是进行具体的事件注册逻辑

   public void registerListener(String groupName, String serviceName, String clusters, EventListener listener) {String key = ServiceInfo.getKey(NamingUtils.getGroupedName(serviceName, groupName), clusters);ConcurrentHashSet<EventListener> eventListeners = listenerMap.get(key);//这里用到了双重检查锁机制if (eventListeners == null) {synchronized (lock) {eventListeners = listenerMap.get(key);if (eventListeners == null) {eventListeners = new ConcurrentHashSet<EventListener>();listenerMap.put(key, eventListeners);}}}eventListeners.add(listener);}

可以看出，事件的注册便是将EventListener存储在InstancesChangeNotifier的listenerMap属性当中了。

这里的数据结构为Map，key为服务实例信息的拼接，value为监听事件的集合。

监听服务变更事件

因为UpdateTask 中假如没有从缓存中拿到服务信息则会通过grpc协议从服务端拉取然后会执行serviceInfoHolder.processServiceInfo方法缓存服务信息，当实例发生变化的话这个方法最终会发送一个InstancesChangeEvent 事件 所以这里会监听InstancesChangeEvent 事件进行处理

InstancesChangeNotifier

public class InstancesChangeNotifier extends Subscriber<InstancesChangeEvent> {private final Map<String, ConcurrentHashSet<EventListener>> listenerMap = new ConcurrentHashMap<String, ConcurrentHashSet<EventListener>>();@Overridepublic void onEvent(InstancesChangeEvent event) {String key = ServiceInfo.getKey(NamingUtils.getGroupedName(event.getServiceName(), event.getGroupName()), event.getClusters());ConcurrentHashSet<EventListener> eventListeners = listenerMap.get(key);if (CollectionUtils.isEmpty(eventListeners)) {return;}for (final EventListener listener : eventListeners) {//[] final com.alibaba.nacos.api.naming.listener.Event namingEvent = transferToNamingEvent(event);final com.alibaba.nacos.api.naming.listener.Event namingEvent = new NamingEvent(instancesChangeEvent.getServiceName(), instancesChangeEvent.getGroupName(),instancesChangeEvent.getClusters(), instancesChangeEvent.getHosts());// 最终调度执行listener.onEvent(namingEvent)，只在NacosWatch#start找到了有效的EventListener，见下文if (listener instanceof AbstractEventListener && ((AbstractEventListener) listener).getExecutor() != null) {((AbstractEventListener) listener).getExecutor().execute(() -> listener.onEvent(namingEvent));} else {listener.onEvent(namingEvent);}}}
}
}

public class NacosWatch implements ApplicationEventPublisherAware, SmartLifecycle, DisposableBean {private Map<String, EventListener> listenerMap = new ConcurrentHashMap(16);private final AtomicBoolean running = new AtomicBoolean(false);public void start() {if (this.running.compareAndSet(false, true)) {EventListener eventListener = (EventListener)this.listenerMap.computeIfAbsent(this.buildKey(), (event) -> {return new EventListener() {public void onEvent(Event event) {if (event instanceof NamingEvent) {List instances = ((NamingEvent)event).getInstances();//[] Optional instanceOptional = NacosWatch.this.selectCurrentInstance(instances);// 按IP和端口选择第一个instance作为当前的instanceOptional instanceOptional = instances.stream().filter((instance) -> {return this.properties.getIp().equals(instance.getIp()) && this.properties.getPort() == instance.getPort();}).findFirst()instanceOptional.ifPresent((currentInstance) -> {//[] NacosWatch.this.resetIfNeeded(currentInstance);// 重新设置properties的metadataif (!this.properties.getMetadata().equals(instance.getMetadata())) {this.properties.setMetadata(instance.getMetadata());}});}}};});}}

获取服务信息

NacosDiscoveryClient

	@Overridepublic List<String> getServices() {try {return serviceDiscovery.getServices();}catch (Exception e) {log.error("get service name from nacos server fail,", e);return Collections.emptyList();}}

	public List<String> getServices() throws NacosException {//获取分组String group = discoveryProperties.getGroup();//获取服务信息ListView<String> services = namingService().getServicesOfServer(1,Integer.MAX_VALUE, group);return services.getData();}

    @Overridepublic ListView<String> getServicesOfServer(int pageNo, int pageSize, String groupName) throws NacosException {return getServicesOfServer(pageNo, pageSize, groupName, null);}

    @Overridepublic ListView<String> getServicesOfServer(int pageNo, int pageSize, String groupName, AbstractSelector selector)throws NacosException {return clientProxy.getServiceList(pageNo, pageSize, groupName, selector);}

GRPC拉取信息

    @Overridepublic ListView<String> getServiceList(int pageNo, int pageSize, String groupName, AbstractSelector selector)throws NacosException {//构建请求ServiceListRequest request = new ServiceListRequest(namespaceId, groupName, pageNo, pageSize);if (selector != null) {if (SelectorType.valueOf(selector.getType()) == SelectorType.label) {request.setSelector(JacksonUtils.toJson(selector));}}//采用GRPC协议拉取信息ServiceListResponse response = requestToServer(request, ServiceListResponse.class);ListView<String> result = new ListView<String>();result.setCount(response.getCount());result.setData(response.getServiceNames());return result;}

服务端处理GRPC请求

接收获取服务的请求

ServiceListRequestHandler

    @Override@Secured(action = ActionTypes.READ)public ServiceListResponse handle(ServiceListRequest request, RequestMeta meta) throws NacosException {//根据命名空间获取这个命名空间下的所有服务信息  erviceManager.getInstance().getSingletons这个方法服务注册的时候里有Collection<Service> serviceSet = ServiceManager.getInstance().getSingletons(request.getNamespace());//构建返回信息ServiceListResponse result = ServiceListResponse.buildSuccessResponse(0, new LinkedList<>());//服务信息不等于空填充返回信息if (!serviceSet.isEmpty()) {Collection<String> serviceNameSet = selectServiceWithGroupName(serviceSet, request.getGroupName());// TODO select service by selectorList<String> serviceNameList = ServiceUtil.pageServiceName(request.getPageNo(), request.getPageSize(), serviceNameSet);result.setCount(serviceNameSet.size());result.setServiceNames(serviceNameList);}return result;}

订阅服务请求

SubscribeServiceRequestHandler

    @Override@Secured(action = ActionTypes.READ)public SubscribeServiceResponse handle(SubscribeServiceRequest request, RequestMeta meta) throws NacosException {//命名空间String namespaceId = request.getNamespace();//服务名称String serviceName = request.getServiceName();//分组名称String groupName = request.getGroupName();String app = request.getHeader("app", "unknown");String groupedServiceName = NamingUtils.getGroupedName(serviceName, groupName);//构建服务信息Service service = Service.newService(namespaceId, groupName, serviceName, true);//组装订阅请求Subscriber subscriber = new Subscriber(meta.getClientIp(), meta.getClientVersion(), app, meta.getClientIp(),namespaceId, groupedServiceName, 0, request.getClusters());//获取健康的实例       ServiceInfo serviceInfo = ServiceUtil.selectInstancesWithHealthyProtection(serviceStorage.getData(service),               //服务元数据信息    metadataManager.getServiceMetadata(service).orElse(null), subscriber);//是否订阅      if (request.isSubscribe()) {clientOperationService.subscribeService(service, subscriber, meta.getConnectionId());} else {clientOperationService.unsubscribeService(service, subscriber, meta.getConnectionId());}//构建返回数据return new SubscribeServiceResponse(ResponseCode.SUCCESS.getCode(), "success", serviceInfo);}

发送订阅事件 后续事件监听可参考服务事件处理的那篇文章

    @Overridepublic void subscribeService(Service service, Subscriber subscriber, String clientId) {Service singleton = ServiceManager.getInstance().getSingletonIfExist(service).orElse(service);Client client = clientManager.getClient(clientId);if (!clientIsLegal(client, clientId)) {return;}client.addServiceSubscriber(singleton, subscriber);client.setLastUpdatedTime();NotifyCenter.publishEvent(new ClientOperationEvent.ClientSubscribeServiceEvent(singleton, clientId));}

发送取消订阅事件 后续事件监听可参考服务事件处理的那篇文章

    @Overridepublic void unsubscribeService(Service service, Subscriber subscriber, String clientId) {Service singleton = ServiceManager.getInstance().getSingletonIfExist(service).orElse(service);Client client = clientManager.getClient(clientId);if (!clientIsLegal(client, clientId)) {return;}client.removeServiceSubscriber(singleton);client.setLastUpdatedTime();NotifyCenter.publishEvent(new ClientOperationEvent.ClientUnsubscribeServiceEvent(singleton, clientId));}

服务查询请求

ServiceQueryRequestHandler

    @Override@Secured(action = ActionTypes.READ)public QueryServiceResponse handle(ServiceQueryRequest request, RequestMeta meta) throws NacosException {//获取命名空间String namespaceId = request.getNamespace();//分组明String groupName = request.getGroupName();//服务名String serviceName = request.getServiceName();//创建服务信息Service service = Service.newService(namespaceId, groupName, serviceName);//集群String cluster = null == request.getCluster() ? "" : request.getCluster();boolean healthyOnly = request.isHealthyOnly();//获取服务信息ServiceInfo result = serviceStorage.getData(service);//获取服务元数据信息ServiceMetadata serviceMetadata = metadataManager.getServiceMetadata(service).orElse(null);// 获取有保护机制的健康实例result = ServiceUtil.selectInstancesWithHealthyProtection(result, serviceMetadata, cluster, healthyOnly, true,meta.getClientIp());//构建返回信息return QueryServiceResponse.buildSuccessResponse(result);}

    public ServiceInfo getData(Service service) {return serviceDataIndexes.containsKey(service) ? serviceDataIndexes.get(service) : getPushData(service);}

    public Optional<ServiceMetadata> getServiceMetadata(Service service) {return Optional.ofNullable(serviceMetadataMap.get(service));}