在前面两篇文章中，我和大家一起学习 Nacos 的基本概念， 以及就 Nacos 做为配置中心将配置持久化到 MySQL 中。本文我们一起来学习 Nacos 作为服务注册中心原理。

环境介绍：

• Jdk 1.8
• nacos-server-1.4.2
• spring-boot-2.3.5.RELEASE
• spring-cloud-Hoxton.SR8
• spring-cloiud-alibab-2.2.5.RELEASE

Nacos 服务架构

以 Spring-Boot 为服务基础搭建平台， Nacos 在服务架构中的位置如下图所示：

总的来说和 Nacos 功能类似的中间件有 Eureka、Zookeeper、Consul 、Etcd 等。Nacos 最大的特点就是既能够支持 AP、也能够支持 CP 模式，在分区一致性方面使用的是 Raft 协议来实现。

Nacos 客户端

我们以 spring-cloud-starter-alibaba-nacos-discovery 依赖为例

<dependency>
  <groupId>com.alibaba.cloud</groupId>
  <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
</dependency>

它是一个标准的 spring-cloud 插件，我们首先就可以看 spring.factories 这个文件，来找到它的启动配置类信息

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
  com.alibaba.cloud.nacos.discovery.NacosDiscoveryAutoConfiguration,\
  com.alibaba.cloud.nacos.ribbon.RibbonNacosAutoConfiguration,\
  com.alibaba.cloud.nacos.endpoint.NacosDiscoveryEndpointAutoConfiguration,\
  com.alibaba.cloud.nacos.registry.NacosServiceRegistryAutoConfiguration,\
  com.alibaba.cloud.nacos.discovery.NacosDiscoveryClientConfiguration,\
  com.alibaba.cloud.nacos.discovery.reactive.NacosReactiveDiscoveryClientConfiguration,\
  com.alibaba.cloud.nacos.discovery.configclient.NacosConfigServerAutoConfiguration,\
  com.alibaba.cloud.nacos.NacosServiceAutoConfiguration
org.springframework.cloud.bootstrap.BootstrapConfiguration=\
  com.alibaba.cloud.nacos.discovery.configclient.NacosDiscoveryClientConfigServiceBootstrapConfiguration

我们通常都是查看 “中间件名” + AutoConfiguration 开头的类， 由此我可以定位到 NacosDiscoveryAutoConfiguration 作为我们优先查看的类。

服务注册客户端

添加依赖

Nacos 服务注册是客户端主动发起，在 Spring 启动的过程中利用 Spring 提供的拓展方法来完成注册。首先我们需要导入spring-cloud-starter-alibaba-nacos-discovery依赖

<dependency>
  <groupId>com.alibaba.cloud</groupId>
  <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
</dependency>

分析源码

对于 spring-boot 组件我们首先先找它的 META-INF/spring.factories 文件

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
  com.alibaba.cloud.nacos.discovery.NacosDiscoveryAutoConfiguration,\
  com.alibaba.cloud.nacos.ribbon.RibbonNacosAutoConfiguration,\
  com.alibaba.cloud.nacos.endpoint.NacosDiscoveryEndpointAutoConfiguration,\
  com.alibaba.cloud.nacos.registry.NacosServiceRegistryAutoConfiguration,\
  com.alibaba.cloud.nacos.discovery.NacosDiscoveryClientConfiguration,\
  com.alibaba.cloud.nacos.discovery.reactive.NacosReactiveDiscoveryClientConfiguration,\
  com.alibaba.cloud.nacos.discovery.configclient.NacosConfigServerAutoConfiguration,\
  com.alibaba.cloud.nacos.NacosServiceAutoConfiguration
org.springframework.cloud.bootstrap.BootstrapConfiguration=\
  com.alibaba.cloud.nacos.discovery.configclient.NacosDiscoveryClientConfigServiceBootstrapConfiguration

通过我的分析发现 NacosServiceRegistryAutoConfiguration 是咱们服务注册的核心配置类，该类中定义了三个核心的 Bean 对象：

• NacosServiceRegistry
• NacosRegistration
• NacosAutoServiceRegistration

NacosAutoServiceRegistration

NacosAutoServiceRegistration 实现了服务向 Nacos 发起注册的功能，它继承自抽象类 AbstractAutoServiceRegistration 。

在抽象类 AbstractAutoServiceRegistration 中实现 ApplicationContextAware、ApplicationListener<WebServerInitializedEvent> 接口。在容器启动、并且上下文准备就绪过后会调用 onApplicationEvent 方法

public void onApplicationEvent(WebServerInitializedEvent event) {
   bind(event);
}

实际调用 bind(event) 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());
   this.start();
}

然后调用 start() 方法

public void start() {
	if (!isEnabled()) {
		if (logger.isDebugEnabled()) {
			logger.debug("Discovery Lifecycle disabled. Not starting");
		}
		return;
	}

	// only initialize if nonSecurePort is greater than 0 and it isn't already running
	// because of containerPortInitializer below
	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);
	}

}

最后调用 register(); 在内部去调用 serviceRegistry.register() 方法完成服务注册。

private final ServiceRegistry<R> serviceRegistry;

protected void register() {
   this.serviceRegistry.register(getRegistration());
}

NacosServiceRegistry

NacosServiceRegistry 类主要的目的就是

public void register(Registration registration) {

   if (StringUtils.isEmpty(registration.getServiceId())) {
      log.warn("No service to register for nacos client...");
      return;
   }
	 // 默认情况下，会通过反射返回一个 `com.alibaba.nacos.client.naming.NacosNamingService` 的实例
   NamingService namingService = namingService();
   // 获取 serviceId , 默认使用配置: spring.application.name 
   String serviceId = registration.getServiceId();
   // 获取 group , 默认 DEFAULT_GROUP 
   String group = nacosDiscoveryProperties.getGroup();

   // 创建 instance 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);
      // rethrow a RuntimeException if the registration is failed.
      // issue : https://github.com/alibaba/spring-cloud-alibaba/issues/1132
      rethrowRuntimeException(e);
   }
}

我们可以看到最后调用的是 namingService.registerInstance(serviceId, group, instance); 方法。

public void registerInstance(String serviceName, String groupName, Instance instance) throws NacosException {
    NamingUtils.checkInstanceIsLegal(instance);
    String groupedServiceName = NamingUtils.getGroupedName(serviceName, groupName);
    if (instance.isEphemeral()) {
        BeatInfo beatInfo = beatReactor.buildBeatInfo(groupedServiceName, instance);
        beatReactor.addBeatInfo(groupedServiceName, beatInfo);
    }
    serverProxy.registerService(groupedServiceName, groupName, instance);
}

然后再调用 serverProxy.registerService(groupedServiceName, groupName, instance); 方法进行服务注册，通过 beatReactor.addBeatinfo() 创建 schedule 每间隔 5s 向服务端发送一次心跳数据

public void registerService(String serviceName, String groupName, Instance instance) throws NacosException {
    
    NAMING_LOGGER.info("[REGISTER-SERVICE] {} registering service {} with instance: {}", namespaceId, serviceName,
            instance);
    
    final Map<String, String> params = new HashMap<String, String>(16);
    params.put(CommonParams.NAMESPACE_ID, namespaceId);
    params.put(CommonParams.SERVICE_NAME, serviceName);
    params.put(CommonParams.GROUP_NAME, groupName);
    params.put(CommonParams.CLUSTER_NAME, instance.getClusterName());
    params.put("ip", instance.getIp());
    params.put("port", String.valueOf(instance.getPort()));
    params.put("weight", String.valueOf(instance.getWeight()));
    params.put("enable", String.valueOf(instance.isEnabled()));
    params.put("healthy", String.valueOf(instance.isHealthy()));
    params.put("ephemeral", String.valueOf(instance.isEphemeral()));
    params.put("metadata", JacksonUtils.toJson(instance.getMetadata()));
    
    // POST: /nacos/v1/ns/instance 进行服务注册
    reqApi(UtilAndComs.nacosUrlInstance, params, HttpMethod.POST);
    
}

服务注册服务端

Nacos 做为服务注册中心，既可以实现AP ，也能实现 CP 架构。来维护我们服务中心的服务列表。下面是我们服务列表一个简单的数据模型示意图：

其实就和咱们 NacosServiceRegistry#registry 构建 Instance 实例的过程是一致的。继续回到我们源码分析我们直接来看服务端的 /nacos/v1/ns/instance 接口，被定义在 InstanceController#register 方法。

服务注册

在 InstanceController#register 方法中，主要是解析 request 参数然后调用 serviceManager.registerInstance , 如果返回 ok 就表示注册成功。

@CanDistro
@PostMapping
@Secured(parser = NamingResourceParser.class, action = ActionTypes.WRITE)
public String register(HttpServletRequest request) throws Exception {
    
    final String namespaceId = WebUtils
            .optional(request, CommonParams.NAMESPACE_ID, Constants.DEFAULT_NAMESPACE_ID);
    final String serviceName = WebUtils.required(request, CommonParams.SERVICE_NAME);
    NamingUtils.checkServiceNameFormat(serviceName);
    
    final Instance instance = parseInstance(request);
    
    serviceManager.registerInstance(namespaceId, serviceName, instance);
    return "ok";
}

registerInstance 方法的调用

public void registerInstance(String namespaceId, String serviceName, Instance instance) throws NacosException {
    
    createEmptyService(namespaceId, serviceName, instance.isEphemeral());
    
    Service service = getService(namespaceId, serviceName);
    
    if (service == null) {
        throw new NacosException(NacosException.INVALID_PARAM,
                "service not found, namespace: " + namespaceId + ", service: " + serviceName);
    }
    
    addInstance(namespaceId, serviceName, instance.isEphemeral(), instance);
}

再调用 addInstance() 方法

@Resource(name = "consistencyDelegate")
private ConsistencyService consistencyService;

public void addInstance(String namespaceId, String serviceName, boolean ephemeral, Instance... ips)
        throws NacosException {
    
    String key = KeyBuilder.buildInstanceListKey(namespaceId, serviceName, ephemeral);
    
    Service service = getService(namespaceId, serviceName);
    
    synchronized (service) {
        List<Instance> instanceList = addIpAddresses(service, ephemeral, ips);
        
        Instances instances = new Instances();
        instances.setInstanceList(instanceList);
        
        consistencyService.put(key, instances);
    }
}

调用 consistencyService.put(key, instances); 刷新 service 中的所有 instance。我们通过 consistencyService 的定义可以知道它将调用 DelegateConsistencyServiceImpl 类的 put 方法。在这个地方有一个 AP/CP 模式的选择我们可以通过

@Override
public void put(String key, Record value) throws NacosException {
    mapConsistencyService(key).put(key, value);
}

// AP 或者 CP 模式的选择， AP 模式采用 Distro 协议， CP 模式采用 Raft 协议。
private ConsistencyService mapConsistencyService(String key) {
    return KeyBuilder.matchEphemeralKey(key) ? ephemeralConsistencyService : persistentConsistencyService;
}

AP 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

@Override
public void put(String key, Record value) throws NacosException {
    // 数据持久化
    onPut(key, value);
    // 通知其他服务节点 
    distroProtocol.sync(new DistroKey(key, KeyBuilder.INSTANCE_LIST_KEY_PREFIX), DataOperation.CHANGE,
            globalConfig.getTaskDispatchPeriod() / 2);
}

在调用 doPut 来保存数据并且发通知

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 
        dataStore.put(key, datum);
    }
    
    if (!listeners.containsKey(key)) {
        return;
    }
    
    notifier.addTask(key, DataOperation.CHANGE);
}

在 notifier.addTask 主要是通过 tasks.offer(Pair.with(datumKey, action)); 向阻塞队列 tasks 中放注册实例信息。通过 Notifier#run 方法来进行异步操作以保证效率

public class Notifier implements Runnable {
    
    @Override
    public void run() {
        Loggers.DISTRO.info("distro notifier started");
        
        for (; ; ) {
            try {
                Pair<String, DataOperation> pair = tasks.take();
                handle(pair);
            } catch (Throwable e) {
                Loggers.DISTRO.error("[NACOS-DISTRO] Error while handling notifying task", e);
            }
        }
    }
    
    private void handle(Pair<String, DataOperation> pair) {
 				// 省略部分代码
            for (RecordListener listener : listeners.get(datumKey)) {
                count++;
                try {
                    if (action == DataOperation.CHANGE) {
                        listener.onChange(datumKey, dataStore.get(datumKey).value);
                        continue;
                    }
                    if (action == DataOperation.DELETE) {
                        listener.onDelete(datumKey);
                        continue;
                    }
                } catch (Throwable e) {
                    Loggers.DISTRO.error("[NACOS-DISTRO] error while notifying listener of key: {}", datumKey, e);
                }
            }
    }
}

如果是 DataOperation.CHANGE 类型的事件会调用 listener.onChange(datumKey, dataStore.get(datumKey).value); 其实我们的 listener 就是我们的 Service 对象。

public void onChange(String key, Instances value) throws Exception {
    
    Loggers.SRV_LOG.info("[NACOS-RAFT] datum is changed, key: {}, value: {}", key, value);
    
    for (Instance instance : value.getInstanceList()) {
        
        if (instance == null) {
            // Reject this abnormal instance list:
            throw new RuntimeException("got null instance " + key);
        }
        
        if (instance.getWeight() > 10000.0D) {
            instance.setWeight(10000.0D);
        }
        
        if (instance.getWeight() < 0.01D && instance.getWeight() > 0.0D) {
            instance.setWeight(0.01D);
        }
    }
    
    updateIPs(value.getInstanceList(), KeyBuilder.matchEphemeralInstanceListKey(key));
    
    recalculateChecksum();
}

updateIPs 方法会将服务实例信息，更新到注册表的内存中去，并且会以 udp 的方式通知当前服务的订阅者。

public void updateIPs(Collection<Instance> instances, boolean ephemeral) {
    Map<String, List<Instance>> ipMap = new HashMap<>(clusterMap.size());
    for (String clusterName : clusterMap.keySet()) {
        ipMap.put(clusterName, new ArrayList<>());
    }
    
    for (Instance instance : instances) {
        try {
            if (instance == null) {
                Loggers.SRV_LOG.error("[NACOS-DOM] received malformed ip: null");
                continue;
            }
            
            if (StringUtils.isEmpty(instance.getClusterName())) {
                instance.setClusterName(UtilsAndCommons.DEFAULT_CLUSTER_NAME);
            }
            
            if (!clusterMap.containsKey(instance.getClusterName())) {
                Loggers.SRV_LOG
                        .warn("cluster: {} not found, ip: {}, will create new cluster with default configuration.",
                                instance.getClusterName(), instance.toJson());
                Cluster cluster = new Cluster(instance.getClusterName(), this);
                cluster.init();
                getClusterMap().put(instance.getClusterName(), cluster);
            }
            
            List<Instance> clusterIPs = ipMap.get(instance.getClusterName());
            if (clusterIPs == null) {
                clusterIPs = new LinkedList<>();
                ipMap.put(instance.getClusterName(), clusterIPs);
            }
            
            clusterIPs.add(instance);
        } catch (Exception e) {
            Loggers.SRV_LOG.error("[NACOS-DOM] failed to process ip: " + instance, e);
        }
    }
    
    for (Map.Entry<String, List<Instance>> entry : ipMap.entrySet()) {
        //make every ip mine
        List<Instance> entryIPs = entry.getValue();
        // 更新服务列表
        clusterMap.get(entry.getKey()).updateIps(entryIPs, ephemeral);
    }
    
    setLastModifiedMillis(System.currentTimeMillis());
    // 推送服务订阅者消息 
    getPushService().serviceChanged(this);
    StringBuilder stringBuilder = new StringBuilder();
    
    for (Instance instance : allIPs()) {
        stringBuilder.append(instance.toIpAddr()).append("_").append(instance.isHealthy()).append(",");
    }
    
    Loggers.EVT_LOG.info("[IP-UPDATED] namespace: {}, service: {}, ips: {}", getNamespaceId(), getName(),
            stringBuilder.toString());
    
}

CP 模式

Nacos 默认就是采用的 CP 模式使用 Raft 协议实现。实现类是 PersistentConsistencyServiceDelegateImpl

首先我们先看他的 put 方法

public void put(String key, Record value) throws NacosException {
    checkIsStopWork();
    try {
        raftCore.signalPublish(key, value);
    } catch (Exception e) {
        Loggers.RAFT.error("Raft put failed.", e);
        throw new NacosException(NacosException.SERVER_ERROR, "Raft put failed, key:" + key + ", value:" + value,
                e);
    }
}

调用 raftCore.signalPublish(key, value); 主要的步骤如下

• 判断是否是 Leader 节点，如果不是 Leader 节点将请求转发给 Leader 节点处理；
• 如果是 Leader 节点，首先执行 onPublish(datum, peers.local()); 方法，内部首先通过 raftStore.updateTerm(local.term.get()); 方法持久化到文件，然后通过 NotifyCenter.publishEvent(ValueChangeEvent.builder().key(datum.key).action(DataOperation.CHANGE).build());异步更新到内存；
• 通过 CountDownLatch 实现了一个过半机制 new CountDownLatch(peers.majorityCount()) 只有当成功的节点大于 N/2 + 1 的时候才返回成功。
• 调用其他的 Nacos 节点的 /raft/datum/commit 同步实例信息。

public void signalPublish(String key, Record value) throws Exception {
    if (stopWork) {
        throw new IllegalStateException("old raft protocol already stop work");
    }
    if (!isLeader()) {
        ObjectNode params = JacksonUtils.createEmptyJsonNode();
        params.put("key", key);
        params.replace("value", JacksonUtils.transferToJsonNode(value));
        Map<String, String> parameters = new HashMap<>(1);
        parameters.put("key", key);
        
        final RaftPeer leader = getLeader();
        
        raftProxy.proxyPostLarge(leader.ip, API_PUB, params.toString(), parameters);
        return;
    }
    
    OPERATE_LOCK.lock();
    try {
        final long start = System.currentTimeMillis();
        final Datum datum = new Datum();
        datum.key = key;
        datum.value = value;
        if (getDatum(key) == null) {
            datum.timestamp.set(1L);
        } else {
            datum.timestamp.set(getDatum(key).timestamp.incrementAndGet());
        }
        
        ObjectNode json = JacksonUtils.createEmptyJsonNode();
        json.replace("datum", JacksonUtils.transferToJsonNode(datum));
        json.replace("source", JacksonUtils.transferToJsonNode(peers.local()));
        
        onPublish(datum, peers.local());
        
        final String content = json.toString();
        
        final CountDownLatch latch = new CountDownLatch(peers.majorityCount());
        for (final String server : peers.allServersIncludeMyself()) {
            if (isLeader(server)) {
                latch.countDown();
                continue;
            }
            final String url = buildUrl(server, API_ON_PUB);
            HttpClient.asyncHttpPostLarge(url, Arrays.asList("key", key), content, new Callback<String>() {
                @Override
                public void onReceive(RestResult<String> result) {
                    if (!result.ok()) {
                        Loggers.RAFT
                                .warn("[RAFT] failed to publish data to peer, datumId={}, peer={}, http code={}",
                                        datum.key, server, result.getCode());
                        return;
                    }
                    latch.countDown();
                }
                
                @Override
                public void onError(Throwable throwable) {
                    Loggers.RAFT.error("[RAFT] failed to publish data to peer", throwable);
                }
                
                @Override
                public void onCancel() {
                
                }
            });
            
        }
        
        if (!latch.await(UtilsAndCommons.RAFT_PUBLISH_TIMEOUT, TimeUnit.MILLISECONDS)) {
            // only majority servers return success can we consider this update success
            Loggers.RAFT.error("data publish failed, caused failed to notify majority, key={}", key);
            throw new IllegalStateException("data publish failed, caused failed to notify majority, key=" + key);
        }
        
        long end = System.currentTimeMillis();
        Loggers.RAFT.info("signalPublish cost {} ms, key: {}", (end - start), key);
    } finally {
        OPERATE_LOCK.unlock();
    }
}

判断 AP 模式还是 CP 模式

如果注册 nacos 的 client 节点注册时 ephemeral=true，那么 nacos 集群对这个 client 节点的效果就是 ap 的采用 distro，而注册nacos 的 client 节点注册时 ephemeral=false，那么nacos 集群对这个节点的效果就是 cp 的采用 raft。根据 client 注册时的属性，ap，cp 同时混合存在，只是对不同的 client 节点效果不同

Nacos 源码调试

Nacos 启动文件

首先我们需要找到 Nacos 的启动类，首先需要找到启动的 jar.

然后我们在解压 target/nacos-server.jar

解压命令：

# 解压 jar 包
tar -zxvf nacos-server.jar

# 查看 MANIFEST.MF 内容
cat META-INF/MANIFEST.MF

Manifest-Version: 1.0
Implementation-Title: nacos-console 1.4.2
Implementation-Version: 1.4.2
Archiver-Version: Plexus Archiver
Built-By: xiweng.yy
Spring-Boot-Layers-Index: BOOT-INF/layers.idx
Specification-Vendor: Alibaba Group
Specification-Title: nacos-console 1.4.2
Implementation-Vendor-Id: com.alibaba.nacos
Spring-Boot-Version: 2.5.0-RC1
Implementation-Vendor: Alibaba Group
Main-Class: org.springframework.boot.loader.PropertiesLauncher
Spring-Boot-Classpath-Index: BOOT-INF/classpath.idx
Start-Class: com.alibaba.nacos.Nacos
Spring-Boot-Classes: BOOT-INF/classes/
Spring-Boot-Lib: BOOT-INF/lib/
Created-By: Apache Maven 3.6.3
Build-Jdk: 1.8.0_231
Specification-Version: 1.4.2

通过 MANIFEST.MF 中的配置信息，我们可以找到 Start-Class 这个配置这个类就是 Spring-Boot 项目的启动类 com.alibaba.nacos.Nacos

Nacos 调试

通过 com.alibaba.nacos.Nacos 的启动类，我们可以通过这个类在 Idea 中进行启动，然后调试。

参考链接

nacos.io

github.com/alibaba/nac…