Nacos源码—3.Nacos集群高可用分析一

亢安芙 · 2025-6-2 23:08:44

大纲
1.Nacos集群的几个问题
2.单节点对服务进行心跳健康检查和同步检查结果
3.集群新增服务实例时如何同步给其他节点
4.集群节点的健康状态变动时的数据同步
5.集群新增节点时如何同步已有服务实例数据

1.Nacos集群的几个问题
问题一：在单机模式下，Nacos服务端会开启心跳健康检查的定时任务。那么在集群模式下，是否有必要让全部集群节点都执行这个定时任务？

问题二：Nacos服务端通过心跳健康检查的定时任务感知服务实例健康状态改变时，如何把服务实例的健康状态同步给其他Nacos集群节点？

问题三：一个新服务实例发起注册请求，只会有一个Nacos集群节点处理对应请求，那么处理完注册请求后，集群节点间应该如何同步服务实例数据？

问题四：假设Nacos集群有三个节点，现在需要新增了一个节点，那么新增的节点应该如何从集群中同步已存在的服务实例数据？

问题五：Nacos集群节点相互之间，是否有心跳机制来检测集群节点是否可用？

2.单节点对服务进行心跳健康检查和同步检查结果
(1)集群对服务进行心跳健康检查的设计
(2)选择一个节点对服务进行心跳健康检查的源码
(3)集群之间同步服务的健康状态的源码
(4)总结

(1)集群对服务进行心跳健康检查的架构设计
假设Nacos集群有三个节点：现已知单机模式下的Nacos服务端是会开启心跳健康检查的定时任务的。既然集群节点有三个，是否每个节点都要执行心跳健康检查的定时任务？

方案一：三个节点全都去执行心跳健康检查任务。如果每个节点执行的结果都不同，那么以哪个为准？

方案二：只有一个节点去执行心跳健康检查任务，然后把检查结果同步给其他节点。

明显方案二逻辑简洁清晰，而Nacos集群也选择了方案二。在Nacos集群模式下，三个节点都会开启一个心跳健康检查的定时任务，但只有一个节点会真正地执行心跳健康检查的逻辑。然后在检查完成后，会开启一个定时任务将检查结果同步给其他节点。

(2)选择一个节点对服务进行心跳健康检查的源码
对服务进行心跳健康检查的任务，其实就是ClientBeatCheckTask任务。Nacos服务端在处理服务实例注册接口请求时，就会开启这个任务。如下所示：

ClientBeatCheckTask这个类是一个线程任务。在ClientBeatCheckTask的run()方法中，一开始就有两个if判断。第一个if判断：判断当前节点在集群模式下是否需要对该Service执行心跳健康检查任务。第二个if判断：是否开启了健康检查任务，默认是开启的。注意：ClientBeatProcessor用于处理服务实例的心跳，服务实例和服务都需要心跳健康检查。

在集群模式下，为了保证只有一个节点对该Service执行心跳健康检查，就需要第一个if判断中的DistroMapper的responsible()方法来实现了。通过DistroMapper的responsible()方法可知：只会有一个集群节点能够对该Service执行心跳健康检查。而其他的集群节点，并不会去执行对该Service的心跳健康检查。

//Check and update statues of ephemeral instances, remove them if they have been expired.
public class ClientBeatCheckTask implements Runnable {
private Service service;//每个ClientBeatCheckTask都会对应一个Service
...
@JsonIgnore
public DistroMapper getDistroMapper() {
return ApplicationUtils.getBean(DistroMapper.class);
}
@Override
public void run() {
try {
//第一个if判断：DistroMapper.responsible()方法
//判断当前节点在集群模式下是否需要对该Service执行心跳健康检查任务
if (!getDistroMapper().responsible(service.getName())) {
return;
}
//第二个if判断：
//是否开启了健康检查任务，默认是开启的
if (!getSwitchDomain().isHealthCheckEnabled()) {
return;
}
List<Instance> instances = service.allIPs(true);
//first set health status of instances:
for (Instance instance : instances) {
if (System.currentTimeMillis() - instance.getLastBeat() > instance.getInstanceHeartBeatTimeOut()) {
if (!instance.isMarked()) {
if (instance.isHealthy()) {
instance.setHealthy(false);
getPushService().serviceChanged(service);
ApplicationUtils.publishEvent(new InstanceHeartbeatTimeoutEvent(this, instance));
}
}
}
}
if (!getGlobalConfig().isExpireInstance()) {
return;
}
//then remove obsolete instances:
for (Instance instance : instances) {
if (instance.isMarked()) {
continue;
}
if (System.currentTimeMillis() - instance.getLastBeat() > instance.getIpDeleteTimeout()) {
//delete instance
deleteIp(instance);
}
}
} catch (Exception e) {
Loggers.SRV_LOG.warn("Exception while processing client beat time out.", e);
}
}
...
}
//Distro mapper, judge which server response input service.
@Component("distroMapper")
public class DistroMapper extends MemberChangeListener {
//List of service nodes, you must ensure that the order of healthyList is the same for all nodes.
private volatile List<String> healthyList = new ArrayList<>();
//init server list.
@PostConstruct
public void init() {
NotifyCenter.registerSubscriber(this);//注册订阅者
this.healthyList = MemberUtil.simpleMembers(memberManager.allMembers());
}
...
//Judge whether current server is responsible for input service.
public boolean responsible(String serviceName) {
//获取集群节点数量，这里假设的是三个集群节点
final List<String> servers = healthyList;
//如果采用单机模式启动，直接返回true
if (!switchDomain.isDistroEnabled() || EnvUtil.getStandaloneMode()) {
return true;
}
//如果没有可用的健康集群节点，直接返回false
if (CollectionUtils.isEmpty(servers)) {
//means distro config is not ready yet
return false;
}
int index = servers.indexOf(EnvUtil.getLocalAddress());
int lastIndex = servers.lastIndexOf(EnvUtil.getLocalAddress());
if (lastIndex < 0 || index < 0) {
return true;
}
//对serviceName进行Hash操作，然后对servers.size()取模，得到负责执行心跳健康检查任务的那个节点索引
int target = distroHash(serviceName) % servers.size();
return target >= index && target <= lastIndex;
}
private int distroHash(String serviceName) {
return Math.abs(serviceName.hashCode() % Integer.MAX_VALUE);
}
...
}

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三.第一个异步任务ServiceReporter
首先从内存注册表中，获取全部的服务名称。ServiceManager的getAllServiceNames()方法返回的是一个Map对象。其中的key是对应的命名空间ID，value是对应命名空间下的全部服务名称。然后遍历allServiceNames中的内容，此时会有两个for循环来处理。最后这个任务执行完，会继续提交一个延时执行的任务进行健康检查。

第一个for循环：遍历某命名空间ID下的全部服务名称，封装请求参数。
首先采用同样的Hash算法，判断遍历到的Service是否需要同步健康结果。如果需要执行，则把参数放到ServiceChecksum对象中。然后通过JacksonUtils转成JSON数据后，再放到Message请求参数对象。

第二个for循环：遍历集群节点，发送请求给其他节点进行数据同步。
首先判断是否是自身节点，如果是则跳过。否则调用ServiceStatusSynchronizer的send()方法。通过向其他集群节点的接口发起请求，来实现心跳健康检查结果的同步。集群节点同步的核心方法就在ServiceStatusSynchronizer的send()方法中。

通过ServiceStatusSynchronizer的send()方法中的代码可知，最终会通过HTTP方式进行数据同步，请求地址是"v1/ns/service/status"。该请求地址对应的请求处理入口是ServiceController的serviceStatus()方法。

在ServiceController的serviceStatus()方法中，如果通过对比入参和注册表的ServiceChecksum后，发现服务状态发生了改变，那么就会调用ServiceManager.addUpdatedServiceToQueue()方法。

在addUpdatedServiceToQueue()方法中，首先会把传入的参数包装成ServiceKey对象，然后放入到toBeUpdatedServicesQueue阻塞队列中。

既然最后会将ServiceKey对象放入到阻塞队列中，那必然有一个异步任务，从阻塞队列中获取ServiceKey对象进行处理。这个处理逻辑和处理服务实例注册时，将Pair对象放入阻塞队列一样，而这个异步任务便是ServiceManager的init()方法的第二个异步任务。

//Core manager storing all services in Nacos.
@Component
public class ServiceManager implements RecordListener<Service> {
...
//Init service maneger.
@PostConstruct
public void init() {
//用来发起同步心跳健康检查结果请求的异步任务
GlobalExecutor.scheduleServiceReporter(new ServiceReporter(), 60000, TimeUnit.MILLISECONDS);
//用来处理同步心跳健康检查结果请求的异步任务：内存队列削峰 + 异步任务提速
GlobalExecutor.submitServiceUpdateManager(new UpdatedServiceProcessor());
if (emptyServiceAutoClean) {
Loggers.SRV_LOG.info("open empty service auto clean job, initialDelay : {} ms, period : {} ms", cleanEmptyServiceDelay, cleanEmptyServicePeriod);
//delay 60s, period 20s;
//This task is not recommended to be performed frequently in order to avoid
//the possibility that the service cache information may just be deleted
//and then created due to the heartbeat mechanism
GlobalExecutor.scheduleServiceAutoClean(new EmptyServiceAutoClean(), cleanEmptyServiceDelay, cleanEmptyServicePeriod);
}
try {
Loggers.SRV_LOG.info("listen for service meta change");
consistencyService.listen(KeyBuilder.SERVICE_META_KEY_PREFIX, this);
} catch (NacosException e) {
Loggers.SRV_LOG.error("listen for service meta change failed!");
}
}
...
}
public class GlobalExecutor {
private static final ScheduledExecutorService SERVICE_SYNCHRONIZATION_EXECUTOR =
ExecutorFactory.Managed.newSingleScheduledExecutorService(
ClassUtils.getCanonicalName(NamingApp.class),
new NameThreadFactory("com.alibaba.nacos.naming.service.worker")
);
public static final ScheduledExecutorService SERVICE_UPDATE_MANAGER_EXECUTOR =
ExecutorFactory.Managed.newSingleScheduledExecutorService(
ClassUtils.getCanonicalName(NamingApp.class),
new NameThreadFactory("com.alibaba.nacos.naming.service.update.processor")
);
...
public static void scheduleServiceReporter(Runnable command, long delay, TimeUnit unit) {
//在指定的延迟后执行某项任务
SERVICE_SYNCHRONIZATION_EXECUTOR.schedule(command, delay, unit);
}
public static void submitServiceUpdateManager(Runnable runnable) {
//向线程池提交任务，让线程池执行任务
SERVICE_UPDATE_MANAGER_EXECUTOR.submit(runnable);
}
...
}
public final class ExecutorFactory {
...
public static final class Managed {
private static final String DEFAULT_NAMESPACE = "nacos";
private static final ThreadPoolManager THREAD_POOL_MANAGER = ThreadPoolManager.getInstance();
...
//Create a new single scheduled executor service with input thread factory and register to manager.
public static ScheduledExecutorService newSingleScheduledExecutorService(final String group, final ThreadFactory threadFactory) {
ScheduledExecutorService executorService = Executors.newScheduledThreadPool(1, threadFactory);
THREAD_POOL_MANAGER.register(DEFAULT_NAMESPACE, group, executorService);
return executorService;
}
...
}
}
//线程池管理器
public final class ThreadPoolManager {
private Map<String, Map<String, Set<ExecutorService>>> resourcesManager;
private Map<String, Object> lockers = new ConcurrentHashMap<String, Object>(8);
private static final ThreadPoolManager INSTANCE = new ThreadPoolManager();
private static final AtomicBoolean CLOSED = new AtomicBoolean(false);
static {
INSTANCE.init();
//JVM关闭时添加勾子，释放线程资源
ThreadUtils.addShutdownHook(new Thread(new Runnable() {
@Override
public void run() {
LOGGER.warn("[ThreadPoolManager] Start destroying ThreadPool");
//关闭线程池管理器
shutdown();
LOGGER.warn("[ThreadPoolManager] Destruction of the end");
}
}));
}
public static ThreadPoolManager getInstance() {
return INSTANCE;
}
private ThreadPoolManager() {
}
private void init() {
resourcesManager = new ConcurrentHashMap<String, Map<String, Set<ExecutorService>>>(8);
}
//Register the thread pool resources with the resource manager.
public void register(String namespace, String group, ExecutorService executor) {
if (!resourcesManager.containsKey(namespace)) {
synchronized (this) {
lockers.put(namespace, new Object());
}
}
final Object monitor = lockers.get(namespace);
synchronized (monitor) {
Map<String, Set<ExecutorService>> map = resourcesManager.get(namespace);
if (map == null) {
map = new HashMap<String, Set<ExecutorService>>(8);
map.put(group, new HashSet<ExecutorService>());
map.get(group).add(executor);
resourcesManager.put(namespace, map);
return;
}
if (!map.containsKey(group)) {
map.put(group, new HashSet<ExecutorService>());
}
map.get(group).add(executor);
}
}
//Shutdown thread pool manager. 关闭线程池管理器
public static void shutdown() {
if (!CLOSED.compareAndSet(false, true)) {
return;
}
Set<String> namespaces = INSTANCE.resourcesManager.keySet();
for (String namespace : namespaces) {
//销毁所有线程池资源
INSTANCE.destroy(namespace);
}
}
//Destroys all thread pool resources under this namespace.
public void destroy(final String namespace) {
final Object monitor = lockers.get(namespace);
if (monitor == null) {
return;
}
synchronized (monitor) {
Map<String, Set<ExecutorService>> subResource = resourcesManager.get(namespace);
if (subResource == null) {
return;
}
for (Map.Entry<String, Set<ExecutorService>> entry : subResource.entrySet()) {
for (ExecutorService executor : entry.getValue()) {
//关闭线程池
ThreadUtils.shutdownThreadPool(executor);
}
}
resourcesManager.get(namespace).clear();
resourcesManager.remove(namespace);
}
}
...
}
public final class ThreadUtils {
...
public static void addShutdownHook(Runnable runnable) {
Runtime.getRuntime().addShutdownHook(new Thread(runnable));
}
public static void shutdownThreadPool(ExecutorService executor) {
shutdownThreadPool(executor, null);
}
//Shutdown thread pool.
public static void shutdownThreadPool(ExecutorService executor, Logger logger) {
executor.shutdown();
int retry = 3;
while (retry > 0) {
retry--;
try {
if (executor.awaitTermination(1, TimeUnit.SECONDS)) {
return;
}
} catch (InterruptedException e) {
executor.shutdownNow();
Thread.interrupted();
} catch (Throwable ex) {
if (logger != null) {
logger.error("ThreadPoolManager shutdown executor has error : {}", ex);
}
}
}
executor.shutdownNow();
}
...
}

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(3)集群节点收到健康检查请求后的数据同步源码
集群节点收到某集群节点发来的"/v1/core/cluster/report"请求后，会调用NacosClusterController的report()方法来处理请求。在report()方法中，会把发起请求的来源节点状态直接设置成UP状态，然后调用ServerMemberManager的update()方法来更新来源节点属性。在update()方法中，会把存放在serverList中对应的节点Member进行更新，也就是通过MemberUtil的copy()方法覆盖老对象的属性来实现更新。

注意：因为serverList属性在集群中的每个节点都存在一份，所以节点收到健康检查请求后，要对其serverList属性中的节点进行更新。

//Core manager storing all services in Nacos.
@Component
public class ServiceManager implements RecordListener<Service> {
//Map(namespace, Map(group::serviceName, Service)).
private final Map<String, Map<String, Service>> serviceMap = new ConcurrentHashMap<>();
private final DistroMapper distroMapper;
private final Synchronizer synchronizer = new ServiceStatusSynchronizer();
...
public Map<String, Set<String>> getAllServiceNames() {
Map<String, Set<String>> namesMap = new HashMap<>(16);
for (String namespaceId : serviceMap.keySet()) {
namesMap.put(namespaceId, serviceMap.get(namespaceId).keySet());
}
return namesMap;
}
private class ServiceReporter implements Runnable {
@Override
public void run() {
try {
//获取内存注册表下的所有服务名称，按命名空间分类
Map<String, Set<String>> allServiceNames = getAllServiceNames();
if (allServiceNames.size() <= 0) {
//ignore
return;
}
//遍历allServiceNames中的内容
//也就是遍历每一个命名空间，然后封装请求参数，接着发送请求来同步心跳健康检查结果
for (String namespaceId : allServiceNames.keySet()) {
ServiceChecksum checksum = new ServiceChecksum(namespaceId);
//第一个循环：封装请求参数
for (String serviceName : allServiceNames.get(namespaceId)) {
//采用同样的算法，确保当前的集群节点，只对自己负责的那些Service，同步心跳健康检查结果
if (!distroMapper.responsible(serviceName)) {
continue;
}
Service service = getService(namespaceId, serviceName);
if (service == null || service.isEmpty()) {
continue;
}
service.recalculateChecksum();
//添加请求参数
checksum.addItem(serviceName, service.getChecksum());
}
//创建请求参数对象Message，准备进行同步
Message msg = new Message();
//对请求对象进行JSON序列化
msg.setData(JacksonUtils.toJson(checksum));
Collection<Member> sameSiteServers = memberManager.allMembers();
if (sameSiteServers == null || sameSiteServers.size() <= 0) {
return;
}
//第二个循环：遍历所有集群节点，发送请求给其他节点进行数据同步
for (Member server : sameSiteServers) {
//判断地址是否是本节点，如果是则直接跳过
if (server.getAddress().equals(NetUtils.localServer())) {
continue;
}
//同步其他集群节点
synchronizer.send(server.getAddress(), msg);
}
}
} catch (Exception e) {
Loggers.SRV_LOG.error("[DOMAIN-STATUS] Exception while sending service status", e);
} finally {
//继续提交一个延时执行的任务
GlobalExecutor.scheduleServiceReporter(this, switchDomain.getServiceStatusSynchronizationPeriodMillis(), TimeUnit.MILLISECONDS);
}
}
}
...
}
public class ServiceStatusSynchronizer implements Synchronizer {
@Override
public void send(final String serverIP, Message msg) {
if (serverIP == null) {
return;
}
//构建请求参数
Map<String, String> params = new HashMap<String, String>(10);
params.put("statuses", msg.getData());
params.put("clientIP", NetUtils.localServer());
//拼接url地址
String url = "http://" + serverIP + ":" + EnvUtil.getPort() + EnvUtil.getContextPath() + UtilsAndCommons.NACOS_NAMING_CONTEXT + "/service/status";
if (IPUtil.containsPort(serverIP)) {
url = "http://" + serverIP + EnvUtil.getContextPath() + UtilsAndCommons.NACOS_NAMING_CONTEXT + "/service/status";
}
try {
//异步发送HTTP请求，url地址就是：http://ip/v1/ns/service/status, 用来同步心跳健康检查结果
HttpClient.asyncHttpPostLarge(url, null, JacksonUtils.toJson(params), new Callback<String>() {
@Override
public void onReceive(RestResult<String> result) {
if (!result.ok()) {
Loggers.SRV_LOG.warn("[STATUS-SYNCHRONIZE] failed to request serviceStatus, remote server: {}", serverIP);
}
}
@Override
public void onError(Throwable throwable) {
Loggers.SRV_LOG.warn("[STATUS-SYNCHRONIZE] failed to request serviceStatus, remote server: " + serverIP, throwable);
}
@Override
public void onCancel() {
}
});
} catch (Exception e) {
Loggers.SRV_LOG.warn("[STATUS-SYNCHRONIZE] failed to request serviceStatus, remote server: " + serverIP, e);
}
}
...
}
//Service operation controller.
@RestController
@RequestMapping(UtilsAndCommons.NACOS_NAMING_CONTEXT + "/service")
public class ServiceController {
@Autowired
protected ServiceManager serviceManager;
...
//Check service status whether latest.
@PostMapping("/status")
public String serviceStatus(HttpServletRequest request) throws Exception {
String entity = IoUtils.toString(request.getInputStream(), "UTF-8");
String value = URLDecoder.decode(entity, "UTF-8");
JsonNode json = JacksonUtils.toObj(value);
String statuses = json.get("statuses").asText();
String serverIp = json.get("clientIP").asText();
if (!memberManager.hasMember(serverIp)) {
throw new NacosException(NacosException.INVALID_PARAM, "ip: " + serverIp + " is not in serverlist");
}
try {
ServiceManager.ServiceChecksum checksums = JacksonUtils.toObj(statuses, ServiceManager.ServiceChecksum.class);
if (checksums == null) {
Loggers.SRV_LOG.warn("[DOMAIN-STATUS] receive malformed data: null");
return "fail";
}
for (Map.Entry<String, String> entry : checksums.serviceName2Checksum.entrySet()) {
if (entry == null || StringUtils.isEmpty(entry.getKey()) || StringUtils.isEmpty(entry.getValue())) {
continue;
}
String serviceName = entry.getKey();
String checksum = entry.getValue();
Service service = serviceManager.getService(checksums.namespaceId, serviceName);
if (service == null) {
continue;
}
service.recalculateChecksum();
//通过对比入参和注册表的checksum，如果发现服务状态有变动
if (!checksum.equals(service.getChecksum())) {
if (Loggers.SRV_LOG.isDebugEnabled()) {
Loggers.SRV_LOG.debug("checksum of {} is not consistent, remote: {}, checksum: {}, local: {}", serviceName, serverIp, checksum, service.getChecksum());
}
//添加到阻塞队列
serviceManager.addUpdatedServiceToQueue(checksums.namespaceId, serviceName, serverIp, checksum);
}
}
} catch (Exception e) {
Loggers.SRV_LOG.warn("[DOMAIN-STATUS] receive malformed data: " + statuses, e);
}
return "ok";
}
...
}
//Core manager storing all services in Nacos.
@Component
public class ServiceManager implements RecordListener<Service> {
private final Lock lock = new ReentrantLock();
//阻塞队列
private final LinkedBlockingDeque<ServiceKey> toBeUpdatedServicesQueue = new LinkedBlockingDeque<>(1024 * 1024);
...
//Add a service into queue to update.
public void addUpdatedServiceToQueue(String namespaceId, String serviceName, String serverIP, String checksum) {
lock.lock();
try {
//包装成ServiceKey对象，放入到toBeUpdatedServicesQueue阻塞队列中
toBeUpdatedServicesQueue.offer(new ServiceKey(namespaceId, serviceName, serverIP, checksum), 5, TimeUnit.MILLISECONDS);
} catch (Exception e) {
toBeUpdatedServicesQueue.poll();
toBeUpdatedServicesQueue.add(new ServiceKey(namespaceId, serviceName, serverIP, checksum));
Loggers.SRV_LOG.error("[DOMAIN-STATUS] Failed to add service to be updated to queue.", e);
} finally {
lock.unlock();
}
}
...
}

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(4)总结
在Nacos集群架构下，集群节点间的健康状态如何进行同步。简单来说，集群节点间是会相互进行通信的。如果通信失败，那么就会把通信节点的状态属性修改为DOWN。

5.集群新增节点时如何同步已有服务实例数据
(1)节点启动时加载全部服务实例数据的异步任务
(2)节点处理获取全部服务实例数据请求的源码
(3)总结

(1)节点启动时加载服务实例数据的异步任务
Nacos服务端会有一个DistroProtocol类，它是一个Bean对象，在Spring项目启动时会创建这个DistroProtocol类型的Bean。

创建DistroProtocol类型的Bean时，会执行DistroProtocol的构造方法，从而调用DistroProtocol的startLoadTask()方法开启一个加载数据的异步任务。

在DistroProtocol的startLoadTask()方法中，会提交一个异步任务，并且会通过传入一个回调方法来标志是否已初始化成功。其中提交的任务类型是DistroLoadDataTask，所以会执行DistroLoadDataTask的run()方法，接着会执行DistroLoadDataTask的load()方法，然后执行该任务类的loadAllDataSnapshotFromRemote()方法，从而获取其他集群节点上的全部服务实例数据并更新本地注册表。

在loadAllDataSnapshotFromRemote()方法中，首先会遍历除自身节点外的其他集群节点。然后调用DistroHttpAgent的getDatumSnapshot()方法，通过HTTP请求"/v1/ns/distro/datums"获取目标节点的全部服务实例数据。接着再调用DistroConsistencyServiceImpl的processSnapshot()方法，将获取到的全部服务实例数据写入到本地注册表中。其中只要有一个集群节点数据同步成功，那么这个方法就结束。否则就继续遍历下一个集群节点，获取全部服务实例数据然后同步本地。

Nacos服务端在处理服务实例注册时，采用的是内存队列 + 异步任务。异步任务会调用listener的onChange()方法利用写时复制来更新本地注册表。而processSnapshot()方法也会调用listener的onChange()方法来更新注册表，其中listener的onChange()方法对应的实现其实就是Service的onChange()方法。

//Core manager storing all services in Nacos.
@Component
public class ServiceManager implements RecordListener<Service> {
//阻塞队列
private final LinkedBlockingDeque<ServiceKey> toBeUpdatedServicesQueue = new LinkedBlockingDeque<>(1024 * 1024);
...
private class UpdatedServiceProcessor implements Runnable {
//get changed service from other server asynchronously
@Override
public void run() {
ServiceKey serviceKey = null;
try {
//无限循环
while (true) {
try {
//从阻塞队列中获取任务
serviceKey = toBeUpdatedServicesQueue.take();
} catch (Exception e) {
Loggers.EVT_LOG.error("[UPDATE-DOMAIN] Exception while taking item from LinkedBlockingDeque.");
}
if (serviceKey == null) {
continue;
}
GlobalExecutor.submitServiceUpdate(new ServiceUpdater(serviceKey));
}
} catch (Exception e) {
Loggers.EVT_LOG.error("[UPDATE-DOMAIN] Exception while update service: {}", serviceKey, e);
}
}
}
private class ServiceUpdater implements Runnable {
String namespaceId;
String serviceName;
String serverIP;
public ServiceUpdater(ServiceKey serviceKey) {
this.namespaceId = serviceKey.getNamespaceId();
this.serviceName = serviceKey.getServiceName();
this.serverIP = serviceKey.getServerIP();
}
@Override
public void run() {
try {
//修改服务实例的健康状态
updatedHealthStatus(namespaceId, serviceName, serverIP);
} catch (Exception e) {
Loggers.SRV_LOG.warn("[DOMAIN-UPDATER] Exception while update service: {} from {}, error: {}", serviceName, serverIP, e);
}
}
}
//Update health status of instance in service. 修改服务实例的健康状态
public void updatedHealthStatus(String namespaceId, String serviceName, String serverIP) {
Message msg = synchronizer.get(serverIP, UtilsAndCommons.assembleFullServiceName(namespaceId, serviceName));
//解析参数
JsonNode serviceJson = JacksonUtils.toObj(msg.getData());
ArrayNode ipList = (ArrayNode) serviceJson.get("ips");
Map<String, String> ipsMap = new HashMap<>(ipList.size());
for (int i = 0; i < ipList.size(); i++) {
String ip = ipList.get(i).asText();
String[] strings = ip.split("_");
ipsMap.put(strings[0], strings[1]);
}
Service service = getService(namespaceId, serviceName);
if (service == null) {
return;
}
//是否改变标识
boolean changed = false;
//获取全部的实例数据，进行遍历
List<Instance> instances = service.allIPs();
for (Instance instance : instances) {
//同步健康状态结果
boolean valid = Boolean.parseBoolean(ipsMap.get(instance.toIpAddr()));
if (valid != instance.isHealthy()) {
changed = true;
//更新服务实例的健康状态
instance.setHealthy(valid);
Loggers.EVT_LOG.info("{} {SYNC} IP-{} : {}:{}@{}", serviceName, (instance.isHealthy() ? "ENABLED" : "DISABLED"), instance.getIp(), instance.getPort(), instance.getClusterName());
}
}
//如果服务实例健康状态改变了，那么就发布"服务改变事件"，使用UDP方式通知客户端
if (changed) {
pushService.serviceChanged(service);
if (Loggers.EVT_LOG.isDebugEnabled()) {
StringBuilder stringBuilder = new StringBuilder();
List<Instance> allIps = service.allIPs();
for (Instance instance : allIps) {
stringBuilder.append(instance.toIpAddr()).append("_").append(instance.isHealthy()).append(",");
}
Loggers.EVT_LOG.debug("[HEALTH-STATUS-UPDATED] namespace: {}, service: {}, ips: {}", service.getNamespaceId(), service.getName(), stringBuilder.toString());
}
}
}
...
}

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总结：Nacos服务端集群节点启动时，会创建一个DistroProtocol类型的Bean对象，在这个DistroProtocol类型的Bean对象的构造方法会开启一个异步任务。该异步任务的主要逻辑是通过HTTP方式从其他集群节点获取服务数据，然后把获取到的服务实例数据更新到本地的内存注册表，完成数据同步。而且只要成功从某一个集群节点完成数据同步，那整个任务逻辑就结束。

此外，向某个集群节点获取全部服务实例数据时，是向"/v1/ns/distro/datums"接口发起HTTP请求来进行获取的。

(2)节点处理获取全部服务实例数据请求的源码
Nacos集群节点收到"/v1/ns/distro/datums"的HTTP请求后，便会执行DistroController的getAllDatums()方法。也就是调用DistroProtocol的onSnapshot()方法获取数据，然后直接返回。接着会调用DistroDataStorageImpl的getDatumSnapshot()方法。

getDatumSnapshot()方法会从DataStore的getDataMap()方法获取结果。进行服务实例注册时，会把服务实例信息存一份放在DataStore的Map中。进行服务实例同步时，也会把服务实例信息存放到DataStore的Map中。所以在DataStore里，会包含整个服务实例信息的数据。这里获取全部服务实例数据的接口，也是利用DataStore来实现的，而不是从内存注册表中获取。

@DependsOn("ProtocolManager")
@org.springframework.stereotype.Service("distroConsistencyService")
public class DistroConsistencyServiceImpl implements EphemeralConsistencyService, DistroDataProcessor {
private final DistroProtocol distroProtocol;
...
@Override
public void put(String key, Record value) throws NacosException {
//把包含了当前注册的服务实例的、最新的服务实例列表，存储到DataStore对象中，
//并添加异步任务来实现将最新的服务实例列表更新到内存注册表
onPut(key, value);
//在集群架构下，DistroProtocol.sync()方法会进行集群节点的服务实例数据同步
distroProtocol.sync(new DistroKey(key, KeyBuilder.INSTANCE_LIST_KEY_PREFIX), DataOperation.CHANGE, globalConfig.getTaskDispatchPeriod() / 2);
}
...
}
@Component
public class DistroProtocol {
private final ServerMemberManager memberManager;
private final DistroTaskEngineHolder distroTaskEngineHolder;
...
//Start to sync data to all remote server.
public void sync(DistroKey distroKey, DataOperation action, long delay) {
//遍历除自身以外的其他集群节点
for (Member each : memberManager.allMembersWithoutSelf()) {
//包装第一层
DistroKey distroKeyWithTarget = new DistroKey(distroKey.getResourceKey(), distroKey.getResourceType(), each.getAddress());
//包装第二层
DistroDelayTask distroDelayTask = new DistroDelayTask(distroKeyWithTarget, action, delay);
//实际调用的是NacosDelayTaskExecuteEngine.addTask()方法添加任务
distroTaskEngineHolder.getDelayTaskExecuteEngine().addTask(distroKeyWithTarget, distroDelayTask);
if (Loggers.DISTRO.isDebugEnabled()) {
Loggers.DISTRO.debug("[DISTRO-SCHEDULE] {} to {}", distroKey, each.getAddress());
}
}
}
...
}
public class DistroKey {
private String resourceKey;
private String resourceType;
private String targetServer;
public DistroKey() {
}
public DistroKey(String resourceKey, String resourceType, String targetServer) {
this.resourceKey = resourceKey;
this.resourceType = resourceType;
this.targetServer = targetServer;
}
...
}
//Distro delay task.
public class DistroDelayTask extends AbstractDelayTask {
private final DistroKey distroKey;
private DataOperation action;
private long createTime;
public DistroDelayTask(DistroKey distroKey, DataOperation action, long delayTime) {
this.distroKey = distroKey;
this.action = action;
this.createTime = System.currentTimeMillis();
setLastProcessTime(createTime);
setTaskInterval(delayTime);
}
...
}
//Abstract task which can delay and merge.
public abstract class AbstractDelayTask implements NacosTask {
//Task time interval between twice processing, unit is millisecond.
private long taskInterval;
//The time which was processed at last time, unit is millisecond.
private long lastProcessTime;
public void setTaskInterval(long interval) {
this.taskInterval = interval;
}
public void setLastProcessTime(long lastProcessTime) {
this.lastProcessTime = lastProcessTime;
}
...
}
//Distro task engine holder.
@Component
public class DistroTaskEngineHolder {
private final DistroDelayTaskExecuteEngine delayTaskExecuteEngine = new DistroDelayTaskExecuteEngine();
public DistroDelayTaskExecuteEngine getDelayTaskExecuteEngine() {
return delayTaskExecuteEngine;
}
...
}
public class DistroDelayTaskExecuteEngine extends NacosDelayTaskExecuteEngine {
public DistroDelayTaskExecuteEngine() {
super(DistroDelayTaskExecuteEngine.class.getName(), Loggers.DISTRO);
}
...
}
//Nacos delay task execute engine.
public class NacosDelayTaskExecuteEngine extends AbstractNacosTaskExecuteEngine {
private final ScheduledExecutorService processingExecutor;
protected final ConcurrentHashMap<Object, AbstractDelayTask> tasks;//任务池
protected final ReentrantLock lock = new ReentrantLock();
...
public NacosDelayTaskExecuteEngine(String name, int initCapacity, Logger logger, long processInterval) {
super(logger);
tasks = new ConcurrentHashMap<Object, AbstractDelayTask>(initCapacity);
processingExecutor = ExecutorFactory.newSingleScheduledExecutorService(new NameThreadFactory(name));
//开启延时任务
processingExecutor.scheduleWithFixedDelay(new ProcessRunnable(), processInterval, processInterval, TimeUnit.MILLISECONDS);
}
@Override
public void addTask(Object key, AbstractDelayTask newTask) {
lock.lock();
try {
AbstractDelayTask existTask = tasks.get(key);
if (null != existTask) {
newTask.merge(existTask);
}
//最后放入到ConcurrentHashMap中
tasks.put(key, newTask);
} finally {
lock.unlock();
}
}
...
private class ProcessRunnable implements Runnable {
@Override
public void run() {
try {
processTasks();
} catch (Throwable e) {
getEngineLog().error(e.toString(), e);
}
}
}
...
//process tasks in execute engine.
protected void processTasks() {
//获取tasks中所有的任务，然后进行遍历
Collection<Object> keys = getAllTaskKeys();
for (Object taskKey : keys) {
//通过任务key，获取具体的任务，并且从任务池中移除掉
AbstractDelayTask task = removeTask(taskKey);
if (null == task) {
continue;
}
//根据taskKey获取NacosTaskProcessor延迟任务处理器：DistroDelayTaskProcessor
NacosTaskProcessor processor = getProcessor(taskKey);
if (null == processor) {
getEngineLog().error("processor not found for task, so discarded. " + task);
continue;
}
try {
//ReAdd task if process failed
//调用DistroDelayTaskProcessor.process()方法，把task同步任务放入到第二层内存队列中
if (!processor.process(task)) {
//如果失败了，会重试添加task回tasks这个map中
retryFailedTask(taskKey, task);
}
} catch (Throwable e) {
getEngineLog().error("Nacos task execute error : " + e.toString(), e);
retryFailedTask(taskKey, task);
}
}
}
@Override
public AbstractDelayTask removeTask(Object key) {
lock.lock();
try {
AbstractDelayTask task = tasks.get(key);
if (null != task && task.shouldProcess()) {
return tasks.remove(key);
} else {
return null;
}
} finally {
lock.unlock();
}
}
}

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注意：DataStore数据最后还是存到内存的。通过使用DataStore，可以实现以下功能和好处：

一.数据持久化
DataStore可将节点数据持久化到磁盘或其他介质，以确保数据的持久性。这样即使系统重启或发生故障，节点数据也能够得到恢复和保留。毕竟Datum的key是ServiceName、value是Instance实例列表，而Instance实例中又会包含所属的ClusterName、IP和Port，所以根据DataStore可以恢复完整的内存注册表。

//Distro delay task processor.
public class DistroDelayTaskProcessor implements NacosTaskProcessor {
private final DistroTaskEngineHolder distroTaskEngineHolder;
private final DistroComponentHolder distroComponentHolder;
public DistroDelayTaskProcessor(DistroTaskEngineHolder distroTaskEngineHolder, DistroComponentHolder distroComponentHolder) {
this.distroTaskEngineHolder = distroTaskEngineHolder;
this.distroComponentHolder = distroComponentHolder;
}
@Override
public boolean process(NacosTask task) {
if (!(task instanceof DistroDelayTask)) {
return true;
}
//将NacosTask任务对象转换为DistroDelayTask任务对象
DistroDelayTask distroDelayTask = (DistroDelayTask) task;
DistroKey distroKey = distroDelayTask.getDistroKey();
if (DataOperation.CHANGE.equals(distroDelayTask.getAction())) {
//包装成一个DistroSyncChangeTask对象
DistroSyncChangeTask syncChangeTask = new DistroSyncChangeTask(distroKey, distroComponentHolder);
//调用NacosExecuteTaskExecuteEngine.addTask()方法添加到队列中去
distroTaskEngineHolder.getExecuteWorkersManager().addTask(distroKey, syncChangeTask);
return true;
}
return false;
}
}
//Nacos execute task execute engine.
public class NacosExecuteTaskExecuteEngine extends AbstractNacosTaskExecuteEngine {
private final TaskExecuteWorker[] executeWorkers;
public NacosExecuteTaskExecuteEngine(String name, Logger logger, int dispatchWorkerCount) {
super(logger);
//TaskExecuteWorker在初始化时会启动一个线程处理其队列中的任务
executeWorkers = new TaskExecuteWorker[dispatchWorkerCount];
for (int mod = 0; mod < dispatchWorkerCount; ++mod) {
executeWorkers[mod] = new TaskExecuteWorker(name, mod, dispatchWorkerCount, getEngineLog());
}
}
...
@Override
public void addTask(Object tag, AbstractExecuteTask task) {
//根据tag获取到TaskExecuteWorker
NacosTaskProcessor processor = getProcessor(tag);
if (null != processor) {
processor.process(task);
return;
}
TaskExecuteWorker worker = getWorker(tag);
//调用TaskExecuteWorker.process()方法把DistroSyncChangeTask任务放入到队列当中去
worker.process(task);
}
private TaskExecuteWorker getWorker(Object tag) {
int idx = (tag.hashCode() & Integer.MAX_VALUE) % workersCount();
return executeWorkers[idx];
}
...
}
//Nacos execute task execute worker.
public final class TaskExecuteWorker implements NacosTaskProcessor, Closeable {
//任务存储容器
private final BlockingQueue<Runnable> queue;
public TaskExecuteWorker(final String name, final int mod, final int total, final Logger logger) {
this.name = name + "_" + mod + "%" + total;
this.queue = new ArrayBlockingQueue<Runnable>(QUEUE_CAPACITY);
this.closed = new AtomicBoolean(false);
this.log = null == logger ? LoggerFactory.getLogger(TaskExecuteWorker.class) : logger;
new InnerWorker(name).start();
}
...
@Override
public boolean process(NacosTask task) {
if (task instanceof AbstractExecuteTask) {
//把DistroSyncChangeTask任务放入到队列中
putTask((Runnable) task);
}
return true;
}
private void putTask(Runnable task) {
try {
//把DistroSyncChangeTask任务放入到队列中
queue.put(task);
} catch (InterruptedException ire) {
log.error(ire.toString(), ire);
}
}
...
//Inner execute worker.
private class InnerWorker extends Thread {
InnerWorker(String name) {
setDaemon(false);
setName(name);
}
@Override
public void run() {
while (!closed.get()) {
try {
//一直取队列中的任务，这里的task任务类型是：DistroSyncChangeTask
Runnable task = queue.take();
long begin = System.currentTimeMillis();
//调用DistroSyncChangeTask中的run方法
task.run();
long duration = System.currentTimeMillis() - begin;
if (duration > 1000L) {
log.warn("distro task {} takes {}ms", task, duration);
}
} catch (Throwable e) {
log.error("[DISTRO-FAILED] " + e.toString(), e);
}
}
}
}
}

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二.数据同步
DataStore可以协调和同步节点数据的访问和更新。当多个节点同时注册或更新数据时，DataStore可确保数据的一致性和正确性，避免数据冲突和不一致的情况。

三.数据管理
DataStore提供了对节点数据的管理功能，包括增加、更新、删除等操作。通过使用适当的数据结构和算法，可以高效地管理大量的节点数据，并支持快速的数据访问和查询。

四.数据访问控制
DataStore可以实现对节点数据的访问控制和权限管理，只有具有相应权限的节点或用户才能访问和修改特定的节点数据，提高数据的安全性和保密性。

DataStore在Nacos中充当了节点数据的中央存储和管理器。通过提供持久化 + 同步 + 管理 + 访问控制等功能，确保节点数据的可靠性 + 一致性 + 安全性，是实现节点数据存储和操作的核心组件之一。

(3)总结
Nacos集群架构下新增一个集群节点时，新节点会如何进行服务数据同步：

首先利用了DistroProtocol类的Bean对象的构造方法开启异步任务，通过HTTP方式去请求其他集群节点的全部数据。

当新节点获取全部数据后，会调用Service的onChange()方法，然后利用写时复制机制更新本地内存注册表。

Nacos集群节点在处理获取全部服务实例数据的请求时，并不是从内存注册表中获取的，而是通过DataStore来获取。

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