类图

Eureka Client类图

初始化

初始化 DiscoveryClient

@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
                Provider<BackupRegistry> backupRegistryProvider) {
   // ... 省略细致末节
   // 是否需要获取注册表信息
    if (config.shouldFetchRegistry()) {
        this.registryStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRY_PREFIX + "lastUpdateSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
    } else {
        this.registryStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;
    }
        // 是否需要注册到Eureka
    if (config.shouldRegisterWithEureka()) {
        this.heartbeatStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRATION_PREFIX + "lastHeartbeatSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
    } else {
        this.heartbeatStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;
    }

    logger.info("Initializing Eureka in region {}", clientConfig.getRegion());
        
    // 既不需要注册到Eureka 也不需要获取注册表 记录日志并return结束初始化
    if (!config.shouldRegisterWithEureka() && !config.shouldFetchRegistry()) {
        logger.info("Client configured to neither register nor query for data.");
        scheduler = null;
        heartbeatExecutor = null;
        cacheRefreshExecutor = null;
        eurekaTransport = null;
        instanceRegionChecker = new InstanceRegionChecker(new PropertyBasedAzToRegionMapper(config), clientConfig.getRegion());

        // This is a bit of hack to allow for existing code using DiscoveryManager.getInstance()
        // to work with DI'd DiscoveryClient
        DiscoveryManager.getInstance().setDiscoveryClient(this);
        DiscoveryManager.getInstance().setEurekaClientConfig(config);

        initTimestampMs = System.currentTimeMillis();
        logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}",
                initTimestampMs, this.getApplications().size());

        return;  // no need to setup up an network tasks and we are done
    }

    try {
        // 初始化定时线程池，默认大小为2， 心跳和缓存刷新各1个
        // default size of 2 - 1 each for heartbeat and cacheRefresh
        scheduler = Executors.newScheduledThreadPool(2,
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-%d")
                        .setDaemon(true)
                        .build());

        heartbeatExecutor = new ThreadPoolExecutor(
                1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
                new SynchronousQueue<Runnable>(),
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
                        .setDaemon(true)
                        .build()
        );  // use direct handoff

        cacheRefreshExecutor = new ThreadPoolExecutor(
                1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
                new SynchronousQueue<Runnable>(),
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
                        .setDaemon(true)
                        .build()
        );  // use direct handoff

        eurekaTransport = new EurekaTransport();
        scheduleServerEndpointTask(eurekaTransport, args);

        AzToRegionMapper azToRegionMapper;
        if (clientConfig.shouldUseDnsForFetchingServiceUrls()) {
            azToRegionMapper = new DNSBasedAzToRegionMapper(clientConfig);
        } else {
            azToRegionMapper = new PropertyBasedAzToRegionMapper(clientConfig);
        }
        if (null != remoteRegionsToFetch.get()) {
            azToRegionMapper.setRegionsToFetch(remoteRegionsToFetch.get().split(","));
        }
        instanceRegionChecker = new InstanceRegionChecker(azToRegionMapper, clientConfig.getRegion());
    } catch (Throwable e) {
        throw new RuntimeException("Failed to initialize DiscoveryClient!", e);
    }

    // 需要获取注册表信息 && 获取增量注册信息
    // 如果fetchRegistry获取注册信息失败，认为所有的Eureka Server无法成功通信
    // 那么会从备份注册信息处获取注册信息
    if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
        fetchRegistryFromBackup();
    }

    // call and execute the pre registration handler before all background tasks (inc registration) is started
    if (this.preRegistrationHandler != null) {
        this.preRegistrationHandler.beforeRegistration();
    }

    // 需要注册到Eureka && 需要在初始化时强制注册
    if (clientConfig.shouldRegisterWithEureka() && clientConfig.shouldEnforceRegistrationAtInit()) {
        try {
            // 因为是强制注册，如果注册失败，应该抛出异常
            if (!register() ) {
                throw new IllegalStateException("Registration error at startup. Invalid server response.");
            }
        } catch (Throwable th) {
            logger.error("Registration error at startup: {}", th.getMessage());
            throw new IllegalStateException(th);
        }
    }

    // finally, init the schedule tasks (e.g. cluster resolvers, heartbeat, instanceInfo replicator, fetch
    // 初始化定时线程池中的任务，心跳、实例信息同步和获取注册信息
    // 创建实例状态变更监听事件 
    initScheduledTasks();

    try {
        Monitors.registerObject(this);
    } catch (Throwable e) {
        logger.warn("Cannot register timers", e);
    }

    // This is a bit of hack to allow for existing code using DiscoveryManager.getInstance()
    // to work with DI'd DiscoveryClient
    DiscoveryManager.getInstance().setDiscoveryClient(this);
    DiscoveryManager.getInstance().setEurekaClientConfig(config);

    // ...
}

开启定时线程任务 void initScheduledTasks()

private void initScheduledTasks() {
    // 需要获取注册表信息 开启定时缓存刷新线程CacheRefreshThread
    if (clientConfig.shouldFetchRegistry()) {
        // registry cache refresh timer
        int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
        int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
        scheduler.schedule(
                new TimedSupervisorTask(
                        "cacheRefresh",
                        scheduler,
                        cacheRefreshExecutor,
                        registryFetchIntervalSeconds,
                        TimeUnit.SECONDS,
                        expBackOffBound,
                        new CacheRefreshThread()
                ),
                registryFetchIntervalSeconds, TimeUnit.SECONDS);
    }

    // 需要注册到Eureka 开启定时心跳线程HeartbeatThread
    if (clientConfig.shouldRegisterWithEureka()) {
        int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
        int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
        logger.info("Starting heartbeat executor: " + "renew interval is: {}", renewalIntervalInSecs);

        // 开启定时心跳线程HeartbeatThread
        scheduler.schedule(
                new TimedSupervisorTask(
                        "heartbeat",
                        scheduler,
                        heartbeatExecutor,
                        renewalIntervalInSecs,
                        TimeUnit.SECONDS,
                        expBackOffBound,
                        new HeartbeatThread()
                ),
                renewalIntervalInSecs, TimeUnit.SECONDS);

        // InstanceInfo replicator
        instanceInfoReplicator = new InstanceInfoReplicator(
                this,
                instanceInfo,
                clientConfig.getInstanceInfoReplicationIntervalSeconds(),
                2); // burstSize

        // 监听实例的状态变更
        statusChangeListener = new ApplicationInfoManager.StatusChangeListener() {
            @Override
            public String getId() {
                return "statusChangeListener";
            }

            @Override
            public void notify(StatusChangeEvent statusChangeEvent) {
                // 监听状态变更
                if (InstanceStatus.DOWN == statusChangeEvent.getStatus() ||
                        InstanceStatus.DOWN == statusChangeEvent.getPreviousStatus()) {
                    // log at warn level if DOWN was involved
                    logger.warn("Saw local status change event {}", statusChangeEvent);
                } else {
                    logger.info("Saw local status change event {}", statusChangeEvent);
                }
                instanceInfoReplicator.onDemandUpdate();
            }
        };

        if (clientConfig.shouldOnDemandUpdateStatusChange()) {
            applicationInfoManager.registerStatusChangeListener(statusChangeListener);
        }

        instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
    } else {
        logger.info("Not registering with Eureka server per configuration");
    }
}

续租renew()

在初始化时，如果Eureka需要注册到Eureka Server上，会开启定时HeartbeatThread。HeartbeatThread中核心的方法为renew()方法。第一次renew时，服务端返回404，会触发当前实例的注册操作，并且设置实例的dirty flag为false。

private class HeartbeatThread implements Runnable {

    public void run() {
        if (renew()) {
            lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis();
        }
    }
}

boolean renew() {
        EurekaHttpResponse<InstanceInfo> httpResponse;
        try {
            // 向Eureka Server发送基于REST的请求
            httpResponse = eurekaTransport.registrationClient.sendHeartBeat(instanceInfo.getAppName(), instanceInfo.getId(), instanceInfo, null);
            logger.debug(PREFIX + "{} - Heartbeat status: {}", appPathIdentifier, httpResponse.getStatusCode());
            // 如果返回状态值为404，代表当前实例尚未注册到Eureka上，会进行注册
            if (httpResponse.getStatusCode() == Status.NOT_FOUND.getStatusCode()) {
                REREGISTER_COUNTER.increment();
                logger.info(PREFIX + "{} - Re-registering apps/{}", appPathIdentifier, instanceInfo.getAppName());
                long timestamp = instanceInfo.setIsDirtyWithTime();
                // 注册
                boolean success = register();
                if (success) {
                    // 设置实例的dirty flag为false
                    instanceInfo.unsetIsDirty(timestamp);
                }
                return success;
            }
            // 如果返回状态值不为404，判断是否是200，代表成功renew
            return httpResponse.getStatusCode() == Status.OK.getStatusCode();
        } catch (Throwable e) {
            logger.error(PREFIX + "{} - was unable to send heartbeat!", appPathIdentifier, e);
            return false;
        }
    }

注册register()

boolean register() throws Throwable {
    logger.info(PREFIX + "{}: registering service...", appPathIdentifier);
    EurekaHttpResponse<Void> httpResponse;
    try {
        // 基于REST发送注册请求
        httpResponse = eurekaTransport.registrationClient.register(instanceInfo);
    } catch (Exception e) {
        logger.warn(PREFIX + "{} - registration failed {}", appPathIdentifier, e.getMessage(), e);
        throw e;
    }
    if (logger.isInfoEnabled()) {
        logger.info(PREFIX + "{} - registration status: {}", appPathIdentifier, httpResponse.getStatusCode());
    }
    // 判断是否注册成功（Status.NO_CONTENT
    return httpResponse.getStatusCode() == Status.NO_CONTENT.getStatusCode();
}

刷新注册信息refreshRegistry()

会首先判断最近的区域节点是否发生变更，如果发生变更会更新这个信息，同时需要全量的同步注册信息，否则只进行增量的注册信息更新。

class CacheRefreshThread implements Runnable {
    public void run() {
        refreshRegistry();
    }
}

 @VisibleForTesting
    void refreshRegistry() {
        try {
            boolean isFetchingRemoteRegionRegistries = isFetchingRemoteRegionRegistries();

            boolean remoteRegionsModified = false;
            // This makes sure that a dynamic change to remote regions to fetch is honored.
            // 确保动态变更最近的远程区域来获取数据
            String latestRemoteRegions = clientConfig.fetchRegistryForRemoteRegions();
            if (null != latestRemoteRegions) {
                String currentRemoteRegions = remoteRegionsToFetch.get();
                if (!latestRemoteRegions.equals(currentRemoteRegions)) {
                    // Both remoteRegionsToFetch and AzToRegionMapper.regionsToFetch need to be in sync
                    synchronized (instanceRegionChecker.getAzToRegionMapper()) {
                        if (remoteRegionsToFetch.compareAndSet(currentRemoteRegions, latestRemoteRegions)) {
                            String[] remoteRegions = latestRemoteRegions.split(",");
                            remoteRegionsRef.set(remoteRegions);
                            instanceRegionChecker.getAzToRegionMapper().setRegionsToFetch(remoteRegions);
                            remoteRegionsModified = true;
                        } else {
                            logger.info("Remote regions to fetch modified concurrently," +
                                    " ignoring change from {} to {}", currentRemoteRegions, latestRemoteRegions);
                        }
                    }
                } else {
                    // Just refresh mapping to reflect any DNS/Property change
                    instanceRegionChecker.getAzToRegionMapper().refreshMapping();
                }
            }
          
            // ！！！获取注册信息，如果远程区域发生变更需要全量更新，或者增量更新
            boolean success = fetchRegistry(remoteRegionsModified);
            if (success) {
                // 更新注册实例列表大小
                registrySize = localRegionApps.get().size();
                // 更新最近一次获取到注册信息的时间戳
                lastSuccessfulRegistryFetchTimestamp = System.currentTimeMillis();
            }
                        
            // ...
        } catch (Throwable e) {
            logger.error("Cannot fetch registry from server", e);
        }
    }

下线shutdown()

@PreDestroy
@Override
public synchronized void shutdown() {
    if (isShutdown.compareAndSet(false, true)) {
        logger.info("Shutting down DiscoveryClient ...");
                // 取消监听器
        if (statusChangeListener != null && applicationInfoManager != null) {
            applicationInfoManager.unregisterStatusChangeListener(statusChangeListener.getId());
        }
                
        // 关闭定时任务
        cancelScheduledTasks();

        // If APPINFO was registered
        if (applicationInfoManager != null
                && clientConfig.shouldRegisterWithEureka()
                && clientConfig.shouldUnregisterOnShutdown()) {
            // 更新应用状态为DOWN下线
            applicationInfoManager.setInstanceStatus(InstanceStatus.DOWN);
            // 注销
            unregister();
        }
                
        // 关闭eurekaTransport
        if (eurekaTransport != null) {
            eurekaTransport.shutdown();
        }
                
        heartbeatStalenessMonitor.shutdown();
        registryStalenessMonitor.shutdown();

        logger.info("Completed shut down of DiscoveryClient");
    }
}

// 注销
void unregister() {
  // It can be null if shouldRegisterWithEureka == false
  if(eurekaTransport != null && eurekaTransport.registrationClient != null) {
    try {
      logger.info("Unregistering ...");
      // 发送基于REST的注销请求
      EurekaHttpResponse<Void> httpResponse = eurekaTransport.registrationClient.cancel(instanceInfo.getAppName(), instanceInfo.getId());
      logger.info(PREFIX + "{} - deregister  status: {}", appPathIdentifier, httpResponse.getStatusCode());
    } catch (Exception e) {
      logger.error(PREFIX + "{} - de-registration failed{}", appPathIdentifier, e.getMessage(), e);
    }
  }
}