一起学源码-微服务Nexflix Eureka 源码三：EurekaServer启动之EurekaServer上下文EurekaClient创建

Posted 2021-03-20 wang-meng

前言

上篇文章已经介绍了 Eureka Server 环境和上下文初始化的一些代码，其中重点讲解了environment初始化使用的单例模式，以及EurekaServerConfigure基于接口对外暴露配置方法的设计方式。这一讲就是讲解Eureka Server上下文初始化剩下的内容：Eureka Client初始化。

如若转载 请标明来源：一枝花算不算浪漫

EurekaServer上下文构建之Client

EurekaClientConfigure创建过程

因为eurekaSever是集群部署的，所以每个eurekaServer都需要注册到其他注册中心节点。这里自己既是一个eurekaServer，也是一个eurekaClient。

截取EurekaServer中初始化上下文代码：

// 3、初始化eureka-server内部的一个eureka-client（用来跟其他的eureka-server节点做注册和通信）
// 类的开头已经说明了：EurekaInstanceConfig其实就是eureka client相关的配置类
if (eurekaClient == null) {
    EurekaInstanceConfig instanceConfig = isCloud(ConfigurationManager.getDeploymentContext())
            ? new CloudInstanceConfig()
            : new MyDataCenterInstanceConfig();
    
    applicationInfoManager = new ApplicationInfoManager(
            instanceConfig, new EurekaConfigBasedInstanceInfoProvider(instanceConfig).get());

    // DefaultEurekaClientConfig类似于上面的DefaultEurekaServerConfig类实现
    EurekaClientConfig eurekaClientConfig = new DefaultEurekaClientConfig();
    eurekaClient = new DiscoveryClient(applicationInfoManager, eurekaClientConfig);
} else {
    applicationInfoManager = eurekaClient.getApplicationInfoManager();
}

再看下eurekaClientConfig创建的代码：

public DefaultEurekaClientConfig(String namespace) {
    this.namespace = namespace.endsWith(".")
            ? namespace
            : namespace + ".";

    this.configInstance = Archaius1Utils.initConfig(CommonConstants.CONFIG_FILE_NAME);
    this.transportConfig = new DefaultEurekaTransportConfig(namespace, configInstance);
}

public static DynamicPropertyFactory initConfig(String configName) {

    DynamicPropertyFactory configInstance = DynamicPropertyFactory.getInstance();
    /**
     * 获取eureka client配置文件，类似于 {@link DefaultEurekaServerConfig}中的：
     * String eurekaPropsFile = EUREKA_PROPS_FILE.get();
     * private static final DynamicStringProperty EUREKA_PROPS_FILE = DynamicPropertyFactory
     *             .getInstance().getStringProperty("eureka.server.props","eureka-server");
     */
    DynamicStringProperty EUREKA_PROPS_FILE = configInstance.getStringProperty("eureka.client.props", configName);

    String env = ConfigurationManager.getConfigInstance().getString(EUREKA_ENVIRONMENT, "test");
    ConfigurationManager.getConfigInstance().setProperty(ARCHAIUS_DEPLOYMENT_ENVIRONMENT, env);

    String eurekaPropsFile = EUREKA_PROPS_FILE.get();
    try {
        ConfigurationManager.loadCascadedPropertiesFromResources(eurekaPropsFile);
    } catch (IOException e) {
        logger.warn(
                "Cannot find the properties specified : {}. This may be okay if there are other environment "
                        + "specific properties or the configuration is installed with a different mechanism.",
                eurekaPropsFile);

    }

    return configInstance;
}

看到上面代码想到了什么？这完全跟EurekaServerConfig创建的逻辑一样的呀，代码和DefaultEurekaServerConfig一致的逻辑。最后都是交给ConfigurationManager来管理。

EurekaClient创建过程

接着再来看eurekaClient = new DiscoveryClient(applicationInfoManager, eurekaClientConfig);代码：

这段代码确实很长，我们一段段来解读，解读完后再看代码：

1. 基于ApplicationInfoManager（包含了服务实例的信息、配置，作为服务实例管理的一个组件），eureka client相关的配置，一起构建了一个EurekaClient。

2. 这里有两个配置：config.shouldFetchRegistry()和config.shouldRegisterWithEureka()

   config.shouldFetchRegistry()：
   是否需要注册到别的注册中心。eurekaServer有个配置：eureka.client.fetchRegistry，单机情况下为false。false表示自己就是注册中心。我的职责就是维护服务实例，并不需要去检索服务

   config.shouldRegisterWithEureka()：
   是否要向别的注册中心注册自己。eurekaServer有个配置：eureka.client.registerWithEureka，单机情况下为false。false表示自己不需要向注册中心注册自己

3. 创建线程池调度任务
4. 创建一个心跳线程池
5. 创建一个缓存刷新线程池

6. 初始化线程调度任务

具体代码如下，添加了一些代码备注：

@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
                Provider<BackupRegistry> backupRegistryProvider) {
    if (args != null) {
        this.healthCheckHandlerProvider = args.healthCheckHandlerProvider;
        this.healthCheckCallbackProvider = args.healthCheckCallbackProvider;
        this.eventListeners.addAll(args.getEventListeners());
        this.preRegistrationHandler = args.preRegistrationHandler;
    } else {
        this.healthCheckCallbackProvider = null;
        this.healthCheckHandlerProvider = null;
        this.preRegistrationHandler = null;
    }

    this.applicationInfoManager = applicationInfoManager;
    InstanceInfo myInfo = applicationInfoManager.getInfo();

    clientConfig = config;
    staticClientConfig = clientConfig;
    transportConfig = config.getTransportConfig();
    instanceInfo = myInfo;
    if (myInfo != null) {
        // AppName是服务名称，instanceInfo.getId就是服务实例id，类似于：ServiceA/0001
        appPathIdentifier = instanceInfo.getAppName() + "/" + instanceInfo.getId();
    } else {
        logger.warn("Setting instanceInfo to a passed in null value");
    }

    this.backupRegistryProvider = backupRegistryProvider;

    this.urlRandomizer = new EndpointUtils.InstanceInfoBasedUrlRandomizer(instanceInfo);
    localRegionApps.set(new Applications());

    fetchRegistryGeneration = new AtomicLong(0);

    remoteRegionsToFetch = new AtomicReference<String>(clientConfig.fetchRegistryForRemoteRegions());
    remoteRegionsRef = new AtomicReference<>(remoteRegionsToFetch.get() == null ? null : remoteRegionsToFetch.get().split(","));

    // 是否需要注册到别的注册中心。eurekaServer有个配置：eureka.client.fetchRegistry，单机情况下为false。false表示自己就是注册中心。我的职责就是维护服务实例，并不需要去检索服务
    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;
    }
    // eurekaServer有个配置：eureka.client.registerWithEureka，单机情况下为false。false表示自己不需要向注册中心注册自己
    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());

    // 不需要注册也不需要抓取 释放不必要的资源
    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 {
        // default size of 2 - 1 each for heartbeat and cacheRefresh
        // 创建一个支持调度的线程池
        scheduler = Executors.newScheduledThreadPool(2,
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-%d")
                        .setDaemon(true)
                        .build());

        // 创建一个心跳检查的线程池，最大线程数为5
        heartbeatExecutor = new ThreadPoolExecutor(
                1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
                new SynchronousQueue<Runnable>(),
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
                        .setDaemon(true)
                        .build()
        );  // use direct handoff

        // 支持缓存刷新的线程池，最大线程数为5
        cacheRefreshExecutor = new ThreadPoolExecutor(
                1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
                new SynchronousQueue<Runnable>(),
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
                        .setDaemon(true)
                        .build()
        );  // use direct handoff

        // 支持底层的eureka client跟eureka server进行网络通信的组件
        eurekaTransport = new EurekaTransport();
        // 发送http请求，调用restful接口
        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);
    }

    // 如果要抓取注册表，但是抓取失败后，需要从备份中读取
    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();
    }
    // 初始化调度任务
    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);

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

/**
 * Initializes all scheduled tasks.
 */
private void initScheduledTasks() {
    // 抓取注册表的定时任务，
    if (clientConfig.shouldFetchRegistry()) {
        // registry cache refresh timer
        // registryFetchIntervalSeconds默认为30s
        int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
        int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
        // 执行cacheRefreshExecutor调度任务，默认是30s
        scheduler.schedule(
                new TimedSupervisorTask(
                        "cacheRefresh",
                        scheduler,
                        cacheRefreshExecutor,
                        registryFetchIntervalSeconds,
                        TimeUnit.SECONDS,
                        expBackOffBound,
                        new CacheRefreshThread()
                ),
                registryFetchIntervalSeconds, TimeUnit.SECONDS);
    }

    // 如果要将自己注册到其他注册中心
    if (clientConfig.shouldRegisterWithEureka()) {
        //  默认也是30s
        int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
        int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
        logger.info("Starting heartbeat executor: " + "renew interval is: " + renewalIntervalInSecs);

        // Heartbeat timer
        // 执行heartbeatExecutor心跳检查，默认是30s
        scheduler.schedule(
                new TimedSupervisorTask(
                        "heartbeat",
                        scheduler,
                        heartbeatExecutor,
                        renewalIntervalInSecs,
                        TimeUnit.SECONDS,
                        expBackOffBound,
                        new HeartbeatThread()
                ),
                renewalIntervalInSecs, TimeUnit.SECONDS);

        // InstanceInfo replicator
        // 创建服务副本传播器
        instanceInfoReplicator = new InstanceInfoReplicator(
                this,
                instanceInfo,
                clientConfig.getInstanceInfoReplicationIntervalSeconds(),
                2); // burstSize

        // 创建服务实例状态变更的监听器
        statusChangeListener = new ApplicationInfoManager.StatusChangeListener() {
            @Override
            public String getId() {
                return "statusChangeListener";
            }

            @Override
            public void notify(StatusChangeEvent statusChangeEvent) {
                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);
        }

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

总结

如果是eureka server的话，我们在玩儿spring cloud的时候，会将这个fetchRegistry给手动设置为false，如果是eureka server集群的话，就还是要保持为true。registerWithEureka也要设置为true。

（1）读取EurekaClientConfig，包括TransportConfig
（2）保存EurekaInstanceConfig和InstanceInfo
（3）处理了是否要注册以及抓取注册表，如果不要的话，释放一些资源
（4）支持调度的线程池
（5）支持心跳的线程池
（6）支持缓存刷新的线程池
（7）EurekaTransport，支持底层的eureka client跟eureka server进行网络通信的组件，对网络通信组件进行了一些初始化的操作
（8）如果要抓取注册表的话，在这里就会去抓取注册表了，但是如果说你配置了不抓取，那么这里就不抓取了
（9）初始化调度任务：如果要抓取注册表的话，就会注册一个定时任务，按照你设定的那个抓取的间隔，每隔一定时间（默认是30s），去执行一个CacheRefreshThread，给放那个调度线程池里去了；如果要向eureka server进行注册的话，会搞一个定时任务，每隔一定时间发送心跳，执行一个HeartbeatThread；创建了服务实例副本传播器，将自己作为一个定时任务进行调度；创建了服务实例的状态变更的监听器，如果你配置了监听，那么就会注册监听器

申明

本文章首发自本人博客：https://www.cnblogs.com/wang-meng 和公众号：壹枝花算不算浪漫，如若转载请标明来源!

感兴趣的小伙伴可关注个人公众号：壹枝花算不算浪漫