Eureka源码分析之eureka-client

最新推荐文章于 2024-09-02 01:03:39 发布

zhangyonggang123456

最新推荐文章于 2024-09-02 01:03:39 发布

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CC 4.0 BY-SA版权

分类专栏：源码分析文章标签： Eureka

本文链接：https://blog.youkuaiyun.com/zhangyonggang123456/article/details/80179136

很多人对Eureka进行了源码分析，但是主要着重于Eureka server端的源码分析，本篇博文着重分析eureka-client的分析，先上图看类结构（首先声明以下内容为本人浅显见解，如有不妥请指正批评）

eureka客户端核心jar包为以上截图，其中核心的类包为截图选中的com.netflix.discovery包。

com.netflix.discovery包主要解决Eureka注册中心实例对象的存储，刷新，续约等功能。其中还有一个自认为比较重要的包为

 
 com.netflix.discovery.shared.transport.decorator 

此包主要负责与eureka注册中心进行实际的请求交互操作。

通过上面的简单介绍下面从com.netflix.discovery开始着重介绍源码，主要解决以下疑惑：

（1）为什么注册中心宕机之后还能保持服务间调用（不要重启应用，下文会说）

com.netflix.discovery 这个包中最重要的类为DiscoveryClient

这个类中实现两个定时器，一个是续约，一个是刷新本地缓存的实例

类加载最终执行代@Inject注解的DiscoveryClient构造器方法，在这个方法中初始化两个定时任务线程池

 @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) {
            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(","));

        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;
        }

        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());

        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 {
            // 初始化两个线程的定时调度线程池
            scheduler = Executors.newScheduledThreadPool(2,
                    new ThreadFactoryBuilder()
                            .setNameFormat("DiscoveryClient-%d")
                            .setDaemon(true)
                            .build());
            // 心跳线