微服务组件--注册中心Spring Cloud Eureka分析

Eureka核心功能点

【1】服务注册(register)：Eureka Client会通过发送REST请求的方式向Eureka Server注册自己的服务，提供自身的元数据，比如ip地址、端口、运行状况指标的url、主页地址等信息。Eureka Server接收到注册请求后，就会把这些元数据信息存储在一个双层的Map中。

【2】服务续约(renew)：在服务注册后，Eureka Client会维护一个心跳来持续通知Eureka Server，说明服务一直处于可用状态，防止被剔除。Eureka Client在默认的情况下会每隔30秒(eureka.instance.leaseRenewalIntervalInSeconds)发送一次心跳来进行服务续约。

【3】服务同步(replicate)：Eureka Server之间会互相进行注册，构建Eureka Server集群，不同Eureka Server之间会进行服务同步，用来保证服务信息的一致性。

【4】获取服务(get registry)：服务消费者（Eureka Client）在启动的时候，会发送一个REST请求给Eureka Server，获取上面注册的服务清单，并且缓存在Eureka Client本地，默认缓存30秒(eureka.client.registryFetchIntervalSeconds)。同时，为了性能考虑，EurekaServer也会维护一份只读的服务清单缓存，该缓存每隔30秒更新一次。

【5】服务调用：服务消费者在获取到服务清单后，就可以根据清单中的服务列表信息，查找到其他服务的地址，从而进行远程调用。Eureka有Region和Zone的概念，一个Region可以包含多个Zone，在进行服务调用时，优先访问处于同一个Zone中的服务提供者。

【6】服务下线(cancel)：当Eureka Client需要关闭或重启时，就不希望在这个时间段内再有请求进来，所以，就需要提前先发送REST请求给Eureka Server，告诉Eureka Server自己要下线了，Eureka Server在收到请求后，就会把该服务状态置为下线（DOWN），并把该下线事件传播出去。

【7】服务剔除(evict)：有时候，服务实例可能会因为网络故障等原因导致不能提供服务，而此时该实例也没有发送请求给Eureka Server来进行服务下线，所以，还需要有服务剔除的机制。Eureka Server在启动的时候会创建一个定时任务，每隔一段时间（默认60秒），从当前服务清单中把超时没有续约（默认90秒，eureka.instance.leaseExpirationDurationInSeconds）的服务剔除。180s被剔除

【8】自我保护：既然Eureka Server会定时剔除超时没有续约的服务，那就有可能出现一种场景，网络一段时间内发生了异常，所有的服务都没能够进行续约，Eureka Server就把所有的服务都剔除了，这样显然不太合理。所以，就有了自我保护机制，当短时间内，统计续约失败的比例，如果达到一定阈值，则会触发自我保护的机制，在该机制下，Eureka Server不会剔除任何的微服务，等到正常后，再退出自我保护机制。自我保护开关(eureka.server.enable-self-preservation: false)

常见的问题

　　【1】当eureka服务实例有注册或下线或有实例发生故障，内存注册表虽然会及时更新数据，但是客户端不一定能及时感知到，可能会过30秒才能感知到，因为客户端拉取注册表实例这里面有一个多级缓存机制。【实现的是最终一致性】

　　【2】还有服务剔除的不是默认90秒没心跳的实例，剔除的是180秒没心跳的实例(eureka的bug导致，注解有说明是因为加了两次过期时间，但是很小的BUG所有不修复了【在Lease结构里说明】）

源码精髓总结

【1】服务端多级缓存设计思想：

　　1）在拉取注册表的时候：

　　　　（1）首先从ReadOnlyCacheMap里查缓存的注册表。

　　　　（2）若没有，就找ReadWriteCacheMap里缓存的注册表。

　　　　（3）如果还没有，就从内存中获取实际的注册表数据。

　　2）在注册表发生变更的时候：

　　　　（1）会在内存中更新变更的注册表数据，同时过期掉ReadWriteCacheMap。

　　　　（2）此过程不会影响ReadOnlyCacheMap提供人家查询注册表。

　　　　（3）默认每30秒Eureka Server会将ReadWriteCacheMap更新到ReadOnlyCacheMap里

　　　　（4）默认每180秒Eureka Server会将ReadWriteCacheMap里是数据失效

　　　　（5）下次有服务拉取注册表，又会从内存中获取最新的数据了，同时填充 各级缓存

　　3）多级缓存机制的优点：

　　　　（1）尽可能保证了内存注册表数据不会出现频繁的读写冲突问题。

　　　　（2）并且进一步保证对Eureka Server的大量请求，都是快速从纯内存走，性能极高（可以稍微估计下对于一线互联网公司，内部上千个eureka client实例，每分钟对eureka大几千次的访问，一天就是上千万次的访问）

【2】TimedSupervisorTask定时任务的设计：

　　1）从整体上看，TimedSupervisorTask是固定间隔的周期性任务，一旦遇到超时就会将下一个周期的间隔时间调大，如果连续超时，那么每次间隔时间都会增大一倍，一直到达外部参数设定的上限为止，一旦新任务不再超时，间隔时间又会自动恢复为初始值，另外还有CAS来控制多线程同步。

【3】增量更新中哈希码检验的设计：

//里面的一致性哈希码，本质上就是校验数据
//如：服务器上全量块存的是【ABCDEFG】,此时它的哈希码便是全量块存的数据的哈希值,增量块存的是【FG】，
//而我们客户端是【ABCD】，增量拉下来再合并，则为【ABCDFG】，得到的哈希值便会与全量哈希值不一致，代表了缺失一部分数据
//故检验不对就会全量拉取

【4】注册表的结构说明（这个仅是记录）：

实例信息存放的map，这是个两层的ConcurrentHashMap<String, Map<String,Lease<InstanceInfo>>>，外层map的key是appName，也就是服务名，内层map的key是instanceId，也就是实例名
注册表map数据示例如下：
{
    MICROSERVICE - PROVIDER - USER = {
        DESKTOP - 1 SLJLB7: microservice - provider - user: 8002 = com.netflix.eureka.lease.Lease @2cd36af6,
        DESKTOP - 1 SLJLB7: microservice - provider - user: 8001 = com.netflix.eureka.lease.Lease @600b7073
    }，
    MICROSERVICE - PROVIDER - ORDER = {
        DESKTOP - 1 SLJLB7: microservice - provider - order: 8002 = com.netflix.eureka.lease.Lease @2cd36af6,
        DESKTOP - 1 SLJLB7: microservice - provider - order: 8001 = com.netflix.eureka.lease.Lease @600b7073
    }
}

Eureka服务端源码分析

【1】分析注解@EnableEurekaServer是如何开启eurekaServer服务注册功能

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(EurekaServerMarkerConfiguration.class)
public @interface EnableEurekaServer {}

//注释有说：这个注解是为了激活Eureka相关的配置类EurekaServerAutoConfiguration类
//但是却是导入了EurekaServerMarkerConfiguration类

【2】分析导入的EurekaServerMarkerConfiguration类

//注释说明：采用Marker的bean去激活EurekaServerAutoConfiguration类
//但实际上并没有做什么，直接去EurekaServerAutoConfiguration类看他是怎么处理的
@Configuration(proxyBeanMethods = false)
public class EurekaServerMarkerConfiguration {
    @Bean
    public Marker eurekaServerMarkerBean() {
        return new Marker();
    }

    class Marker {}
}

【3】分析EurekaServerAutoConfiguration类

@Configuration(proxyBeanMethods = false)
@Import(EurekaServerInitializerConfiguration.class)
//当发现了这里，便明白了，这个配置类要生效是必须要有Marker类的存在
//而且EurekaServerAutoConfiguration类本身是基于SpringBoot的SPI机制，自动导入的
@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)
@EnableConfigurationProperties({ EurekaDashboardProperties.class,InstanceRegistryProperties.class })
@PropertySource("classpath:/eureka/server.properties")
public class EurekaServerAutoConfiguration implements WebMvcConfigurer {...}

【4】分析EurekaServerAutoConfiguration类中的方法

//初始化集群节点集合
@Bean
@ConditionalOnMissingBean
public PeerEurekaNodes peerEurekaNodes(PeerAwareInstanceRegistry registry, ServerCodecs serverCodecs, ReplicationClientAdditionalFilters replicationClientAdditionalFilters) {
    return new RefreshablePeerEurekaNodes(registry, this.eurekaServerConfig,
            this.eurekaClientConfig, serverCodecs, this.applicationInfoManager,
            replicationClientAdditionalFilters);
}

//初始化EurekaServer的相关配置
@Configuration(proxyBeanMethods = false)
protected static class EurekaServerConfigBeanConfiguration {
    @Bean
    @ConditionalOnMissingBean
    public EurekaServerConfig eurekaServerConfig(EurekaClientConfig clientConfig) {
        EurekaServerConfigBean server = new EurekaServerConfigBean();
        if (clientConfig.shouldRegisterWithEureka()) {
            // Set a sensible default if we are supposed to replicate
            server.setRegistrySyncRetries(5);
        }
        return server;
    }
}

//初始化一些接口，用于获取EurekaServer的信息
@Bean
@ConditionalOnProperty(prefix = "eureka.dashboard", name = "enabled", matchIfMissing = true)
public EurekaController eurekaController() {
    return new EurekaController(this.applicationInfoManager);
}

//基于EurekaServer的配置，注册表，集群节点集合，以及服务实例初始化EurekaServer上下文
@Bean
public EurekaServerContext eurekaServerContext(ServerCodecs serverCodecs, PeerAwareInstanceRegistry registry, PeerEurekaNodes peerEurekaNodes) {
    return new DefaultEurekaServerContext(this.eurekaServerConfig, serverCodecs, registry, peerEurekaNodes, this.applicationInfoManager);
}

//初始化经过包装的Eureka原生启动类
@Bean
public EurekaServerBootstrap eurekaServerBootstrap(PeerAwareInstanceRegistry registry, EurekaServerContext serverContext) {
    return new EurekaServerBootstrap(this.applicationInfoManager,
            this.eurekaClientConfig, this.eurekaServerConfig, registry,
            serverContext);
}

//初始化集群注册表
@Bean
public PeerAwareInstanceRegistry peerAwareInstanceRegistry(ServerCodecs serverCodecs) {
    this.eurekaClient.getApplications(); // force initialization
    return new InstanceRegistry(this.eurekaServerConfig, this.eurekaClientConfig,
            serverCodecs, this.eurekaClient,
            this.instanceRegistryProperties.getExpectedNumberOfClientsSendingRenews(),
            this.instanceRegistryProperties.getDefaultOpenForTrafficCount());
}

【5】分析EurekaServerAutoConfiguration类导入的EurekaServerInitializerConfiguration类

//因为实现了SmartLifecycle接口，会在初始化完成后根据isAutoStartup()的返回值确认是否调用start()方法
//故查看EurekaServerInitializerConfiguration类#start()方法
@Override
public void start() {
    new Thread(() -> {
        try {
            //初始化EurekaServer，同时启动Eureka Server
            eurekaServerBootstrap.contextInitialized(EurekaServerInitializerConfiguration.this.servletContext);
            log.info("Started Eureka Server");
            //发送Eureka注册事件
            publish(new EurekaRegistryAvailableEvent(getEurekaServerConfig()));
            // 设置启动的状态为true
            EurekaServerInitializerConfiguration.this.running = true;
            // 发送Eureka Start事件，其他还有各种事件，我们可以监听这种时间，然后做一些特定的业务需求
            publish(new EurekaServerStartedEvent(getEurekaServerConfig()));
        }
        catch (Exception ex) {...}
    }).start();
}

//初始化EurekaServer的运行环境和上下文
//EurekaServerBootstrap类#contextInitialized方法
public void contextInitialized(ServletContext context) {
    try {
        //初始化运行环境
        initEurekaEnvironment();
        //初始化上下文
        initEurekaServerContext();

        context.setAttribute(EurekaServerContext.class.getName(), this.serverContext);
    }
    catch (Throwable e) {
        throw new RuntimeException(...);
    }
}

【6】分析初始化上下文initEurekaServerContext方法做了什么【进行了服务同步，服务剔除的启动】

protected void initEurekaServerContext() throws Exception {
    // For backward compatibility
    JsonXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(),
            XStream.PRIORITY_VERY_HIGH);
    XmlXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(),
            XStream.PRIORITY_VERY_HIGH);

    if (isAws(this.applicationInfoManager.getInfo())) {
        this.awsBinder = new AwsBinderDelegate(this.eurekaServerConfig,
                this.eurekaClientConfig, this.registry, this.applicationInfoManager);
        this.awsBinder.start();
    }
    //初始化eureka server上下文
    EurekaServerContextHolder.initialize(this.serverContext);

    log.info("Initialized server context");

    // Copy registry from neighboring eureka node
    // 从相邻的eureka节点复制注册表
    int registryCount = this.registry.syncUp();
    // 默认每30秒发送心跳，1分钟就是2次
    // 修改eureka状态为up
    // 同时，这里面会开启一个定时任务，用于清理60秒没有心跳的客户端。自动下线
    // 根据属性值可知是PeerAwareInstanceRegistry类
    this.registry.openForTraffic(this.applicationInfoManager, registryCount);

    // Register all monitoring statistics.
    EurekaMonitors.registerAllStats();
}

//返回了一个EurekaServerContextHolder【其实就是将serverContext设置进入到里面当做属性值】
public static synchronized void initialize(EurekaServerContext serverContext) {
    holder = new EurekaServerContextHolder(serverContext);
}

【7】服务同步的逻辑

//进行服务同步
@Override
public int syncUp() {
    // Copy entire entry from neighboring DS node
    int count = 0;
    //从配置文件中拿到注册的节点
    for (int i = 0; ((i < serverConfig.getRegistrySyncRetries()) && (count == 0)); i++) {
        if (i > 0) {
            try {
                Thread.sleep(serverConfig.getRegistrySyncRetryWaitMs());
            } catch (InterruptedException e) { break; }
        }
        //调用节点的http请求获取所有的服务实例
        Applications apps = eurekaClient.getApplications();
        for (Application app : apps.getRegisteredApplications()) {
            for (InstanceInfo instance : app.getInstances()) {
                try {
                    if (isRegisterable(instance)) {
                        //将其他节点的实例注册到本节点
                        register(instance, instance.getLeaseInfo().getDurationInSecs(), true);
                        count++;
                    }
                } catch (Throwable t) {...}
            }
        }
    }
    return count;
}

【8】服务剔除的逻辑

//进行服务剔除
@Override
public void openForTraffic(ApplicationInfoManager applicationInfoManager, int count) {
    // Renewals happen every 30 seconds and for a minute it should be a factor of 2.
    // 计算每分钟最大续约数
    this.expectedNumberOfClientsSendingRenews = count;
    // 每分钟最小续约数
    updateRenewsPerMinThreshold();

    this.startupTime = System.currentTimeMillis();
    if (count > 0) {
        this.peerInstancesTransferEmptyOnStartup = false;
    }
    DataCenterInfo.Name selfName = applicationInfoManager.getInfo().getDataCenterInfo().getName();
    boolean isAws = Name.Amazon == selfName;
    if (isAws && serverConfig.shouldPrimeAwsReplicaConnections()) {
        primeAwsReplicas(applicationInfoManager);
    }
    logger.info("Changing status to UP");
    // 设置实例的状态为UP
    applicationInfoManager.setInstanceStatus(InstanceStatus.UP);
    // 开启定时任务，默认60秒执行一次，用于清理60秒之内没有续约的实例
    super.postInit();
}

protected void updateRenewsPerMinThreshold() {
    this.numberOfRenewsPerMinThreshold = (int) (this.expectedNumberOfClientsSendingRenews
            * (60.0 / serverConfig.getExpectedClientRenewalIntervalSeconds())
            * serverConfig.getRenewalPercentThreshold());
}

protected void postInit() {
    renewsLastMin.start();
    if (evictionTaskRef.get() != null) {
        evictionTaskRef.get().cancel();
    }
    evictionTaskRef.set(new EvictionTask());
    //服务剔除任务
    //evictionIntervalTimerInMs = 60 * 1000，即每60s执行一次，且延迟60s
    evictionTimer.schedule(evictionTaskRef.get(),
            serverConfig.getEvictionIntervalTimerInMs(),
            serverConfig.getEvictionIntervalTimerInMs());
}
//EvictionTask类#run方法
@Override
public void run() {
    try {
        long compensationTimeMs = getCompensationTimeMs();
        logger.info("Running the evict task with compensationTime {}ms", compensationTimeMs);
        evict(compensationTimeMs);
    } catch (Throwable e) {...}
}

//剔除逻辑
public void evict(long additionalLeaseMs) {
    logger.debug("Running the evict task");

    if (!isLeaseExpirationEnabled()) {
        logger.debug("DS: lease expiration is currently disabled.");
        return;
    }

    // We collect first all expired items, to evict them in random order. For large eviction sets,
    // if we do not that, we might wipe out whole apps before self preservation kicks in. By randomizing it,
    // the impact should be evenly distributed across all applications.
    List<Lease<InstanceInfo>> expiredLeases = new ArrayList<>();
    for (Entry<String, Map<String, Lease<InstanceInfo>>> groupEntry : registry.entrySet()) {
        Map<String, Lease<InstanceInfo>> leaseMap = groupEntry.getValue();
        if (leaseMap != null) {
            for (Entry<String, Lease<InstanceInfo>> leaseEntry : leaseMap.entrySet()) {
                Lease<InstanceInfo> lease = leaseEntry.getValue();
                if (lease.isExpired(additionalLeaseMs) && lease.getHolder() != null) {
                    expiredLeases.add(lease);
                }
            }
        }
    }

    // To compensate for GC pauses or drifting local time, we need to use current registry size as a base for
    // triggering self-preservation. Without that we would wipe out full registry.
    int registrySize = (int) getLocalRegistrySize();
    int registrySizeThreshold = (int) (registrySize * serverConfig.getRenewalPercentThreshold());
    int evictionLimit = registrySize - registrySizeThreshold;

    int toEvict = Math.min(expiredLeases.size(), evictionLimit);
    if (toEvict > 0) {
        logger.info("Evicting {} items (expired={}, evictionLimit={})", toEvict, expiredLeases.size(), evictionLimit);

        Random random = new Random(System.currentTimeMillis());
        for (int i = 0; i < toEvict; i++) {
            // Pick a random item (Knuth shuffle algorithm)
            int next = i + random.nextInt(expiredLeases.size() - i);
            Collections.swap(expiredLeases, i, next);
            Lease<InstanceInfo> lease = expiredLeases.get(i);

            String appName = lease.getHolder().getAppName();
            String id = lease.getHolder().getId();
            EXPIRED.increment();
            logger.warn("DS: Registry: expired lease for {}/{}", appName, id);
            internalCancel(appName, id, false);
        }
    }
}

Eureka客户端源码分析

【1】根据SpringBoot自动装配先找出所有会调用的类

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.cloud.netflix.eureka.config.EurekaClientConfigServerAutoConfiguration,\
org.springframework.cloud.netflix.eureka.config.EurekaDiscoveryClientConfigServiceAutoConfiguration,\
org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration,\
org.springframework.cloud.netflix.ribbon.eureka.RibbonEurekaAutoConfiguration,\
org.springframework.cloud.netflix.eureka.EurekaDiscoveryClientConfiguration,\
org.springframework.cloud.netflix.eureka.reactive.EurekaReactiveDiscoveryClientConfiguration,\
org.springframework.cloud.netflix.eureka.loadbalancer.LoadBalancerEurekaAutoConfiguration

org.springframework.cloud.bootstrap.BootstrapConfiguration=\
org.springframework.cloud.netflix.eureka.config.EurekaDiscoveryClientConfigServiceBootstrapConfiguration

【2】找到对应的自动装配类EurekaClientAutoConfiguration类

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties
@ConditionalOnClass(EurekaClientConfig.class)
@Import(DiscoveryClientOptionalArgsConfiguration.class)
@ConditionalOnProperty(value = "eureka.client.enabled", matchIfMissing = true)
@ConditionalOnDiscoveryEnabled
@AutoConfigureBefore({ NoopDiscoveryClientAutoConfiguration.class,
        CommonsClientAutoConfiguration.class, ServiceRegistryAutoConfiguration.class })
@AutoConfigureAfter(name = {
        "org.springframework.cloud.autoconfigure.RefreshAutoConfiguration",
        "org.springframework.cloud.netflix.eureka.EurekaDiscoveryClientConfiguration",
        "org.springframework.cloud.client.serviceregistry.AutoServiceRegistrationAutoConfiguration" })
public class EurekaClientAutoConfiguration {
    //初始化EurekaClient的相关配置
    @Bean
    @ConditionalOnMissingBean(value = EurekaClientConfig.class,
            search = SearchStrategy.CURRENT)
    public EurekaClientConfigBean eurekaClientConfigBean(ConfigurableEnvironment env) {
        EurekaClientConfigBean client = new EurekaClientConfigBean();
        if ("bootstrap".equals(this.env.getProperty("spring.config.name"))) {
            // We don't register during bootstrap by default, but there will be another
            // chance later.
            client.setRegisterWithEureka(false);
        }
        return client;
    }

    //Client启动时的自动注册Bean
    @Bean
    @ConditionalOnBean(AutoServiceRegistrationProperties.class)
    @ConditionalOnProperty(value = "spring.cloud.service-registry.auto-registration.enabled", matchIfMissing = true)
    public EurekaAutoServiceRegistration eurekaAutoServiceRegistration(
            ApplicationContext context, EurekaServiceRegistry registry,
            EurekaRegistration registration) {
        return new EurekaAutoServiceRegistration(context, registry, registration);
    }

    //EurekaClient配置类
    @Configuration(proxyBeanMethods = false)
    @ConditionalOnMissingRefreshScope
    protected static class EurekaClientConfiguration {

        @Autowired
        private ApplicationContext context;

        @Autowired
        private AbstractDiscoveryClientOptionalArgs<?> optionalArgs;

        @Bean(destroyMethod = "shutdown")
        @ConditionalOnMissingBean(value = EurekaClient.class,search = SearchStrategy.CURRENT)
        public EurekaClient eurekaClient(ApplicationInfoManager manager, EurekaClientConfig config) {
            return new CloudEurekaClient(manager, config, this.optionalArgs, this.context);
        }

        @Bean
        @ConditionalOnMissingBean(value = ApplicationInfoManager.class, search = SearchStrategy.CURRENT)
        public ApplicationInfoManager eurekaApplicationInfoManager(EurekaInstanceConfig config) {
            InstanceInfo instanceInfo = new InstanceInfoFactory().create(config);
            return new ApplicationInfoManager(config, instanceInfo);
        }

        @Bean
        @ConditionalOnBean(AutoServiceRegistrationProperties.class)
        @ConditionalOnProperty(value = "spring.cloud.service-registry.auto-registration.enabled", matchIfMissing = true)
        public EurekaRegistration eurekaRegistration(EurekaClient eurekaClient, CloudEurekaInstanceConfig instanceConfig, ApplicationInfoManager applicationInfoManager, @Autowired( required = false) ObjectProvider<HealthCheckHandler> healthCheckHandler) {
            return EurekaRegistration.builder(instanceConfig).with(applicationInfoManager)
                    .with(eurekaClient).with(healthCheckHandler).build();
        }

    }
....
}

【2.1】分析注解@AutoConfigureAfter导入的EurekaDiscoveryClientConfiguration类做了什么

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties
@ConditionalOnClass(EurekaClientConfig.class)
@ConditionalOnProperty(value = "eureka.client.enabled", matchIfMissing = true)
@ConditionalOnDiscoveryEnabled
@ConditionalOnBlockingDiscoveryEnabled
public class EurekaDiscoveryClientConfiguration {

    //基于EurekaClientAutoConfiguration的启动标志
    @Deprecated
    @Bean
    public Marker eurekaDiscoverClientMarker() {
        return new Marker();
    }

    //将EurekaClient包装成EurekaDiscoveryClient
    @Bean
    @ConditionalOnMissingBean
    public EurekaDiscoveryClient discoveryClient(EurekaClient client,
            EurekaClientConfig clientConfig) {
        return new EurekaDiscoveryClient(client, clientConfig);
    }

    //心跳检测的处理配置
    @Configuration(proxyBeanMethods = false)
    @ConditionalOnProperty(value = "eureka.client.healthcheck.enabled",matchIfMissing = false)
    protected static class EurekaHealthCheckHandlerConfiguration {

        @Autowired(required = false)
        private StatusAggregator statusAggregator = new SimpleStatusAggregator();

        @Bean
        @ConditionalOnMissingBean(HealthCheckHandler.class)
        public EurekaHealthCheckHandler eurekaHealthCheckHandler() {
            return new EurekaHealthCheckHandler(this.statusAggregator);
        }

    }

    @Deprecated
    class Marker {

    }

    //定义了Client配置重刷的监听器
    @Configuration(proxyBeanMethods = false)
    @ConditionalOnClass(RefreshScopeRefreshedEvent.class)
    protected static class EurekaClientConfigurationRefresher implements ApplicationListener<RefreshScopeRefreshedEvent> {
        ....
    }

}

//看得出来包装也只是将配置和客户端放在了一起
public EurekaDiscoveryClient(EurekaClient eurekaClient,
        EurekaClientConfig clientConfig) {
    this.clientConfig = clientConfig;
    this.eurekaClient = eurekaClient;
}

【3】分析EurekaClient的相关配置EurekaClientConfigBean类

//仅列举了部分
@ConfigurationProperties(EurekaClientConfigBean.PREFIX)
public class EurekaClientConfigBean implements EurekaClientConfig, Ordered {
    //客户端配置前缀
    public static final String PREFIX = "eureka.client";
    //public static final String DEFAULT_PREFIX = "/eureka";
    //默认的注册地址
    public static final String DEFAULT_URL = "http://localhost:8761" + DEFAULT_PREFIX + "/";
    //默认域
    public static final String DEFAULT_ZONE = "defaultZone";

    private static final int MINUTES = 60;

    //多长时间从注册中心服务端拉取一次服务信息，单位秒；这个就是主动拉取注册中心上所有服务的实例信息
    private int registryFetchIntervalSeconds = 30;
    //多长时间复制实例变化到eureka服务端，单位秒；这个配置是复制实例信息到注册中心
    private int instanceInfoReplicationIntervalSeconds = 30;
    //实例初始化复制信息到eureka服务端的间隔时间，所以可以看到，其实实例的初始化阶段不是立即复制实例信息到注册中心的，单位秒
    private int initialInstanceInfoReplicationIntervalSeconds = 40;
    //eureka服务端的变化，多长时间，客户端会获取一次eureka服务的信息
    private int eurekaServiceUrlPollIntervalSeconds = 5 * MINUTES;
    //eureka server的代理端口
    private String proxyPort;
    //eureka server的代理host name
    private String proxyHost;
    //账号
    private String proxyUserName;
    //密码
    private String proxyPassword;
    //从server读取所需的超时时间
    private int eurekaServerReadTimeoutSeconds = 8;
    //连接server的超时时间
    private int eurekaServerConnectTimeoutSeconds = 5;
    //被允许连接到所有server host的总连接数
    private int eurekaServerTotalConnections = 200;
    // 被允许连接到每一个server host的总连接数
    private int eurekaServerTotalConnectionsPerHost = 50;
    //连接到server的http连接的空闲超时时间，超时会被清理掉
    private int eurekaConnectionIdleTimeoutSeconds = 30;
    //heartbeatExecutor 心跳的线程数
    private int heartbeatExecutorThreadPoolSize = 2;
    //客户端初始化阶段强制注册，默认关闭
    private boolean shouldEnforceRegistrationAtInit = false;

...
}

【4】分析EurekaClientConfiguration配置类里面生成的EurekaClient的Bean

//CloudEurekaClient类【继承DiscoveryClient类】#构造方法
public CloudEurekaClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs<?> args, ApplicationEventPublisher publisher) {
    super(applicationInfoManager, config, args);
    this.applicationInfoManager = applicationInfoManager;
    this.publisher = publisher;
    this.eurekaTransportField = ReflectionUtils.findField(DiscoveryClient.class,
            "eurekaTransport");
    ReflectionUtils.makeAccessible(this.eurekaTransportField);
}

//DiscoveryClient类【继承EurekaClient（原生的EurekaClient）】#构造方法
public DiscoveryClient(ApplicationInfoManager applicationInfoManager, final EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args) {
    this(applicationInfoManager, config, args, ResolverUtils::randomize);
}

public DiscoveryClient(ApplicationInfoManager applicationInfoManager, final EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args, EndpointRandomizer randomizer) {
    //主要是这个this指向，毕竟里面的都是方法传参
    this(applicationInfoManager, config, args, new Provider<BackupRegistry>() {
        private volatile BackupRegistry backupRegistryInstance;

        @Override
        public synchronized BackupRegistry get() {
            if (backupRegistryInstance == null) {
                String backupRegistryClassName = config.getBackupRegistryImpl();
                if (null != backupRegistryClassName) {
                    try {
                        backupRegistryInstance = (BackupRegistry) Class.forName(backupRegistryClassName).newInstance();
                        logger.info("Enabled backup registry of type {}", backupRegistryInstance.getClass());
                    } catch (InstantiationException e) {..} catch (IllegalAccessException e) {..} catch (ClassNotFoundException e) {...}
                }

                if (backupRegistryInstance == null) {
                    logger.warn("Using default backup registry implementation which does not do anything.");
                    backupRegistryInstance = new NotImplementedRegistryImpl();
                }
            }

            return backupRegistryInstance;
        }
    }, randomizer);
}

【5】分析DiscoveryClient的构造方法

@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args, Provider<BackupRegistry> backupRegistryProvider, EndpointRandomizer endpointRandomizer) {
    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 {...}

    this.backupRegistryProvider = backupRegistryProvider;
    this.endpointRandomizer = endpointRandomizer;
    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;
    }

    //从这里开始初始化Eureka Client
    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
        scheduler = Executors.newScheduledThreadPool(2,
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-%d")
                        .setDaemon(true)
                        .build());
        //心跳的线程池
        heartbeatExecutor = new ThreadPoolExecutor(
                1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
                new SynchronousQueue<Runnable>(),
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
                        .setDaemon(true)
                        .build()
        );  // use direct handoff
        //缓存重刷的线程池
        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);
    }

    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();
    }

    if (clientConfig.shouldRegisterWithEureka() && clientConfig.shouldEnforceRegistrationAtInit()) {
        try {
            if (!register() ) {
                throw new IllegalStateException("Registration error at startup. Invalid server response.");
            }
        } catch (Throwable th) {...}
    }

    // finally, init the schedule tasks (e.g. cluster resolvers, heartbeat, instanceInfo replicator, fetch
    //最核心代码，初始化定时任务
    initScheduledTasks();

    try {
        Monitors.registerObject(this);
    } catch (Throwable e) {...}

    DiscoveryManager.getInstance().setDiscoveryClient(this);
    DiscoveryManager.getInstance().setEurekaClientConfig(config);

    initTimestampMs = System.currentTimeMillis();
}

【6】核心逻辑initScheduledTasks初始化定时任务，是做了什么

/**
 * Initializes all scheduled tasks.
 */
private void initScheduledTasks() {
    //获取服务注册列表信息
    if (clientConfig.shouldFetchRegistry()) {
        //服务注册列表更新的周期时间
        //默认是30
        int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
        int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
        //定时更新服务注册列表
        //这里的延时任务明显是只调用一次，具体在分析他的任务的run方法
        scheduler.schedule(
                new TimedSupervisorTask(
                        "cacheRefresh",
                        scheduler,
                        cacheRefreshExecutor,
                        registryFetchIntervalSeconds,
                        TimeUnit.SECONDS,
                        expBackOffBound,
                        new CacheRefreshThread()   //该线程执行更新的具体逻辑
                ),
                registryFetchIntervalSeconds, TimeUnit.SECONDS);
    }

    if (clientConfig.shouldRegisterWithEureka()) {
        //服务续约的周期时间
        int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
        int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
        //应用启动可见此日志，内容是：Starting heartbeat executor: renew interval is: 30
        logger.info("Starting heartbeat executor: " + "renew interval is: {}", renewalIntervalInSecs);

        // Heartbeat timer
        // 服务定时续约
        scheduler.schedule(
                new TimedSupervisorTask(
                        "heartbeat",
                        scheduler,
                        heartbeatExecutor,
                        renewalIntervalInSecs,
                        TimeUnit.SECONDS,
                        expBackOffBound,
                        new HeartbeatThread()  //该线程执行续约的具体逻辑
                ),
                renewalIntervalInSecs, TimeUnit.SECONDS);

        //这个Runable中含有服务注册的逻辑
        instanceInfoReplicator = new InstanceInfoReplicator(
                this,
                instanceInfo,
                clientConfig.getInstanceInfoReplicationIntervalSeconds(),
                2); // burstSize

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

【6.1】定时任务TimedSupervisorTask类的设计

//TimedSupervisorTask类#run方法
//这里存在一个设计的亮点
public class TimedSupervisorTask extends TimerTask {
    ...

    public TimedSupervisorTask(String name, ScheduledExecutorService scheduler, ThreadPoolExecutor executor,
                               int timeout, TimeUnit timeUnit, int expBackOffBound, Runnable task) {
        this.scheduler = scheduler;
        this.executor = executor;
        this.timeoutMillis = timeUnit.toMillis(timeout);
        this.task = task;  //可以看出任务还是需要根据传入来的
        this.delay = new AtomicLong(timeoutMillis);
        this.maxDelay = timeoutMillis * expBackOffBound;
        // Initialize the counters and register.
        successCounter = Monitors.newCounter("success");
        timeoutCounter = Monitors.newCounter("timeouts");
        rejectedCounter = Monitors.newCounter("rejectedExecutions");
        throwableCounter = Monitors.newCounter("throwables");
        threadPoolLevelGauge = new LongGauge(MonitorConfig.builder("threadPoolUsed").build());
        Monitors.registerObject(name, this);
    }

    @Override
    public void run() {
        Future<?> future = null;
        try {
            future = executor.submit(task);
            threadPoolLevelGauge.set((long) executor.getActiveCount());
            //设置了超时时间
            future.get(timeoutMillis, TimeUnit.MILLISECONDS);  // block until done or timeout
            //出现任务不超时的情况又会将延迟时间重置（这里主要是配合下面捕捉异常的超时翻倍情况）
            delay.set(timeoutMillis);
            threadPoolLevelGauge.set((long) executor.getActiveCount());
            successCounter.increment();
        } catch (TimeoutException e) {
            logger.warn("task supervisor timed out", e);
            //出现超时的记录
            timeoutCounter.increment();
            //将超时时间翻倍（在最大的任务时间内），主动延迟
            long currentDelay = delay.get();
            long newDelay = Math.min(maxDelay, currentDelay * 2);
            //设置为最新的值，考虑到多线程，所以用了CAS
            delay.compareAndSet(currentDelay, newDelay);

        } catch (RejectedExecutionException e) {
            //一旦线程池的阻塞队列中放满了待处理任务，触发了拒绝策略，就会将调度器停掉
            if (executor.isShutdown() || scheduler.isShutdown()) {
                logger.warn("task supervisor shutting down, reject the task", e);
            } else {
                logger.warn("task supervisor rejected the task", e);
            }
            //被拒绝的次数
            rejectedCounter.increment();
        } catch (Throwable e) {
            if (executor.isShutdown() || scheduler.isShutdown()) {
                logger.warn("task supervisor shutting down, can't accept the task");
            } else {
                logger.warn("task supervisor threw an exception", e);
            }

            throwableCounter.increment();
        } finally {
            if (future != null) {
                //这里任务要么执行完毕，要么发生异常，都用cancel方法来清理任务；
                future.cancel(true);
            }
            //只要调度器没有停止，就再指定等待时间之后在执行一次同样的任务
            //任务里面又塞入这个任务
            if (!scheduler.isShutdown()) {
                //假设外部调用时传入的超时时间为30秒（构造方法的入参timeout），最大间隔时间为50秒(构造方法的入参expBackOffBound)
                //如果最近一次任务没有超时，那么就在30秒后开始新任务，
                //如果最近一次任务超时了，那么就在50秒后开始新任务（异常处理中有个乘以二的操作，乘以二后的60秒超过了最大间隔50秒）
                scheduler.schedule(this, delay.get(), TimeUnit.MILLISECONDS);
            }
        }
    }
}

【6.2】分析更新服务注册列表任务 CacheRefreshThread【获取服务逻辑】

//DiscoveryClient类的内置类
class CacheRefreshThread implements Runnable {
    public void run() {
        refreshRegistry();
    }
}

//DiscoveryClient类#refreshRegistry方法
@VisibleForTesting
void refreshRegistry() {
    try {
        boolean isFetchingRemoteRegionRegistries = isFetchingRemoteRegionRegistries();

        boolean remoteRegionsModified = false;
        // This makes sure that a dynamic change to remote regions to fetch is honored.
        String latestRemoteRegions = clientConfig.fetchRegistryForRemoteRegions();
        //不做aws环境的配置这个if逻辑不会执行
        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 {....}
                }
            } else {
                // Just refresh mapping to reflect any DNS/Property change
                instanceRegionChecker.getAzToRegionMapper().refreshMapping();
            }
        }
        //获取注册信息方法
        boolean success = fetchRegistry(remoteRegionsModified);
        if (success) {
            registrySize = localRegionApps.get().size();
            lastSuccessfulRegistryFetchTimestamp = System.currentTimeMillis();
        }

        if (logger.isDebugEnabled()) {...省略日志内容...}
    } catch (Throwable e) {...}
}

private boolean fetchRegistry(boolean forceFullRegistryFetch) {
    Stopwatch tracer = FETCH_REGISTRY_TIMER.start();

    try {
        // 如果增量被禁用，或者是第一次，那么获取所有应用程序
        // 取出本地缓存之前获取的服务列表信息
        Applications applications = getApplications();
        //是否禁用增量更新
        if (clientConfig.shouldDisableDelta()
                || (!Strings.isNullOrEmpty(clientConfig.getRegistryRefreshSingleVipAddress()))
                || forceFullRegistryFetch
                //是否第一次拉取
                || (applications == null)
                || (applications.getRegisteredApplications().size() == 0)
                || (applications.getVersion() == -1)) //Client application does not have latest library supporting delta
        {
            //全量获取
            getAndStoreFullRegistry();
        } else {
            //增量获取
            getAndUpdateDelta(applications);
        }
        //更新本地缓存
        applications.setAppsHashCode(applications.getReconcileHashCode());
        logTotalInstances();
    } catch (Throwable e) {
        return false;
    } finally {
        if (tracer != null) {
            tracer.stop();
        }
    }

    // Notify about cache refresh before updating the instance remote status
    //将本地缓存更新的事件广播给所有已注册的监听器，注意该方法已被CloudEurekaClient类重写
    onCacheRefreshed();
    // Update remote status based on refreshed data held in the cache
    //检查刚刚更新的缓存中，有来自Eureka server的服务列表，其中包含了当前应用的状态，
    //当前实例的成员变量lastRemoteInstanceStatus，记录的是最后一次更新的当前应用状态，
    //上述两种状态在updateInstanceRemoteStatus方法中作比较 ，如果不一致，就更新lastRemoteInstanceStatus，并且广播对应的事件
    updateInstanceRemoteStatus();
    // registry was fetched successfully, so return true
    return true;
}

@Override
public Applications getApplications() {
    return localRegionApps.get();
}

【6.2.1】分析全量更新

private void getAndStoreFullRegistry() throws Throwable {
    long currentUpdateGeneration = fetchRegistryGeneration.get();

    Applications apps = null;
    //由于并没有配置特别关注的region信息，因此会调用eurekaTransport.queryClient.getApplications方法从服务端获取服务列表
    EurekaHttpResponse<Applications> httpResponse = clientConfig.getRegistryRefreshSingleVipAddress() == null
            ? eurekaTransport.queryClient.getApplications(remoteRegionsRef.get())
            : eurekaTransport.queryClient.getVip(clientConfig.getRegistryRefreshSingleVipAddress(), remoteRegionsRef.get());
    if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
        //返回对象就是服务列表
        apps = httpResponse.getEntity();
    }
    logger.info("The response status is {}", httpResponse.getStatusCode());

    if (apps == null) {...}
    else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
        //考虑到多线程同步，只有CAS成功的线程，才会把自己从Eureka server获取的数据来替换本地缓存
        localRegionApps.set(this.filterAndShuffle(apps));
    } else {...}
}

//EurekaHttpClientDecorator类#getApplications方法
@Override
public EurekaHttpResponse<Applications> getApplications(final String... regions) {
    //这里面涉及到配置是否重试
    return execute(new RequestExecutor<Applications>() {
        @Override
        public EurekaHttpResponse<Applications> execute(EurekaHttpClient delegate) {
            //调用AbstractJerseyEurekaHttpClient类
            return delegate.getApplications(regions);
        }

        @Override
        public RequestType getRequestType() {
            return RequestType.GetApplications;
        }
    });
}

@Override
public EurekaHttpResponse<Applications> getApplications(String... regions) {
    //取增量数据的path是"apps/delta"
    return getApplicationsInternal("apps/", regions);
}

//具体的请求响应处理都在此方法中
private EurekaHttpResponse<Applications> getApplicationsInternal(String urlPath, String[] regions) {
    ClientResponse response = null;
    String regionsParamValue = null;
    try {
        //jersey、resource这些关键词都预示着这是个restful请求
        WebResource webResource = jerseyClient.resource(serviceUrl).path(urlPath);
        if (regions != null && regions.length > 0) {
            regionsParamValue = StringUtil.join(regions);
            webResource = webResource.queryParam("regions", regionsParamValue);
        }
        Builder requestBuilder = webResource.getRequestBuilder();
        addExtraHeaders(requestBuilder);
        //发起网络请求，将响应封装成ClientResponse实例
        response = requestBuilder.accept(MediaType.APPLICATION_JSON_TYPE).get(ClientResponse.class);

        Applications applications = null;
        if (response.getStatus() == Status.OK.getStatusCode() && response.hasEntity()) {
            //取得全部应用信息
            applications = response.getEntity(Applications.class);
        }
        return anEurekaHttpResponse(response.getStatus(), Applications.class)
                .headers(headersOf(response))
                .entity(applications)
                .build();
    } finally {
        if (response != null) {
            response.close();
        }
    }
}

//总结：获取全量数据，是通过jersey-client库的API向Eureka server发起restful请求http://localhost:8761/eureka/apps实现的，并将响应的服务列表数据放在一个成员变量中作为本地缓存

【6.2.2】分析增量更新

//分析增量更新
//里面的一致性哈希码，本质上就是校验数据
//如：服务器上全量块存的是【ABCDEFG】,此时它的哈希码便是全量块存的数据的哈希值,增量块存的是【FG】，
//而我们客户端是【ABCD】，增量拉下来再合并，则为【ABCDFG】，得到的哈希值便会与全量哈希值不一致，代表了缺失一部分数据
//故检验不对就会全量拉取
private void getAndUpdateDelta(Applications applications) throws Throwable {
    long currentUpdateGeneration = fetchRegistryGeneration.get();

    Applications delta = null;
    //增量信息是通过eurekaTransport.queryClient.getDelta方法完成的
    EurekaHttpResponse<Applications> httpResponse = eurekaTransport.queryClient.getDelta(remoteRegionsRef.get());
    if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
        //delta中保存了Eureka server返回的增量更新
        delta = httpResponse.getEntity();
    }
    //如果没有
    if (delta == null) {
        //如果增量信息为空，就直接发起一次全量更新
        getAndStoreFullRegistry();
    }
    //考虑到多线程同步问题，这里通过CAS来确保请求发起到现在是线程安全的，
    //如果这期间fetchRegistryGeneration变了，就表示其他线程也做了类似操作，因此放弃本次响应的数据
    else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
        logger.debug("Got delta update with apps hashcode {}", delta.getAppsHashCode());
        String reconcileHashCode = "";
        if (fetchRegistryUpdateLock.tryLock()) {
            try {
                //用Eureka返回的增量数据和本地数据做合并操作
                updateDelta(delta);
                //用合并了增量数据之后的本地数据来生成一致性哈希码
                reconcileHashCode = getReconcileHashCode(applications);
            } finally {
                fetchRegistryUpdateLock.unlock();
            }
        } else {...}
        //Eureka server在返回增量更新数据时，也会返回服务端的一致性哈希码，
        //理论上每次本地缓存数据经历了多次增量更新后，计算出的一致性哈希码应该是和服务端一致的，
        //如果发现不一致，就证明本地缓存的服务列表信息和Eureka server不一致了，需要做一次全量更新
        if (!reconcileHashCode.equals(delta.getAppsHashCode()) || clientConfig.shouldLogDeltaDiff()) {
            //一致性哈希码不同，就在reconcileAndLogDifference方法中做全量更新
            reconcileAndLogDifference(delta, reconcileHashCode);  // this makes a remoteCall
        }
    } else {...}
}

//updateDelta方法将增量更新数据和本地数据做合并
private void updateDelta(Applications delta) {
    int deltaCount = 0;
    //遍历所有服务
    for (Application app : delta.getRegisteredApplications()) {
        //遍历当前服务的所有实例
        for (InstanceInfo instance : app.getInstances()) {
            //取出缓存的所有服务列表，用于合并
            Applications applications = getApplications();
            String instanceRegion = instanceRegionChecker.getInstanceRegion(instance);
            //判断正在处理的实例和当前应用是否在同一个region
            if (!instanceRegionChecker.isLocalRegion(instanceRegion)) {
                //如果不是同一个region，接下来合并的数据就换成专门为其他region准备的缓存
                Applications remoteApps = remoteRegionVsApps.get(instanceRegion);
                if (null == remoteApps) {
                    remoteApps = new Applications();
                    remoteRegionVsApps.put(instanceRegion, remoteApps);
                }
                applications = remoteApps;
            }

            ++deltaCount;
             //对新增的实例的处理
            if (ActionType.ADDED.equals(instance.getActionType())) {
                Application existingApp = applications.getRegisteredApplications(instance.getAppName());
                if (existingApp == null) {
                    applications.addApplication(app);
                }
                logger.debug("Added instance {} to the existing apps in region {}", instance.getId(), instanceRegion);
                applications.getRegisteredApplications(instance.getAppName()).addInstance(instance);
            }
             //对修改实例的处理
            else if (ActionType.MODIFIED.equals(instance.getActionType())) {
                Application existingApp = applications.getRegisteredApplications(instance.getAppName());
                if (existingApp == null) {
                    applications.addApplication(app);
                }
                logger.debug("Modified instance {} to the existing apps ", instance.getId());

                applications.getRegisteredApplications(instance.getAppName()).addInstance(instance);

            }
            //对删除实例的处理
            else if (ActionType.DELETED.equals(instance.getActionType())) {
                Application existingApp = applications.getRegisteredApplications(instance.getAppName());
                if (existingApp != null) {
                    logger.debug("Deleted instance {} to the existing apps ", instance.getId());
                    existingApp.removeInstance(instance);
                    /*
                     * We find all instance list from application(The status of instance status is not only the status is UP but also other status)
                     * if instance list is empty, we remove the application.
                     */
                    if (existingApp.getInstancesAsIsFromEureka().isEmpty()) {
                        applications.removeApplication(existingApp);
                    }
                }
            }
        }
    }
    logger.debug("The total number of instances fetched by the delta processor : {}", deltaCount);

    getApplications().setVersion(delta.getVersion());
    //整理数据，使得后续使用过程中，这些应用的实例总是以相同顺序返回
    getApplications().shuffleInstances(clientConfig.shouldFilterOnlyUpInstances());
    //和当前应用不在同一个region的应用，其实例数据也要整理
    for (Applications applications : remoteRegionVsApps.values()) {
        applications.setVersion(delta.getVersion());
        applications.shuffleInstances(clientConfig.shouldFilterOnlyUpInstances());
    }
}

【6.3】分析服务定时续约任务 HeartbeatThread（也就是心跳机制）

private class HeartbeatThread implements Runnable {

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

boolean renew() {
    EurekaHttpResponse<InstanceInfo> httpResponse;
    try {
        //发送心跳请求
        httpResponse = eurekaTransport.registrationClient.sendHeartBeat(instanceInfo.getAppName(), instanceInfo.getId(), instanceInfo, null);
        logger.debug(PREFIX + "{} - Heartbeat status: {}", appPathIdentifier, httpResponse.getStatusCode());
        if (httpResponse.getStatusCode() == Status.NOT_FOUND.getStatusCode()) {
            REREGISTER_COUNTER.increment();
            logger.info(PREFIX + "{} - Re-registering apps/{}", appPathIdentifier, instanceInfo.getAppName());
            long timestamp = instanceInfo.setIsDirtyWithTime();
            boolean success = register();
            if (success) {
                instanceInfo.unsetIsDirty(timestamp);
            }
            return success;
        }
        return httpResponse.getStatusCode() == Status.OK.getStatusCode();
    } catch (Throwable e) {
        logger.error(PREFIX + "{} - was unable to send heartbeat!", appPathIdentifier, e);
        return false;
    }
}

【7】分析服务注册的instanceInfoReplicator.start方法

public void start(int initialDelayMs) {
    if (started.compareAndSet(false, true)) {
        instanceInfo.setIsDirty();  // for initial register
        Future next = scheduler.schedule(this, initialDelayMs, TimeUnit.SECONDS);
        scheduledPeriodicRef.set(next);
    }
}

//InstanceInfoReplicator类#run方法
public void run() {
    try {
        discoveryClient.refreshInstanceInfo();

        Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
        if (dirtyTimestamp != null) {
            //服务注册
            discoveryClient.register();
            instanceInfo.unsetIsDirty(dirtyTimestamp);
        }
    } catch (Throwable t) {
        logger.warn("There was a problem with the instance info replicator", t);
    } finally {
        Future next = scheduler.schedule(this, replicationIntervalSeconds, TimeUnit.SECONDS);
        scheduledPeriodicRef.set(next);
    }
}

boolean register() throws Throwable {
    logger.info(PREFIX + "{}: registering service...", appPathIdentifier);
    EurekaHttpResponse<Void> httpResponse;
    try {
        //发起注册请求
        httpResponse = eurekaTransport.registrationClient.register(instanceInfo);
    } catch (Exception e) {
        logger.warn(PREFIX + "{} - registration failed {}", appPathIdentifier, e.getMessage(), e);
        throw e;
    }
    return httpResponse.getStatusCode() == Status.NO_CONTENT.getStatusCode();
}

【8】Eureka Server服务端Jersey接口部分分析

【8.1】服务端Jersey接口处理类ApplicationResource

@Produces({"application/xml", "application/json"})
public class ApplicationResource {
    ...
    //注册一个实例的信息
    @POST
    @Consumes({"application/json", "application/xml"})
    public Response addInstance(InstanceInfo info,
                                @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
        logger.debug("Registering instance {} (replication={})", info.getId(), isReplication);
        // validate that the instanceinfo contains all the necessary required fields
        // 参数校验，不符合验证规则的，返回400状态码，
        if (isBlank(info.getId())) {
            return Response.status(400).entity("Missing instanceId").build();
        } else if (isBlank(info.getHostName())) {
            return Response.status(400).entity("Missing hostname").build();
        } else if (isBlank(info.getIPAddr())) {
            return Response.status(400).entity("Missing ip address").build();
        } else if (isBlank(info.getAppName())) {
            return Response.status(400).entity("Missing appName").build();
        } else if (!appName.equals(info.getAppName())) {
            return Response.status(400).entity("Mismatched appName, expecting " + appName + " but was " + info.getAppName()).build();
        } else if (info.getDataCenterInfo() == null) {
            return Response.status(400).entity("Missing dataCenterInfo").build();
        } else if (info.getDataCenterInfo().getName() == null) {
            return Response.status(400).entity("Missing dataCenterInfo Name").build();
        }

        // handle cases where clients may be registering with bad DataCenterInfo with missing data
        DataCenterInfo dataCenterInfo = info.getDataCenterInfo();
        if (dataCenterInfo instanceof UniqueIdentifier) {
            String dataCenterInfoId = ((UniqueIdentifier) dataCenterInfo).getId();
            if (isBlank(dataCenterInfoId)) {
                boolean experimental = "true".equalsIgnoreCase(serverConfig.getExperimental("registration.validation.dataCenterInfoId"));
                if (experimental) {
                    String entity = "DataCenterInfo of type " + dataCenterInfo.getClass() + " must contain a valid id";
                    return Response.status(400).entity(entity).build();
                } else if (dataCenterInfo instanceof AmazonInfo) {
                    AmazonInfo amazonInfo = (AmazonInfo) dataCenterInfo;
                    String effectiveId = amazonInfo.get(AmazonInfo.MetaDataKey.instanceId);
                    if (effectiveId == null) {
                        amazonInfo.getMetadata().put(AmazonInfo.MetaDataKey.instanceId.getName(), info.getId());
                    }
                } else {
                    logger.warn("Registering DataCenterInfo of type {} without an appropriate id", dataCenterInfo.getClass());
                }
            }
        }
        // 重点在这里，进行注册
        registry.register(info, "true".equals(isReplication));
        return Response.status(204).build();  // 204 to be backwards compatible
    }

}

【8.1.1】注册方法分析

@Override
public void register(final InstanceInfo info, final boolean isReplication) {
    int leaseDuration = Lease.DEFAULT_DURATION_IN_SECS;
    if (info.getLeaseInfo() != null && info.getLeaseInfo().getDurationInSecs() > 0) {
        leaseDuration = info.getLeaseInfo().getDurationInSecs();
    }
    super.register(info, leaseDuration, isReplication);
    replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication);
}

//AbstractInstanceRegistry类#register方法
public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {
    try {
        // 上只读锁
        read.lock();
        // 从本地MAP里面获取当前实例的信息
        //注册表的结构
        Map<String, Lease<InstanceInfo>> gMap = registry.get(registrant.getAppName());
        // 增加注册次数到监控信息里面去。
        REGISTER.increment(isReplication);
        if (gMap == null) {
            // 如果第一次进来，那么gMap为空，则创建一个ConcurrentHashMap放入到registry里面去
            final ConcurrentHashMap<String, Lease<InstanceInfo>> gNewMap = new ConcurrentHashMap<String, Lease<InstanceInfo>>();
            // putIfAbsent方法主要是在向ConcurrentHashMap中添加键—值对的时候，它会先判断该键值对是否已经存在。
            // 如果不存在（新的entry），那么会向map中添加该键值对，并返回null。
            // 如果已经存在，那么不会覆盖已有的值，直接返回已经存在的值。
            gMap = registry.putIfAbsent(registrant.getAppName(), gNewMap);
            if (gMap == null) {
                // 表明map中确实不存在，则设置gMap为最新创建的那个
                gMap = gNewMap;
            }
        }
        // 从MAP中查询已经存在的Lease信息 （比如第二次来）
        Lease<InstanceInfo> existingLease = gMap.get(registrant.getId());
        // 当Lease的对象不为空时。
        if (existingLease != null && (existingLease.getHolder() != null)) {
            // 当instance已经存在是，和客户端的instance的信息做比较，时间最新的那个，为有效instance信息
            Long existingLastDirtyTimestamp = existingLease.getHolder().getLastDirtyTimestamp();
            Long registrationLastDirtyTimestamp = registrant.getLastDirtyTimestamp();

            if (existingLastDirtyTimestamp > registrationLastDirtyTimestamp) {
                registrant = existingLease.getHolder();
            }
        } else {
            // 这里只有当existinglease不存在时，才会进来。 像那种恢复心跳，信息过期的，都不会进入这里。
            // Eureka‐Server的自我保护机制做的操作，为每分钟最大续约数+2 ，同时重新计算每分钟最小续约数
            synchronized (lock) {
                if (this.expectedNumberOfClientsSendingRenews > 0) {
                    // Since the client wants to register it, increase the number of clients sending renews
                    this.expectedNumberOfClientsSendingRenews = this.expectedNumberOfClientsSendingRenews + 1;
                    updateRenewsPerMinThreshold();
                }
            }
        }
        // 构建一个最新的Lease信息
        Lease<InstanceInfo> lease = new Lease<InstanceInfo>(registrant, leaseDuration);
        if (existingLease != null) {
            // 当原来存在Lease的信息时，设置他的serviceUpTimestamp, 保证服务开启的时间一直是第一次的那个
            lease.setServiceUpTimestamp(existingLease.getServiceUpTimestamp());
        }
        // 放入本地Map中
        gMap.put(registrant.getId(), lease);
        // 添加到最近的注册队列里面去，以时间戳作为Key， 名称作为value，主要是为了运维界面的统计数据。
        synchronized (recentRegisteredQueue) {
            recentRegisteredQueue.add(new Pair<Long, String>(
                    System.currentTimeMillis(),
                    registrant.getAppName() + "(" + registrant.getId() + ")"));
        }
        // 分析instanceStatus
        if (!InstanceStatus.UNKNOWN.equals(registrant.getOverriddenStatus())) {
            logger.debug("Found overridden status {} for instance {}. Checking to see if needs to be add to the "
                            + "overrides", registrant.getOverriddenStatus(), registrant.getId());
            if (!overriddenInstanceStatusMap.containsKey(registrant.getId())) {
                logger.info("Not found overridden id {} and hence adding it", registrant.getId());
                overriddenInstanceStatusMap.put(registrant.getId(), registrant.getOverriddenStatus());
            }
        }
        InstanceStatus overriddenStatusFromMap = overriddenInstanceStatusMap.get(registrant.getId());
        if (overriddenStatusFromMap != null) {
            logger.info("Storing overridden status {} from map", overriddenStatusFromMap);
            registrant.setOverriddenStatus(overriddenStatusFromMap);
        }

        // Set the status based on the overridden status rules
        InstanceStatus overriddenInstanceStatus = getOverriddenInstanceStatus(registrant, existingLease, isReplication);
        registrant.setStatusWithoutDirty(overriddenInstanceStatus);

        // 得到instanceStatus，判断是否是UP状态，
        if (InstanceStatus.UP.equals(registrant.getStatus())) {
            lease.serviceUp();
        }
        // 设置注册类型为添加
        registrant.setActionType(ActionType.ADDED);
        // 租约变更记录队列，记录了实例的每次变化， 用于注册信息的增量获取、
        recentlyChangedQueue.add(new RecentlyChangedItem(lease));
        registrant.setLastUpdatedTimestamp();
         // 清理缓存 ，传入的参数为key
        invalidateCache(registrant.getAppName(), registrant.getVIPAddress(), registrant.getSecureVipAddress());
    } finally {
        read.unlock();
    }
}

【8.1.1】分析Lease结构

public class Lease<T> {

    enum Action {
        Register, Cancel, Renew
    };
    //租约过期的时间常量，默认90秒，也就说90秒没有心跳过来，那么这边将会自动剔除该节点
    public static final int DEFAULT_DURATION_IN_SECS = 90;
    这个租约是属于谁的， 目前占用这个属性的是
    private T holder;
    //租约是啥时候过期的，当服务下线的时候，会过来更新这个时间戳registrationTimestamp ： 租约的注册时间
    private long evictionTimestamp;
    private long registrationTimestamp;
    //服务启动时间 ，当客户端在注册的时候，instanceInfo的status 为UP的时候，则更新这个时间戳
    private long serviceUpTimestamp;
    //最后更新时间，每次续约的时候，都会更新这个时间戳，在判断实例是否过期时，需要用到这个属性。
    private volatile long lastUpdateTimestamp;
    //过期时间，毫秒单位
    private long duration;

    public Lease(T r, int durationInSecs) {
        holder = r;
        registrationTimestamp = System.currentTimeMillis();
        lastUpdateTimestamp = registrationTimestamp;
        duration = (durationInSecs * 1000);

    }

    //更新的时候设置过期时间为当前时间+90S
    public void renew() {
        lastUpdateTimestamp = System.currentTimeMillis() + duration;

    }

    public void cancel() {
        if (evictionTimestamp <= 0) {
            evictionTimestamp = System.currentTimeMillis();
        }
    }

    public void serviceUp() {
        if (serviceUpTimestamp == 0) {
            serviceUpTimestamp = System.currentTimeMillis();
        }
    }

    public void setServiceUpTimestamp(long serviceUpTimestamp) {
        this.serviceUpTimestamp = serviceUpTimestamp;
    }

    public boolean isExpired() {
        return isExpired(0l);
    }
    //这里面存在的问题是过期时间+90S
    //实际上也就是在更新时候的180s之后才算过期
    public boolean isExpired(long additionalLeaseMs) {
        return (evictionTimestamp > 0 || System.currentTimeMillis() > (lastUpdateTimestamp + duration + additionalLeaseMs));
    }

    public long getRegistrationTimestamp() {
        return registrationTimestamp;
    }

    public long getLastRenewalTimestamp() {
        return lastUpdateTimestamp;
    }

    public long getEvictionTimestamp() {
        return evictionTimestamp;
    }

    public long getServiceUpTimestamp() {
        return serviceUpTimestamp;
    }

    public T getHolder() {
        return holder;
    }

}

【8.2】客户端Jersey接口处理类ApplicationsResource

@Path("/{version}/apps")
@Produces({"application/xml", "application/json"})
public class ApplicationsResource {
    ...
    private final EurekaServerConfig serverConfig;
    private final PeerAwareInstanceRegistry registry;
    private final ResponseCache responseCache;

    @Inject
    ApplicationsResource(EurekaServerContext eurekaServer) {
        this.serverConfig = eurekaServer.getServerConfig();
        this.registry = eurekaServer.getRegistry();
        this.responseCache = registry.getResponseCache();
    }

    public ApplicationsResource() {
        this(EurekaServerContextHolder.getInstance().getServerContext());
    }

    //获取关于特定{@link com.netflix.discovery.shared.Application}的信息。
    @Path("{appId}")
    public ApplicationResource getApplicationResource(
            @PathParam("version") String version,
            @PathParam("appId") String appId) {
        CurrentRequestVersion.set(Version.toEnum(version));
        return new ApplicationResource(appId, serverConfig, registry);
    }

    //获取关于所有{@link com.netflix.discovery.shared.Applications}的信息。
    @GET
    public Response getContainers(@PathParam("version") String version,
                                  @HeaderParam(HEADER_ACCEPT) String acceptHeader,
                                  @HeaderParam(HEADER_ACCEPT_ENCODING) String acceptEncoding,
                                  @HeaderParam(EurekaAccept.HTTP_X_EUREKA_ACCEPT) String eurekaAccept,
                                  @Context UriInfo uriInfo,
                                  @Nullable @QueryParam("regions") String regionsStr) {

        boolean isRemoteRegionRequested = null != regionsStr && !regionsStr.isEmpty();
        String[] regions = null;
        if (!isRemoteRegionRequested) {
            EurekaMonitors.GET_ALL.increment();
        } else {
            regions = regionsStr.toLowerCase().split(",");
            Arrays.sort(regions); // So we don't have different caches for same regions queried in different order.
            EurekaMonitors.GET_ALL_WITH_REMOTE_REGIONS.increment();
        }

        // Check if the server allows the access to the registry. The server can
        // restrict access if it is not
        // ready to serve traffic depending on various reasons.
        if (!registry.shouldAllowAccess(isRemoteRegionRequested)) {
            return Response.status(Status.FORBIDDEN).build();
        }
        CurrentRequestVersion.set(Version.toEnum(version));
        KeyType keyType = Key.KeyType.JSON;
        String returnMediaType = MediaType.APPLICATION_JSON;
        if (acceptHeader == null || !acceptHeader.contains(HEADER_JSON_VALUE)) {
            keyType = Key.KeyType.XML;
            returnMediaType = MediaType.APPLICATION_XML;
        }
        //获取服务实例对应的缓存key
        Key cacheKey = new Key(Key.EntityType.Application,
                ResponseCacheImpl.ALL_APPS,
                keyType, CurrentRequestVersion.get(), EurekaAccept.fromString(eurekaAccept), regions
        );

        Response response;
        //是否压缩
        if (acceptEncoding != null && acceptEncoding.contains(HEADER_GZIP_VALUE)) {
            response = Response.ok(responseCache.getGZIP(cacheKey))
                    .header(HEADER_CONTENT_ENCODING, HEADER_GZIP_VALUE)
                    .header(HEADER_CONTENT_TYPE, returnMediaType)
                    .build();
        } else {
            //从缓存里获取服务实例注册信息
            response = Response.ok(responseCache.get(cacheKey))
                    .build();
        }
        return response;
    }

    //在{@link com.netflix.discovery.shared.Applications}中获取关于所有增量更改的信息。
    @Path("delta")
    @GET
    public Response getContainerDifferential(
            @PathParam("version") String version,
            @HeaderParam(HEADER_ACCEPT) String acceptHeader,
            @HeaderParam(HEADER_ACCEPT_ENCODING) String acceptEncoding,
            @HeaderParam(EurekaAccept.HTTP_X_EUREKA_ACCEPT) String eurekaAccept,
            @Context UriInfo uriInfo, @Nullable @QueryParam("regions") String regionsStr) {

        boolean isRemoteRegionRequested = null != regionsStr && !regionsStr.isEmpty();

        // If the delta flag is disabled in discovery or if the lease expiration
        // has been disabled, redirect clients to get all instances
        if ((serverConfig.shouldDisableDelta()) || (!registry.shouldAllowAccess(isRemoteRegionRequested))) {
            return Response.status(Status.FORBIDDEN).build();
        }

        String[] regions = null;
        if (!isRemoteRegionRequested) {
            EurekaMonitors.GET_ALL_DELTA.increment();
        } else {
            regions = regionsStr.toLowerCase().split(",");
            Arrays.sort(regions); // So we don't have different caches for same regions queried in different order.
            EurekaMonitors.GET_ALL_DELTA_WITH_REMOTE_REGIONS.increment();
        }

        CurrentRequestVersion.set(Version.toEnum(version));
        KeyType keyType = Key.KeyType.JSON;
        String returnMediaType = MediaType.APPLICATION_JSON;
        if (acceptHeader == null || !acceptHeader.contains(HEADER_JSON_VALUE)) {
            keyType = Key.KeyType.XML;
            returnMediaType = MediaType.APPLICATION_XML;
        }

        Key cacheKey = new Key(Key.EntityType.Application,
                ResponseCacheImpl.ALL_APPS_DELTA,
                keyType, CurrentRequestVersion.get(), EurekaAccept.fromString(eurekaAccept), regions
        );

        if (acceptEncoding != null
                && acceptEncoding.contains(HEADER_GZIP_VALUE)) {
            return Response.ok(responseCache.getGZIP(cacheKey))
                    .header(HEADER_CONTENT_ENCODING, HEADER_GZIP_VALUE)
                    .header(HEADER_CONTENT_TYPE, returnMediaType)
                    .build();
        } else {
            return Response.ok(responseCache.get(cacheKey))
                    .build();
        }
    }
}

【8.2.1】ApplicationsResource类的getContainers方法分析

//获取关于所有{@link com.netflix.discovery.shared.Applications}的信息。
@GET
public Response getContainers(@PathParam("version") String version, @HeaderParam(HEADER_ACCEPT) String acceptHeader,
                              @HeaderParam(HEADER_ACCEPT_ENCODING) String acceptEncoding, @HeaderParam(EurekaAccept.HTTP_X_EUREKA_ACCEPT) String eurekaAccept,
                              @Context UriInfo uriInfo, @Nullable @QueryParam("regions") String regionsStr) {

    boolean isRemoteRegionRequested = null != regionsStr && !regionsStr.isEmpty();
    String[] regions = null;
    if (!isRemoteRegionRequested) {
        EurekaMonitors.GET_ALL.increment();
    } else {
        regions = regionsStr.toLowerCase().split(",");
        Arrays.sort(regions); // So we don't have different caches for same regions queried in different order.
        EurekaMonitors.GET_ALL_WITH_REMOTE_REGIONS.increment();
    }

    // Check if the server allows the access to the registry. The server can
    // restrict access if it is not
    // ready to serve traffic depending on various reasons.
    if (!registry.shouldAllowAccess(isRemoteRegionRequested)) {
        return Response.status(Status.FORBIDDEN).build();
    }
    CurrentRequestVersion.set(Version.toEnum(version));
    KeyType keyType = Key.KeyType.JSON;
    String returnMediaType = MediaType.APPLICATION_JSON;
    if (acceptHeader == null || !acceptHeader.contains(HEADER_JSON_VALUE)) {
        keyType = Key.KeyType.XML;
        returnMediaType = MediaType.APPLICATION_XML;
    }
    //获取服务实例对应的缓存key
    Key cacheKey = new Key(Key.EntityType.Application,
            ResponseCacheImpl.ALL_APPS,
            keyType, CurrentRequestVersion.get(), EurekaAccept.fromString(eurekaAccept), regions
    );

    Response response;
    //是否压缩
    if (acceptEncoding != null && acceptEncoding.contains(HEADER_GZIP_VALUE)) {
        response = Response.ok(responseCache.getGZIP(cacheKey))
                .header(HEADER_CONTENT_ENCODING, HEADER_GZIP_VALUE)
                .header(HEADER_CONTENT_TYPE, returnMediaType)
                .build();
    } else {
        //从缓存里获取服务实例注册信息，从ResponseCacheImpl类中获取
        response = Response.ok(responseCache.get(cacheKey))
                .build();
    }
    return response;
}

//分析responseCache.get方法
//ResponseCacheImpl类#get方法
public String get(final Key key) {
    return get(key, shouldUseReadOnlyResponseCache);
}

@VisibleForTesting
String get(final Key key, boolean useReadOnlyCache) {
    Value payload = getValue(key, useReadOnlyCache);
    if (payload == null || payload.getPayload().equals(EMPTY_PAYLOAD)) {
        return null;
    } else {
        return payload.getPayload();
    }
}

//精髓设计的点，利用了读写分离，有种CopyOnWrite的思维
//private final ConcurrentMap<Key, Value> readOnlyCacheMap = new ConcurrentHashMap<Key, Value>();
//private final LoadingCache<Key, Value> readWriteCacheMap;
@VisibleForTesting
Value getValue(final Key key, boolean useReadOnlyCache) {
    Value payload = null;
    try {
        //只读缓存的开启
        if (useReadOnlyCache) {
            final Value currentPayload = readOnlyCacheMap.get(key);
            //只读缓存拿不到才去读写缓存里面拿
            if (currentPayload != null) {
                payload = currentPayload;
            } else {
                payload = readWriteCacheMap.get(key);
                readOnlyCacheMap.put(key, payload);
            }
        } else {
            payload = readWriteCacheMap.get(key);
        }
    } catch (Throwable t) {...}
    return payload;
}

//ResponseCacheImpl类#构造方法
ResponseCacheImpl(EurekaServerConfig serverConfig, ServerCodecs serverCodecs, AbstractInstanceRegistry registry) {
    this.serverConfig = serverConfig;
    this.serverCodecs = serverCodecs;
    this.shouldUseReadOnlyResponseCache = serverConfig.shouldUseReadOnlyResponseCache();
    this.registry = registry;

    long responseCacheUpdateIntervalMs = serverConfig.getResponseCacheUpdateIntervalMs();
    this.readWriteCacheMap =
            CacheBuilder.newBuilder().initialCapacity(serverConfig.getInitialCapacityOfResponseCache())
                    //读写缓存默认180秒会自动定时过期
                    .expireAfterWrite(serverConfig.getResponseCacheAutoExpirationInSeconds(), TimeUnit.SECONDS)
                    .removalListener(new RemovalListener<Key, Value>() {
                        @Override
                        public void onRemoval(RemovalNotification<Key, Value> notification) {
                            Key removedKey = notification.getKey();
                            if (removedKey.hasRegions()) {
                                Key cloneWithNoRegions = removedKey.cloneWithoutRegions();
                                regionSpecificKeys.remove(cloneWithNoRegions, removedKey);
                            }
                        }
                    })
                    .build(new CacheLoader<Key, Value>() {
                        @Override
                        public Value load(Key key) throws Exception {
                            if (key.hasRegions()) {
                                Key cloneWithNoRegions = key.cloneWithoutRegions();
                                regionSpecificKeys.put(cloneWithNoRegions, key);
                            }
                            //从内存注册表中获取
                            Value value = generatePayload(key);
                            return value;
                        }
                    });

    if (shouldUseReadOnlyResponseCache) {
        //默认30秒用读写缓存的数据更新只读缓存的数据
        timer.schedule(getCacheUpdateTask(),
                new Date(((System.currentTimeMillis() / responseCacheUpdateIntervalMs) * responseCacheUpdateIntervalMs)
                        + responseCacheUpdateIntervalMs),
                responseCacheUpdateIntervalMs);
    }

    try {
        Monitors.registerObject(this);
    } catch (Throwable e) {...}
}

Eureka服务端源码分析图

Eureka服务端Jersey接口分析图

　　　　

Eureka客户端源码分析图