目录
- Eureka Client启动并调用Eureka Server的注册接口
Eureka Client启动并调用Eureka Server的注册接口
Spring Cloud Eureka的自动配置
@EnableDiscoveryClient
首先从使用Eureka Client必须引入的@EnableDiscoveryClient注解说起
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(EnableDiscoveryClientImportSelector.class)
public @interface EnableDiscoveryClient {
/**
* If true, the ServiceRegistry will automatically register the local server.
*/
boolean autoRegister() default true;
}@EnableDiscoveryClient注解的作用：
autoRegister默认值为true，即服务发现客户端默认会自动注册到服务端
Import导入
EnableDiscoveryClientImportSelector.class，其作用是导入了 spring-cloud-eureka-client.jar!\META-INF\spring.factories 中的
EurekaDiscoveryClientConfigurationorg.springframework.cloud.client.discovery.EnableDiscoveryClient=\ org.springframework.cloud.netflix.eureka.EurekaDiscoveryClientConfiguration由于autoRegister默认为true，故还会导入
AutoServiceRegistrationConfiguration，即启用自动服务注册的配置，等同于在配置文件中spring.cloud.service-registry.auto-registration.enabled = true
EurekaDiscoveryClientConfiguration
- 向Spring容器注册EurekaDiscoveryClientConfiguration.Marker.class，使得真正导入DiscoveryClient的
EurekaClientAutoConfiguration配置类满足启用条件 - 创建监听
RefreshScopeRefreshedEvent事件的监听器，满足在使用RefreshScope刷新时可以重建EurekaClient（不是本文重点） - 在配置
eureka.client.healthcheck.enabled=true的前提下，向Spring容器注册EurekaHealthCheckHandler用于健康检查（不是本文重点）
所以，EurekaDiscoveryClientConfiguration的主要作用是向Spring容器注册EurekaDiscoveryClientConfiguration.Marker.class，使得EurekaClientAutoConfiguration配置类满足启用条件
EurekaClientAutoConfiguration
EurekaClientAutoConfiguration配置类中涉及的内容比较多，主要内容：
- 1、注册了spring cloud包下的
EurekaClientConfigBean，这是个对netflix的EurekaClientConfig客户端配置接口的实现 - 2、注册了spring cloud包下的
EurekaInstanceConfigBean，这是个对netflix的EurekaInstanceConfig实例信息配置接口的实现 - 3、注册了一些AutoServiceRegistration，即客户端自动注册的组件，如
EurekaRegistration： Eureka实例的服务注册信息（在开启客户端自动注册时才会注册）EurekaServiceRegistry： Eureka服务注册器EurekaAutoServiceRegistration： Eureka服务自动注册器，实现了SmartLifecycle，会在Spring容器的refresh的最后阶段被调用，通过EurekaServiceRegistry注册器注册EurekaRegistration信息
- 4、注册netflix的
EurekaClient和ApplicationInfoManager，注册时分为两种情况，即是否满足RefreshScope，如果满足，注入的Bean是带有 @Lazy + @RefreshScope 注解的ApplicationInfoManager： 管理并初始化当前Instance实例的注册信息，并提供了实例状态监听机制EurekaClient： netflix的接口类，用于和Eureka Server交互的客户端，而netflix的默认实现是DiscoveryClient，也是本文分析的重点
- 5、注册
EurekaHealthIndicator，为/health端点提供Eureka相关信息，主要有Status当前实例状态和applications服务列表，在从Eureka Server获取服务列表正常的情况下，Status使用Eureka Server上的InstanceRemoteStatus，不正常情况下，代码中有一些判断逻辑
public class EurekaClientAutoConfiguration {
...省略
/**
* 1、注册EurekaClientConfigBean
*/
@Bean
@ConditionalOnMissingBean(value = EurekaClientConfig.class, search = SearchStrategy.CURRENT)
public EurekaClientConfigBean eurekaClientConfigBean() {
EurekaClientConfigBean client = new EurekaClientConfigBean();
if ("bootstrap".equals(propertyResolver.getProperty("spring.config.name"))) {
// We don't register during bootstrap by default, but there will be another
// chance later.
client.setRegisterWithEureka(false);
}
return client;
}
/**
* 2、注册EurekaInstanceConfigBean
*/
@Bean
@ConditionalOnMissingBean(value = EurekaInstanceConfig.class, search = SearchStrategy.CURRENT)
public EurekaInstanceConfigBean eurekaInstanceConfigBean(InetUtils inetUtils) throws MalformedURLException {
PropertyResolver eurekaPropertyResolver = new RelaxedPropertyResolver(this.env, "eureka.instance.");
String hostname = eurekaPropertyResolver.getProperty("hostname");
boolean preferIpAddress = Boolean.parseBoolean(eurekaPropertyResolver.getProperty("preferIpAddress"));
int nonSecurePort = Integer.valueOf(propertyResolver.getProperty("server.port", propertyResolver.getProperty("port", "8080")));
int managementPort = Integer.valueOf(propertyResolver.getProperty("management.port", String.valueOf(nonSecurePort)));
String managementContextPath = propertyResolver.getProperty("management.contextPath", propertyResolver.getProperty("server.contextPath", "/"));
EurekaInstanceConfigBean instance = new EurekaInstanceConfigBean(inetUtils);
instance.setNonSecurePort(nonSecurePort);
instance.setInstanceId(getDefaultInstanceId(propertyResolver));
instance.setPreferIpAddress(preferIpAddress);
if (managementPort != nonSecurePort && managementPort != 0) {
if (StringUtils.hasText(hostname)) {
instance.setHostname(hostname);
}
String statusPageUrlPath = eurekaPropertyResolver.getProperty("statusPageUrlPath");
String healthCheckUrlPath = eurekaPropertyResolver.getProperty("healthCheckUrlPath");
if (!managementContextPath.endsWith("/")) {
managementContextPath = managementContextPath + "/";
}
if (StringUtils.hasText(statusPageUrlPath)) {
instance.setStatusPageUrlPath(statusPageUrlPath);
}
if (StringUtils.hasText(healthCheckUrlPath)) {
instance.setHealthCheckUrlPath(healthCheckUrlPath);
}
String scheme = instance.getSecurePortEnabled() ? "https" : "http";
URL base = new URL(scheme, instance.getHostname(), managementPort, managementContextPath);
instance.setStatusPageUrl(new URL(base, StringUtils.trimLeadingCharacter(instance.getStatusPageUrlPath(), '/')).toString());
instance.setHealthCheckUrl(new URL(base, StringUtils.trimLeadingCharacter(instance.getHealthCheckUrlPath(), '/')).toString());
}
return instance;
}
/**
* 3、注册客户端自动注册相关组件
* EurekaRegistration： Eureka实例的服务注册信息（在开启客户端自动注册时才会注册）
* EurekaServiceRegistry： Eureka服务注册器
* EurekaAutoServiceRegistration： Eureka服务自动注册器，
* 通过EurekaServiceRegistry注册器注册EurekaRegistration信息
*/
@Bean
public EurekaServiceRegistry eurekaServiceRegistry() {
return new EurekaServiceRegistry();
}
@Bean
@ConditionalOnBean(AutoServiceRegistrationProperties.class)
@ConditionalOnProperty(value = "spring.cloud.service-registry.auto-registration.enabled", matchIfMissing = true)
public EurekaRegistration eurekaRegistration(EurekaClient eurekaClient, CloudEurekaInstanceConfig instanceConfig, ApplicationInfoManager applicationInfoManager) {
return EurekaRegistration.builder(instanceConfig)
.with(applicationInfoManager)
.with(eurekaClient)
.with(healthCheckHandler)
.build();
}
@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);
}
/**
* 4、注册netflix的 EurekaClient 和 ApplicationInfoManager
*/
// 如果禁用客户端自动注册，在此方法debug打断点会触发服务注册，状态为STARTING
@Bean
public DiscoveryClient discoveryClient(EurekaInstanceConfig config, EurekaClient client) {
return new EurekaDiscoveryClient(config, client);
}
// 普通的EurekaClient配置（不可刷新）
@Configuration
@ConditionalOnMissingRefreshScope
protected static class EurekaClientConfiguration {
@Autowired
private ApplicationContext context;
@Autowired(required = false)
private DiscoveryClientOptionalArgs 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);
}
}
// 可刷新的EurekaClient配置类
@Configuration
@ConditionalOnRefreshScope //满足@ConditionalOnClass(RefreshScope.class)
// @ConditionalOnBean(RefreshAutoConfiguration.class)
protected static class RefreshableEurekaClientConfiguration {
@Autowired
private ApplicationContext context;
@Autowired(required = false)
private DiscoveryClientOptionalArgs optionalArgs;
// 注册CloudEurekaClient，是com.netflix.discovery.EurekaClient接口的实现类
@Bean(destroyMethod = "shutdown")
@ConditionalOnMissingBean(value = EurekaClient.class, search = SearchStrategy.CURRENT)
@org.springframework.cloud.context.config.annotation.RefreshScope
@Lazy
public EurekaClient eurekaClient(ApplicationInfoManager manager, EurekaClientConfig config, EurekaInstanceConfig instance) {
manager.getInfo(); // force initialization
return new CloudEurekaClient(manager, config, this.optionalArgs,
this.context);
}
// 注册ApplicationInfoManager
@Bean
@ConditionalOnMissingBean(value = ApplicationInfoManager.class, search = SearchStrategy.CURRENT)
@org.springframework.cloud.context.config.annotation.RefreshScope
@Lazy
public ApplicationInfoManager eurekaApplicationInfoManager(EurekaInstanceConfig config) {
InstanceInfo instanceInfo = new InstanceInfoFactory().create(config);
return new ApplicationInfoManager(config, instanceInfo);
}
}
/**
* 5、注册 EurekaHealthIndicator
*/
@Configuration
@ConditionalOnClass(Endpoint.class)
protected static class EurekaHealthIndicatorConfiguration {
@Bean
@ConditionalOnMissingBean
public EurekaHealthIndicator eurekaHealthIndicator(EurekaClient eurekaClient,
EurekaInstanceConfig instanceConfig, EurekaClientConfig clientConfig) {
return new EurekaHealthIndicator(eurekaClient, instanceConfig, clientConfig);
}
}
}如上，在满足一系列Conditional条件后，会向Spring容器中注册CloudEurekaClient，它是com.netflix.discovery.EurekaClient接口的实现类，具体继承实现关系如下
DiscoveryClient继承实现关系
如上图所示，刚刚创建的CloudEurekaClient是 com.netflix.discovery.DiscoveryClient的子类，它们都实现了com.netflix.discovery.EurekaClient接口
EurekaClient是Netflix对服务发现客户端抽象的接口，包含很多方法，而DiscoveryClient是其默认实现，也是本文分析的重点，CloudEurekaClient是spring cloud的实现，根据类上注释，其主要重写了onCacheRefreshed()方法，这个方法主要是从Eureka Server fetchRegistry()获取服务列表之后用于以广播方式通知缓存刷新事件的，其实DiscoveryClient也有onCacheRefreshed()方法的实现，但由于DiscoveryClient是Netflix的类，只发送了com.netflix.discovery.EurekaEvent，而CloudEurekaClient使用Spring的ApplicationEventPublisher，发送了HeartbeatEvent
创建DiscoveryClient的过程
DiscoveryClient构造方法
@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager,
EurekaClientConfig config,
AbstractDiscoveryClientOptionalArgs args,
Provider<BackupRegistry> backupRegistryProvider) {
/**
* AbstractDiscoveryClientOptionalArgs 是DiscoveryClient的可选参数，可理解为扩展点
* 包含healthCheckHandlerProvider、healthCheckCallbackProvider、eventListeners等
* spring cloud默认实现为MutableDiscoveryClientOptionalArgs，但此处相关成员变量赋值后认为空
*/
if (args != null) {
this.healthCheckHandlerProvider = args.healthCheckHandlerProvider;
this.healthCheckCallbackProvider = args.healthCheckCallbackProvider;
this.eventListeners.addAll(args.getEventListeners());
} else {
this.healthCheckCallbackProvider = null;
this.healthCheckHandlerProvider = 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(","));
// 如果 shouldFetchRegistry=true，注册netflix servo监控
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;
}
// 如果 shouldRegisterWithEureka=true，注册netflix servo监控
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());
// 如果既不要向eureka server注册，又不要获取服务列表，就什么都不用初始化
if (!config.shouldRegisterWithEureka() && !config.shouldFetchRegistry()) {
logger.info("Client configured to neither register nor query for data.");
scheduler = null;
heartbeatExecutor = null;
cacheRefreshExecutor = null;
eurekaTransport = null;
instanceRegionChecker = new InstanceRegionChecker(new PropertyBasedAzToRegionMapper(config), clientConfig.getRegion());
// This is a bit of hack to allow for existing code using DiscoveryManager.getInstance()
// to work with DI'd DiscoveryClient
DiscoveryManager.getInstance().setDiscoveryClient(this);
DiscoveryManager.getInstance().setEurekaClientConfig(config);
initTimestampMs = System.currentTimeMillis();
logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}",
initTimestampMs, this.getApplications().size());
return; // no need to setup up an network tasks and we are done
}
// 【重点】创建各种Executor 和 eurekaTransport、instanceRegionChecker
try {
// 执行定时任务的定时器，定时线程名为 DiscoveryClient-%d
// 在定时器中用于定时执行TimedSupervisorTask监督任务，监督任务会强制超时 和 记录监控数据
scheduler = Executors.newScheduledThreadPool(3,
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-%d")
.setDaemon(true)
.build());
// 执行heartbeat心跳任务的执行器，默认最大线程数=2，线程名为：DiscoveryClient-HeartbeatExecutor-%d
heartbeatExecutor = new ThreadPoolExecutor(
1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
.setDaemon(true)
.build()
); // use direct handoff
// 执行服务列表缓存刷新的执行器，默认最大线程数=2，线程名为：DiscoveryClient-CacheRefreshExecutor-%d
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();
// 初始化eurekaTransport在服务注册，获取服务列表时的client
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);
}
// 如果需要从eureka server获取服务列表，并且尝试fetchRegistry(false)失败，调用BackupRegistry
if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
fetchRegistryFromBackup();
}
// 【重点】初始化所有定时任务
initScheduledTasks();
// 添加servo监控
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());
}上面的DiscoveryClient构造方法代码比较多，但多数都是一些赋值，本次分析的重点在注释中已经标出，创建了各种Executor 和 eurekaTransport、instanceRegionChecker，之后又调用initScheduledTasks()方法初始化所有这些定时任务
【重点】initScheduledTasks() 初始化定时任务
/**
* Initializes all scheduled tasks.
*/
private void initScheduledTasks() {
// 1、如果要从Eureka Server获取服务列表
if (clientConfig.shouldFetchRegistry()) {
// registry cache refresh timer
// 从eureka服务器获取注册表信息的频率（默认30s）
// 同时也是单次获取服务列表的超时时间
int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
// 如果缓存刷新超时，下一次执行的delay最大是registryFetchIntervalSeconds的几倍（默认10），默认每次执行是上一次的2倍
int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
/**
* 【#### 执行CacheRefreshThread，服务列表缓存刷新任务 ####】
* 执行TimedSupervisorTask监督任务的定时器，具体执行器为cacheRefreshExecutor，任务为CacheRefreshThread
*/
scheduler.schedule(
new TimedSupervisorTask(
"cacheRefresh", //监控名
scheduler,
cacheRefreshExecutor,
registryFetchIntervalSeconds, //指定具体任务的超时时间
TimeUnit.SECONDS,
expBackOffBound,
new CacheRefreshThread()
),
registryFetchIntervalSeconds, TimeUnit.SECONDS);
}
// 2、如果要注册到Eureka Server
if (clientConfig.shouldRegisterWithEureka()) {
// 续租的时间间隔（默认30s）
int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
// 如果心跳任务超时，下一次执行的delay最大是renewalIntervalInSecs的几倍（默认10），默认每次执行是上一次的2倍
int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
logger.info("Starting heartbeat executor: " + "renew interval is: " + renewalIntervalInSecs);
// Heartbeat timer
/**
* 【#### 执行HeartbeatThread，发送心跳数据 ####】
* 执行TimedSupervisorTask监督任务的定时器，具体执行器为heartbeatExecutor，任务为HeartbeatThread
*/
scheduler.schedule(
new TimedSupervisorTask(
"heartbeat",
scheduler,
heartbeatExecutor,
renewalIntervalInSecs,
TimeUnit.SECONDS,
expBackOffBound,
new HeartbeatThread()
),
renewalIntervalInSecs, TimeUnit.SECONDS);
// InstanceInfo replicator
/**
* 【#### InstanceInfo复制器 ####】
* 启动后台定时任务scheduler，线程名为 DiscoveryClient-InstanceInfoReplicator-%d
* 默认每30s执行一次定时任务，查看Instance信息（DataCenterInfo、LeaseInfo、InstanceStatus）是否有变化
* 如果有变化，执行 discoveryClient.register()
*/
instanceInfoReplicator = new InstanceInfoReplicator(
this, //当前DiscoveryClient
instanceInfo, //当前实例信息
clientConfig.getInstanceInfoReplicationIntervalSeconds(),//InstanceInfo的复制间隔（默认30s）
2); // burstSize
/**
* 【StatusChangeListener 状态改变监听器】
*/
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);
}
//使用InstanceInfo复制器 scheduler.submit()一个Runnable任务
//后台马上执行 discoveryClient.register()
instanceInfoReplicator.onDemandUpdate();
}
};
/**
* 是否关注Instance状态变化，使用后台线程将状态同步到eureka server（默认true）
* 调用 ApplicationInfoManager#setInstanceStatus(status) 会触发
* 将 StatusChangeListener 注册到 ApplicationInfoManager
*/
if (clientConfig.shouldOnDemandUpdateStatusChange()) {
applicationInfoManager.registerStatusChangeListener(statusChangeListener);
}
// 启动InstanceInfo复制器
instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
}
// 当前服务实例不注册到Eureka Server
else {
logger.info("Not registering with Eureka server per configuration");
}
}总的来说initScheduledTasks()做了以下几件事：
- 如果shouldFetchRegistry=true，即要从Eureka Server获取服务列表
- 启动刷新服务列表定时线程（DiscoveryClient-CacheRefreshExecutor-%d），默认registryFetchIntervalSeconds=30s执行一次，任务为
CacheRefreshThread，即从Eureka Server获取服务列表，也刷新客户端缓存
- 启动刷新服务列表定时线程（DiscoveryClient-CacheRefreshExecutor-%d），默认registryFetchIntervalSeconds=30s执行一次，任务为
- 如果shouldRegisterWithEureka=true，即要注册到Eureka Server
- 启动heartbeat心跳定时线程（DiscoveryClient-HeartbeatExecutor-%d），默认renewalIntervalInSecs=30s续约一次，任务为
HeartbeatThread，即客户端向Eureka Server发送心跳 - 启动InstanceInfo复制器定时线程（DiscoveryClient-InstanceInfoReplicator-%d），开启定时线程检查当前Instance的DataCenterInfo、LeaseInfo、InstanceStatus，如果发现变更就执行
discoveryClient.register()，将实例信息同步到Server端
- 启动heartbeat心跳定时线程（DiscoveryClient-HeartbeatExecutor-%d），默认renewalIntervalInSecs=30s续约一次，任务为
Eureka Client复制InstanceInfo，发起注册
由创建DiscoveryClient的过程可知，创建了很多定时执行线程，如定时从Server端刷新服务列表的CacheRefreshThread，定时报心跳续约的HeartbeatThread，还有用于更新并复制本地实例状态到Server端的InstanceInfo复制器定时线程，而正是InstanceInfoReplicator#run()中的discoveryClient.register()发起了注册
那么怎么可以触发注册行为呢？
// InstanceInfoReplicator#run()
public void run() {
try {
/**
* 刷新 InstanceInfo
* 1、刷新 DataCenterInfo
* 2、刷新 LeaseInfo 租约信息
* 3、根据HealthCheckHandler获取InstanceStatus，并更新，如果状态发生变化会触发所有StatusChangeListener
*/
discoveryClient.refreshInstanceInfo();
// 如果isInstanceInfoDirty=true，返回dirtyTimestamp，否则是null
Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
if (dirtyTimestamp != null) {
discoveryClient.register(); //发起注册
instanceInfo.unsetIsDirty(dirtyTimestamp); //isInstanceInfoDirty置为false
}
}
catch (Throwable t) {
logger.warn("There was a problem with the instance info replicator", t);
}
finally { // 继续下次任务
Future next = scheduler.schedule(this, replicationIntervalSeconds, TimeUnit.SECONDS);
scheduledPeriodicRef.set(next);
}
}如上，先刷新InstanceInfo，刷新后如果发现有脏数据，即实例发生了变更，还未同步给Server的数据，就发起注册
那么在Eureka Client启动的这种场景下，怎样会触发有脏数据下的注册？
- 由InstanceInfoReplicator复制器的自动定时任务在刷新InstanceInfo时发现有脏数据，并更新
- InstanceInfoReplicator复制器提供
onDemandUpdate()按需更新方法，一旦调用，马上会submit()任务，其中会cancel自动更新任务，马上执行InstanceInfoReplicator#run()
InstanceInfoReplicator复制器自动定时更新
InstanceInfoReplicator复制器在启动创建DiscoveryClient时被创建并start()启动
// InstanceInfoReplicator#start()
public void start(int initialDelayMs) { // 默认40s
if (started.compareAndSet(false, true)) {
instanceInfo.setIsDirty(); // for initial register 初始化时会将instanceInfo设置为dirty
Future next = scheduler.schedule(this, initialDelayMs, TimeUnit.SECONDS);
scheduledPeriodicRef.set(next);
}
}所以当自动更新启动时会设置InstanceInfo为脏数据，因为要触发第一次向Server同步，那么在40s后会调用InstanceInfoReplicator#run()，假设InstanceInfo并没有其它变更，那么也会发起discoveryClient.register()
onDemandUpdate() 主动按需更新
目前只有在ApplicationInfoManager#setInstanceStatus()更新实例状态，且实例状态真的发生变更，触发StatusChangeListener状态变更监听器时，会调用onDemandUpdate马上submit任务执行InstanceInfoReplicator#run()，再发起注册
由于Spring Cloud默认是启用服务自动注册AutoServiceRegistration的，所以在EurekaClientAutoConfiguration自动配置时会注册服务自动注册相关组件（EurekaRegistration、EurekaServiceRegistry、EurekaAutoServiceRegistration），其中EurekaAutoServiceRegistration实现了Spring的SmartLifecycle接口，会在Spring容器refresh要完毕时触发生命周期方法start()，其中会使用EurekaServiceRegistry服务注册器注册EurekaRegistration这个本地实例信息
// EurekaServiceRegistry#register()
public void register(EurekaRegistration reg) {
maybeInitializeClient(reg);
if (log.isInfoEnabled()) {
log.info("Registering application " + reg.getInstanceConfig().getAppname()
+ " with eureka with status "
+ reg.getInstanceConfig().getInitialStatus());
}
// 设置初始化状态
reg.getApplicationInfoManager()
.setInstanceStatus(reg.getInstanceConfig().getInitialStatus());
if (reg.getHealthCheckHandler() != null) {
reg.getEurekaClient().registerHealthCheck(reg.getHealthCheckHandler());
}
}主要是设置初始化状态步骤，而EurekaInstanceConfigBean本地实例信息的initialStatus初始化状态为 InstanceStatus.UP，所以状态与new InstanceInfo()时的STARTING不同，发生了状态变更，触发在创建DiscoveryClient时设置的StatusChangeListener
...省略
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);
}
...省略其中会调用 InstanceInfoReplicator.onDemandUpdate() 实例信息复制器做按需更新，马上将UP状态更新/注册到Server端
DiscoveryClient#register() 注册
// DiscoveryClient#register()
boolean register() throws Throwable {
logger.info(PREFIX + appPathIdentifier + ": registering service...");
EurekaHttpResponse<Void> httpResponse;
try {
httpResponse = eurekaTransport.registrationClient.register(instanceInfo);
} catch (Exception e) {
logger.warn("{} - registration failed {}", PREFIX + appPathIdentifier, e.getMessage(), e);
throw e;
}
if (logger.isInfoEnabled()) {
logger.info("{} - registration status: {}", PREFIX + appPathIdentifier, httpResponse.getStatusCode());
}
return httpResponse.getStatusCode() == 204;
}如上，注册方法使用eurekaTransport的注册客户端registrationClient调用了register(instanceinfo)方法
EurekaTransport是DiscoveryClient的内部类，其中包含
- registrationClient 和 registrationClientFactory： 负责注册、续约相关工作的
EurekaHttpClient和EurekaHttpClientFactory的实现类 - queryClient 和 queryClientFactory： 负责获取Server端服务列表的
EurekaHttpClient和EurekaHttpClientFactory的实现类 - TransportClientFactory： 负责传输消息的客户端工厂（底层用于和Server交互的http框架是 Jersey，此处的工厂就和Jersey相关）
那么EurekaTransport的相关组件，尤其是registrationClient注册客户端是如何初始化的呢？
registrationClient - 服务注册相关的EurekaHttpClient
初始化是在DiscoveryClient的构造方法中
eurekaTransport = new EurekaTransport();
scheduleServerEndpointTask(eurekaTransport, args);主要是scheduleServerEndpointTask()方法
private void scheduleServerEndpointTask(EurekaTransport eurekaTransport,
AbstractDiscoveryClientOptionalArgs args) {
Collection<?> additionalFilters = args == null
? Collections.emptyList()
: args.additionalFilters;
EurekaJerseyClient providedJerseyClient = args == null
? null
: args.eurekaJerseyClient;
TransportClientFactories argsTransportClientFactories = null;
if (args != null && args.getTransportClientFactories() != null) {
argsTransportClientFactories = args.getTransportClientFactories();
}
// Ignore the raw types warnings since the client filter interface changed between jersey 1/2
@SuppressWarnings("rawtypes")
TransportClientFactories transportClientFactories = argsTransportClientFactories == null
? new Jersey1TransportClientFactories()
: argsTransportClientFactories;
// If the transport factory was not supplied with args, assume they are using jersey 1 for passivity
// 1、参数中是否提供了transportClientFactory的实现，没有就使用Jersey1TransportClientFactories
eurekaTransport.transportClientFactory = providedJerseyClient == null
? transportClientFactories.newTransportClientFactory(clientConfig, additionalFilters, applicationInfoManager.getInfo())
: transportClientFactories.newTransportClientFactory(additionalFilters, providedJerseyClient);
ApplicationsResolver.ApplicationsSource applicationsSource = new ApplicationsResolver.ApplicationsSource() {
@Override
public Applications getApplications(int stalenessThreshold, TimeUnit timeUnit) {
long thresholdInMs = TimeUnit.MILLISECONDS.convert(stalenessThreshold, timeUnit);
long delay = getLastSuccessfulRegistryFetchTimePeriod();
if (delay > thresholdInMs) {
logger.info("Local registry is too stale for local lookup. Threshold:{}, actual:{}",
thresholdInMs, delay);
return null;
} else {
return localRegionApps.get();
}
}
};
eurekaTransport.bootstrapResolver = EurekaHttpClients.newBootstrapResolver(
clientConfig,
transportConfig,
eurekaTransport.transportClientFactory,
applicationInfoManager.getInfo(),
applicationsSource
);
/**
* 是否要想Eureka Server注册
* 2、创建RegistrationClient用于注册的客户端及工厂，并设置到eurekaTransport
*/
if (clientConfig.shouldRegisterWithEureka()) {
EurekaHttpClientFactory newRegistrationClientFactory = null;
EurekaHttpClient newRegistrationClient = null;
try {
newRegistrationClientFactory = EurekaHttpClients.registrationClientFactory(
eurekaTransport.bootstrapResolver,
eurekaTransport.transportClientFactory,
transportConfig
);
newRegistrationClient = newRegistrationClientFactory.newClient();
} catch (Exception e) {
logger.warn("Transport initialization failure", e);
}
eurekaTransport.registrationClientFactory = newRegistrationClientFactory;
eurekaTransport.registrationClient = newRegistrationClient;
}
//
/**
* 是否要从Server端获取服务列表
* 3、创建QueryClient用于查询服务列表的客户端及工厂，并设置到eurekaTransport
*/
// new method (resolve from primary servers for read)
// Configure new transport layer (candidate for injecting in the future)
if (clientConfig.shouldFetchRegistry()) {
EurekaHttpClientFactory newQueryClientFactory = null;
EurekaHttpClient newQueryClient = null;
try {
newQueryClientFactory = EurekaHttpClients.queryClientFactory(
eurekaTransport.bootstrapResolver,
eurekaTransport.transportClientFactory,
clientConfig,
transportConfig,
applicationInfoManager.getInfo(),
applicationsSource
);
newQueryClient = newQueryClientFactory.newClient();
} catch (Exception e) {
logger.warn("Transport initialization failure", e);
}
eurekaTransport.queryClientFactory = newQueryClientFactory;
eurekaTransport.queryClient = newQueryClient;
}
}所以，下面就是逐层深入分析RegistrationClient用于注册的客户端及工厂是如何创建的？
由于RegistrationClient其实是一种EurekaHttpClient，而EurekaHttpClient是接口，其实现类很多
查看源码发现，Netflix采用的是 Factory工厂 + 代理 的模式，从最外层创建的EurekaHttpClient工厂包含一个成员变量是另一个代理的EurekaHttpClient工厂，每个工厂生成的EurekaHttpClient功能不一样，在从外层执行一个操作时，最外层的工厂执行其相关功能后，使用代理的工厂新建EurekaHttpClient实例，再调用其相同的方法，也实现这个EurekaHttpClient的相关功能，就这样逐层深入，各司其职后，最后使用Jersey发送POST请求到Eureka Server发起注册，而这些EurekaHttpClient都是在com.netflix.discovery.shared.transport.decoratorEurekaHttpClient的包装类的包下的，由外到内大致是：
- SessionedEurekaHttpClient： 强制在一定时间间隔后重连EurekaHttpClient，防止永远只连接特定Eureka Server，反过来保证了在Server端集群拓扑发生变化时的负载重分配
- RetryableEurekaHttpClient： 带有重试功能，默认最多3次，在配置的所有候选Server地址中尝试请求，成功重用，失败会重试另一Server，并维护隔离清单，下次跳过，当隔离数量达到阈值，清空隔离清单，重新开始
- RedirectingEurekaHttpClient： Server端返回302重定向时，客户端shutdown原EurekaHttpClient，根据response header中的Location新建EurekaHttpClient
- MetricsCollectingEurekaHttpClient： 统计收集Metrics信息
- JerseyApplicationClient： AbstractJerseyEurekaHttpClient的子类
- AbstractJerseyEurekaHttpClient： 底层实现通过Jersery注册、发心跳等的核心类
- jerseyClient： Jersery客户端
- AbstractJerseyEurekaHttpClient： 底层实现通过Jersery注册、发心跳等的核心类
- JerseyApplicationClient： AbstractJerseyEurekaHttpClient的子类
- MetricsCollectingEurekaHttpClient： 统计收集Metrics信息
- RedirectingEurekaHttpClient： Server端返回302重定向时，客户端shutdown原EurekaHttpClient，根据response header中的Location新建EurekaHttpClient
- RetryableEurekaHttpClient： 带有重试功能，默认最多3次，在配置的所有候选Server地址中尝试请求，成功重用，失败会重试另一Server，并维护隔离清单，下次跳过，当隔离数量达到阈值，清空隔离清单，重新开始
SessionedEurekaHttpClient - 定时重连
// SessionedEurekaHttpClient#execute()
@Override
protected <R> EurekaHttpResponse<R> execute(RequestExecutor<R> requestExecutor) {
long now = System.currentTimeMillis();
long delay = now - lastReconnectTimeStamp;
// 如果上次重连时间到现在已经超过了currentSessionDurationMs，关闭当前EurekaHttpClient
if (delay >= currentSessionDurationMs) {
logger.debug("Ending a session and starting anew");
lastReconnectTimeStamp = now;
currentSessionDurationMs = randomizeSessionDuration(sessionDurationMs);
TransportUtils.shutdown(eurekaHttpClientRef.getAndSet(null));
}
// 如果EurekaHttpClient为空，clientFactory.newClient()重建
EurekaHttpClient eurekaHttpClient = eurekaHttpClientRef.get();
if (eurekaHttpClient == null) {
eurekaHttpClient = TransportUtils.getOrSetAnotherClient(eurekaHttpClientRef, clientFactory.newClient());
}
// 继续执行后续
return requestExecutor.execute(eurekaHttpClient);
}RetryableEurekaHttpClient - 候选范围内失败重试
// RetryableEurekaHttpClient#execute()
@Override
protected <R> EurekaHttpResponse<R> execute(RequestExecutor<R> requestExecutor) {
List<EurekaEndpoint> candidateHosts = null;
int endpointIdx = 0;
// 最多重试numberOfRetries（默认：3）
for (int retry = 0; retry < numberOfRetries; retry++) {
EurekaHttpClient currentHttpClient = delegate.get();//从AtomicReference<EurekaHttpClient>获取当前EurekaHttpClient
EurekaEndpoint currentEndpoint = null;
if (currentHttpClient == null) {
if (candidateHosts == null) {
candidateHosts = getHostCandidates(); //返回候选集合 排除 已经失败隔离的Host集合
if (candidateHosts.isEmpty()) {
throw new TransportException("There is no known eureka server; cluster server list is empty");
}
}
if (endpointIdx >= candidateHosts.size()) {
throw new TransportException("Cannot execute request on any known server");
}
// 根据当前的下标获取Endpoint，并新建 JerseyClient
currentEndpoint = candidateHosts.get(endpointIdx++);
currentHttpClient = clientFactory.newClient(currentEndpoint);
}
try {
// 继续后续执行
EurekaHttpResponse<R> response = requestExecutor.execute(currentHttpClient);
// 如果根据当前操作类型 和 返回状态码，满足状态计算器，记录currentHttpClient可用，下次继续使用
// 返回状态码是：200、300、302，或者Register、SendHeartBeat情况下是404
if (serverStatusEvaluator.accept(response.getStatusCode(), requestExecutor.getRequestType())) {
delegate.set(currentHttpClient);
if (retry > 0) {
logger.info("Request execution succeeded on retry #{}", retry);
}
return response;
}
logger.warn("Request execution failure with status code {}; retrying on another server if available", response.getStatusCode());
}
catch (Exception e) {
logger.warn("Request execution failed with message: {}", e.getMessage()); // just log message as the underlying client should log the stacktrace
}
// Connection error or 5xx from the server that must be retried on another server
// 请求失败 或 报5xx错误，将delegate清空，重试另一个Server，并将当前Endpoint放到隔离集合
delegate.compareAndSet(currentHttpClient, null);
if (currentEndpoint != null) {
quarantineSet.add(currentEndpoint);
}
}
// 多次重试后仍无法成功返回结果，上抛异常
throw new TransportException("Retry limit reached; giving up on completing the request");
}
//########## RetryableEurekaHttpClient#getHostCandidates()
// 返回 所有候选的Host节点数据 与 隔离集合 的数据差集
private List<EurekaEndpoint> getHostCandidates() {
List<EurekaEndpoint> candidateHosts = clusterResolver.getClusterEndpoints(); //所有候选节点数据
quarantineSet.retainAll(candidateHosts); //确保quarantineSet隔离集合中的数据都在candidateHosts中
//当candidateHosts发生变化时也能及时清理quarantineSet隔离集合
// If enough hosts are bad, we have no choice but start over again
// 默认：0.66百分比
int threshold = (int) (candidateHosts.size() * transportConfig.getRetryableClientQuarantineRefreshPercentage());
// 隔离集合为空
if (quarantineSet.isEmpty()) {
// no-op
}
// 隔离数据已经大于阀值，不得已要重新开始，清空隔离集合
else if (quarantineSet.size() >= threshold) {
logger.debug("Clearing quarantined list of size {}", quarantineSet.size());
quarantineSet.clear();
}
// 隔离集合不为空，也不大于阀值，排除隔离集合中的Endpoint后返回
else {
List<EurekaEndpoint> remainingHosts = new ArrayList<>(candidateHosts.size());
for (EurekaEndpoint endpoint : candidateHosts) {
if (!quarantineSet.contains(endpoint)) {
remainingHosts.add(endpoint);
}
}
candidateHosts = remainingHosts;
}
return candidateHosts;
}
//########## ServerStatusEvaluators#LEGACY_EVALUATOR
// Eureka Server返回状态的计算器，计算不同场景下的不同状态码是否代表成功
private static final ServerStatusEvaluator LEGACY_EVALUATOR = new ServerStatusEvaluator() {
@Override
public boolean accept(int statusCode, RequestType requestType) {
if (statusCode >= 200 && statusCode < 300 || statusCode == 302) {
return true;
} else if (requestType == RequestType.Register && statusCode == 404) {
return true;
} else if (requestType == RequestType.SendHeartBeat && statusCode == 404) {
return true;
} else if (requestType == RequestType.Cancel) { // cancel is best effort
return true;
} else if (requestType == RequestType.GetDelta && (statusCode == 403 || statusCode == 404)) {
return true;
}
return false;
}
};RedirectingEurekaHttpClient - 按Server端要求重定向到新Server
//########## RedirectingEurekaHttpClient#executeOnNewServer
// Server端返回302重定向时，客户端shutdown原EurekaHttpClient，根据response header中的Location新建EurekaHttpClient
private <R> EurekaHttpResponse<R> executeOnNewServer(RequestExecutor<R> requestExecutor,
AtomicReference<EurekaHttpClient> currentHttpClientRef) {
URI targetUrl = null;
// 最多重定向默认10次
for (int followRedirectCount = 0; followRedirectCount < MAX_FOLLOWED_REDIRECTS; followRedirectCount++) {
EurekaHttpResponse<R> httpResponse = requestExecutor.execute(currentHttpClientRef.get());
// 如果返回的不是302重定向，返回response
if (httpResponse.getStatusCode() != 302) {
if (followRedirectCount == 0) {
logger.debug("Pinning to endpoint {}", targetUrl);
} else {
logger.info("Pinning to endpoint {}, after {} redirect(s)", targetUrl, followRedirectCount);
}
return httpResponse;
}
// 从response中获取Location，用于重建EurekaHttpClient
targetUrl = getRedirectBaseUri(httpResponse.getLocation());
if (targetUrl == null) {
throw new TransportException("Invalid redirect URL " + httpResponse.getLocation());
}
currentHttpClientRef.getAndSet(null).shutdown();
currentHttpClientRef.set(factory.newClient(new DefaultEndpoint(targetUrl.toString())));
}
String message = "Follow redirect limit crossed for URI " + serviceEndpoint.getServiceUrl();
logger.warn(message);
throw new TransportException(message);
}MetricsCollectingEurekaHttpClient - 统计收集执行情况
// MetricsCollectingEurekaHttpClient#execute()
protected <R> EurekaHttpResponse<R> execute(RequestExecutor<R> requestExecutor) {
EurekaHttpClientRequestMetrics requestMetrics = metricsByRequestType.get(requestExecutor.getRequestType());
Stopwatch stopwatch = requestMetrics.latencyTimer.start(); //统计执行延时
try {
EurekaHttpResponse<R> httpResponse = requestExecutor.execute(delegate);
requestMetrics.countersByStatus.get(mappedStatus(httpResponse)).increment(); //按状态统计
return httpResponse;
} catch (Exception e) {
requestMetrics.connectionErrors.increment(); //统计错误
exceptionsMetric.count(e); //按异常名统计
throw e;
} finally {
stopwatch.stop();
}
}AbstractJerseyEurekaHttpClient - 底层通过Jersery发送注册、心跳请求
public abstract class AbstractJerseyEurekaHttpClient implements EurekaHttpClient {
protected final Client jerseyClient; //真正处理请求的Jersery客户端
protected final String serviceUrl; //连接的Server端地址
protected AbstractJerseyEurekaHttpClient(Client jerseyClient, String serviceUrl) {
this.jerseyClient = jerseyClient;
this.serviceUrl = serviceUrl;
logger.debug("Created client for url: {}", serviceUrl);
}
/**
* 注册方法
*/
@Override
public EurekaHttpResponse<Void> register(InstanceInfo info) {
String urlPath = "apps/" + info.getAppName(); //请求Eureka Server的【/apps/应用名】接口地址
ClientResponse response = null;
try {
Builder resourceBuilder = jerseyClient.resource(serviceUrl).path(urlPath).getRequestBuilder();
addExtraHeaders(resourceBuilder);
response = resourceBuilder
.header("Accept-Encoding", "gzip")
.type(MediaType.APPLICATION_JSON_TYPE)
.accept(MediaType.APPLICATION_JSON)
.post(ClientResponse.class, info); //实例InstanceInfo数据，通过Post请求body发过去
return anEurekaHttpResponse(response.getStatus()).headers(headersOf(response)).build();
}
finally {
if (logger.isDebugEnabled()) {
logger.debug("Jersey HTTP POST {}/{} with instance {}; statusCode={}", serviceUrl, urlPath, info.getId(),
response == null ? "N/A" : response.getStatus());
}
if (response != null) {
response.close();
}
}
}
...省略Eureka Server接收到的注册请求详情
经过上面的步骤，客户端已经可以通过Jersery发送Http请求给Eureka Server端注册，具体请求如下：
POST /eureka/apps/应用名 HTTP/1.1
Accept-Encoding: gzip
Content-Type: application/json
Accept: application/json
DiscoveryIdentity-Name: DefaultClient
DiscoveryIdentity-Version: 1.4
DiscoveryIdentity-Id: 192.168.70.132
Transfer-Encoding: chunked
Host: localhost:8001
Connection: Keep-Alive
User-Agent: Java-EurekaClient/v1.6.2
1a0
{"instance":{
"instanceId":"192.168.70.132:应用名:10001",
"hostName":"192.168.70.132",
"app":"应用名",
"ipAddr":"192.168.70.132",
"status":"UP",
"overriddenstatus":"UNKNOWN",
"port": { "\(":10001, "@enabled" : "true" }, "securePort": { "\)":443, "@enabled" : "false"},
"countryId":1,
"dataCenterInfo":{"@class":"com.netflix.appinfo.InstanceInfo$DefaultDataCenterInfo",
"name":"MyOwn"
}
Eureka Client注册流程总结
EurekaAutoServiceRegistration#start()： 实现Spring的SmartLifecycle，在Spring容器refresh()最后一步finishRefresh()会调用生命周期的start()方法
EurekaServiceRegistry#register(EurekaRegistration)： 使用服务注册器注册服务信息
ApplicationInfoManager#setInstanceStatus(初始状态)： 应用实例信息管理器更新初始状态为 UP
StatusChangeListener： 触发实例状态监听（此Listener是在DiscoveryClient#initScheduledTasks()方法中设置的）
InstanceInfoReplicator.onDemandUpdate()： 实例状态复制器执行按需状态更新
DiscoveryClient#register()： DiscoveryClient发起注册实例信息
EurekaHttpClientDecorator#execute()： 执行EurekaHttpClient的装饰类，实现其各自功能
- JerseyApplicationClient#register()： 封装注册请求数据
- JerseyClient发送Post注册请求
- JerseyApplicationClient#register()： 封装注册请求数据