EurekaClien
EurekaClient 为了简化开发人员的工作量，将很多与EurekaServer交互的工作隐藏起来，自主完成。具体完成的工作分为三个阶段， 应用启动阶段,执行阶段, 销毁阶段. 各阶段的工作如下:
应用启动阶段
1、 读取与EurekaServer交互的配置信息,封装成EurekaClientConfig；
2、 读取自身服务实例配置信息,封装成EurekalnstanceConfig；
3、 从Eurekaserver拉取注册表信息并缓存到本地；
4、 服务注册；
5、 初始化发送心跳、缓存刷新(拉取注册表信息更新本地缓存)和按需注册(监控服务实例信息变化,决定是否重新发起注册,更新注册表中的服务实例元数据)定时任务；
应用执行阶段
1、 定时发送心跳到EurekaServer中维持在注册表的租约；
2、 定时从EurekaServer中拉取注册表信息,更新本地注册表缓存；
3、 监控应用自身信息变化,若发生变化,需要重新发起服务注册；
应用销毁阶段
从 Eureka Server注销自身服务实例
下面让我们按阶段来分析一下源码
应用启动阶段与运行阶段分析
Eureka Client通过Starter的方式引人依赖, Spring Boot将会为项目使用以下的自动配置类
- EurekaClientAutoConfiguration：EurekeClient 自动配置类,负责Eureka关键Beans的配置和初始化,如AppplicationInfoManager和 EurekaClientConfig等。
- RibbonEurekaAutoConfiguration: Ribbon负载均衡相关配置。
- EurekaDiscoveryClientConfiguration: 配置自动注册和应用的健康检查器。
查看源码: 在classpath下查找 Spring-cloud-netflix-eureka-client.xx.jar 下 META-INF 下的Spring.factories配置信息.
读取应用自身配置
通过 EurekaClientAutoConfiguration配置类, Spring boot帮助 Eureka Client完成很多必要Bean的属性读取和配置
- EurekaClientConfig: 封装 Eureka Client与 Eureka Server交互所需要的配置信息。 Spring Cloud为其提供了一个默认配置类的EurekaClientConfigBean,可以在配置文件中通过前缀 eureka.client属性名进行属性覆盖
- ApplicationInfoManager : 作为应用信息管理器,管理服务实例的信息类 InstanceInfo和服务实例的配置信息类 EurekaInstanceConfig
- InstanceInfo: 封装将被发送到 Eureka Server进行服务注册的服务实例元数据。它在Eurek Server的注册表中代表一个服务实例,其他服务实例可以通过 Instancelnfo了解该服务的相关信息从而发起服务请求
- EurekaInstanceConfig: 封装EurekaClient自身服务实例的配置信息,主要用于构建InstanceInfo通常这些信息在配置文件中的eureka.instance前缀下进行设置, SpringCloud通过EurekalnstanceConfigBean配置类提供了默认配置
- DiscoveryClient: Spring Cloud中定义用来服务发现的客户端接口, 对于DiscoveryClient可以具体查看 EurekaDiscoveryClient，EurekaDiscoveryClient又借助EurekaClient来实现
@Bean //由spring 托管
public DiscoveryClient discoveryClient(EurekaClient client,
EurekaClientConfig clientConfig) {
return new EurekaDiscoveryClient(client, clientConfig);
}
在新版的springcloud中( 2021版）这个类被它的一个子类 CloudEurekaClient代替了。
@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, @Autowired(required = false) HealthCheckHandler healthCheckHandler) {
ApplicationInfoManager appManager;
if (AopUtils.isAopProxy(manager)) {
appManager = (ApplicationInfoManager)ProxyUtils.getTargetObject(manager);
} else {
appManager = manager;
}
//这个类是 DiscoveryClient的子类，请跟踪这个类
CloudEurekaClient cloudEurekaClient = new CloudEurekaClient(appManager, config, this.optionalArgs, this.context);
cloudEurekaClient.registerHealthCheck(healthCheckHandler);
return cloudEurekaClient;
}
另外在netflix包里面还有一个DiscoveryClient，按名字翻译其实就是服务发现客户端，他是整个EurekaClient的核心，是与EurekaServer进行交互的核心所在.
客户端的类结构:
下面来查看一下 eureka-client.xxx.jar下的 DiscoveryClient是开始时如何运行服务的.
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
Provider<BackupRegistry> backupRegistryProvider) {
if (args != null) {
this.healthCheckHandlerProvider = args.healthCheckHandlerProvider;
this.healthCheckCallbackProvider = args.healthCheckCallbackProvider;
this.eventListeners.addAll(args.getEventListeners());
this.preRegistrationHandler = args.preRegistrationHandler;
} else {
this.healthCheckCallbackProvider = null;
this.healthCheckHandlerProvider = null;
this.preRegistrationHandler = null;
}
this.applicationInfoManager = applicationInfoManager;
InstanceInfo myInfo = applicationInfoManager.getInfo();
clientConfig = config;
staticClientConfig = clientConfig;
transportConfig = config.getTransportConfig();
instanceInfo = myInfo;
if (myInfo != null) {
appPathIdentifier = instanceInfo.getAppName() + "/" + instanceInfo.getId();
} else {
logger.warn("Setting instanceInfo to a passed in null value");
}
//传入BackupRegistry（NotImplementedRegistryImpl）备份注册中心
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(","));
//从eureka server拉起注册表信息 对应配置项-> eureka.client.fetch-register
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;
}
// 当前的客户端是否应该注册到erueka中 对应配置项-> eureka.client.register-with-eureka
if (config.shouldRegisterWithEureka()) {
this.heartbeatStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRATION_PREFIX + "lastHeartbeatSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
} else {
this.heartbeatStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;
}
logger.info("Initializing Eureka in region {}", clientConfig.getRegion());
//如果既不需要注册，也不需要拉去数据，直接返回,初始结束
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 {
//线程池大小为2，一个用户发送心跳，另外个缓存刷新
// default size of 2 - 1 each for heartbeat and cacheRefresh
scheduler = Executors.newScheduledThreadPool(2,
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-%d")
.setDaemon(true)
.build());
heartbeatExecutor = new ThreadPoolExecutor(
1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
.setDaemon(true)
.build()
); // use direct handoff
cacheRefreshExecutor = new ThreadPoolExecutor(
1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
.setDaemon(true)
.build()
); // use direct handoff
//初始化client与server交互的jersey客户端
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);
}
//拉取注册表的信息
if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
fetchRegistryFromBackup();
}
//将服务实例进行注册
// 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) {
logger.error("Registration error at startup: {}", th.getMessage());
throw new IllegalStateException(th);
}
}
// finally, init the schedule tasks (e.g. cluster resolvers, heartbeat, instanceInfo replicator, fetch
//初始心跳定时任务，缓存刷新
initScheduledTasks();
try {
Monitors.registerObject(this);
} catch (Throwable e) {
logger.warn("Cannot register timers", e);
}
// This is a bit of hack to allow for existing code using DiscoveryManager.getInstance()
// to work with DI'd DiscoveryClient
DiscoveryManager.getInstance().setDiscoveryClient(this);
DiscoveryManager.getInstance().setEurekaClientConfig(config);
initTimestampMs = System.currentTimeMillis();
logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}",
initTimestampMs, this.getApplications().size());
}
DiscoveryClient构造函数做的事情:
1、 相关配置赋值；
2、 备份注册中心的初始化，实际什么事都没做；
3、 拉取Server注册表中的信息；
4、 注册前的预处理；
5、 向Server注册自身；
6、 初始心跳定时任务，缓存刷新等定时任务；
下面抽取构造函数中的几个
重要步骤重点分析一下:
拉取Server注册表中的信息
从这一句开始:
if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false))
//拉取注册信息，拉取的方法分为全量拉取和增量拉取.
private boolean fetchRegistry(boolean forceFullRegistryFetch) {
Stopwatch tracer = FETCH_REGISTRY_TIMER.start();
try {
// If the delta is disabled or if it is the first time, get all
// applications
//如果增量拉取被禁止,则全量拉取
Applications applications = getApplications();
if (clientConfig.shouldDisableDelta()
|| (!Strings.isNullOrEmpty(clientConfig.getRegistryRefreshSingleVipAddress()))
|| forceFullRegistryFetch
|| (applications == null) //如果是第一次拉取，applications为null,则全量拉取
|| (applications.getRegisteredApplications().size() == 0)
|| (applications.getVersion() == -1)) //Client application does not have latest library supporting delta
{
//全量拉取
getAndStoreFullRegistry();
} else {
//增量拉取
getAndUpdateDelta(applications);
}
applications.setAppsHashCode(applications.getReconcileHashCode());
//打印注册表上所有服务实例信息
logTotalInstances();
} catch (Throwable e) {
logger.error(PREFIX + "{} - was unable to refresh its cache! status = {}", appPathIdentifier, e.getMessage(), e);
return false;
} finally {
if (tracer != null) {
tracer.stop();
}
}
onCacheRefreshed();
// Update remote status based on refreshed data held in the cache
updateInstanceRemoteStatus();
// registry was fetched successfully, so return true
return true;
}
全量拉取
一般只有发生在第一次拉去注册表信息的时候，全量拉取调用 getAndStoreFullRegistry()方法
private void getAndStoreFullRegistry() throws Throwable {
//拉取注册表的版本信息
long currentUpdateGeneration = fetchRegistryGeneration.get();
logger.info("Getting all instance registry info from the eureka server");
Applications apps = null;
EurekaHttpResponse<Applications> httpResponse = clientConfig.getRegistryRefreshSingleVipAddress() == null
? eurekaTransport.queryClient.getApplications(remoteRegionsRef.get())
: eurekaTransport.queryClient.getVip(clientConfig.getRegistryRefreshSingleVipAddress(), remoteRegionsRef.get()); //eurekaTransport是客户端与服务端的联接对象
//拉取成功,则保存信息到 apps中
if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
apps = httpResponse.getEntity();
}
logger.info("The response status is {}", httpResponse.getStatusCode());
if (apps == null) {
logger.error("The application is null for some reason. Not storing this information");
} else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) { //拉取成功，保存
localRegionApps.set(this.filterAndShuffle(apps));
logger.debug("Got full registry with apps hashcode {}", apps.getAppsHashCode());
} else {
logger.warn("Not updating applications as another thread is updating it already");
}
}
增量拉取
对应的方法为: getAndUpdateDelta(applications)
private void getAndUpdateDelta(Applications applications) throws Throwable {
long currentUpdateGeneration = fetchRegistryGeneration.get(); //注册表版本,用于CAS操作
//拉取信息
Applications delta = null;
EurekaHttpResponse<Applications> httpResponse = eurekaTransport.queryClient.getDelta(remoteRegionsRef.get());
if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
delta = httpResponse.getEntity();
}
//如果拉取失败进行全量拉取
if (delta == null) {
logger.warn("The server does not allow the delta revision to be applied because it is not safe. "
+ "Hence got the full registry.");
getAndStoreFullRegistry();
} else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
logger.debug("Got delta update with apps hashcode {}", delta.getAppsHashCode());
String reconcileHashCode = "";
if (fetchRegistryUpdateLock.tryLock()) {
try {
//更新本地缓存
updateDelta(delta);
reconcileHashCode = getReconcileHashCode(applications);
} finally {
fetchRegistryUpdateLock.unlock();
}
} else {
logger.warn("Cannot acquire update lock, aborting getAndUpdateDelta");
}
// There is a diff in number of instances for some reason
if (!reconcileHashCode.equals(delta.getAppsHashCode()) || clientConfig.shouldLogDeltaDiff()) {
reconcileAndLogDifference(delta, reconcileHashCode); // this makes a remoteCall
}
} else {
logger.warn("Not updating application delta as another thread is updating it already");
logger.debug("Ignoring delta update with apps hashcode {}, as another thread is updating it already", delta.getAppsHashCode());
}
}
向服务器注册
从这句代码开始
if (clientConfig.shouldRegisterWithEureka() && clientConfig.shouldEnforceRegistrationAtInit()) {
try {
if (!register() ) { //开始完成注册
throw new IllegalStateException("Registration error at startup. Invalid server response.");
}
} catch (Throwable th) {
logger.error("Registration error at startup: {}", th.getMessage());
throw new IllegalStateException(th);
}
}
register()方法负责服务的注册
boolean register() throws Throwable {
logger.info(PREFIX + "{}: registering service...", appPathIdentifier);
EurekaHttpResponse<Void> httpResponse;
try {
//把自身的实例发送给服务端
httpResponse = eurekaTransport.registrationClient.register(instanceInfo);
} catch (Exception e) {
logger.warn(PREFIX + "{} - registration failed {}", appPathIdentifier, e.getMessage(), e);
throw e;
}
// 在http的响应状态码中, 204意思等同于请求执行成功，但是没有数据，浏览器不用刷新页面.也不用导向新的页面
return httpResponse.getStatusCode() == 204;
}
定时任务: initScheduledTasks()是负责定时任务的相关方法。
从这一句开始
// finally, init the schedule tasks (e.g. cluster resolvers, heartbeat, instanceInfo replicator, fetch
initScheduledTasks();
private void initScheduledTasks() {
if (clientConfig.shouldFetchRegistry()) {
// 拉取服务默认30秒，eureka.client.register-fetch-interval-seconds
int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
//更新缓存
int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
scheduler.schedule(
new TimedSupervisorTask(
"cacheRefresh",
scheduler,
cacheRefreshExecutor,
registryFetchIntervalSeconds,
TimeUnit.SECONDS,
expBackOffBound,
new CacheRefreshThread()
),
registryFetchIntervalSeconds, TimeUnit.SECONDS);
}
if (clientConfig.shouldRegisterWithEureka()) {
int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
logger.info("Starting heartbeat executor: " + "renew interval is: {}", renewalIntervalInSecs);
// 心跳服务，默认30秒
scheduler.schedule(
new TimedSupervisorTask(
"heartbeat",
scheduler,
heartbeatExecutor,
renewalIntervalInSecs,
TimeUnit.SECONDS,
expBackOffBound,
new HeartbeatThread()
),
renewalIntervalInSecs, TimeUnit.SECONDS);
// InstanceInfo replicator
instanceInfoReplicator = new InstanceInfoReplicator(
this,
instanceInfo,
clientConfig.getInstanceInfoReplicationIntervalSeconds(),
2); // burstSize
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);
}
instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
} else {
logger.info("Not registering with Eureka server per configuration");
}
}
以上完成了 DiscoveryClient的构造函数的分析，下面来看一下Client如何完成服务下线操作的. 请查看 com.netflix.discovery.DiscoveryClient#shutdown.
@PreDestroy // bean销毁前调用的函数
@Override
public synchronized void shutdown() {
if (isShutdown.compareAndSet(false, true)) {
logger.info("Shutting down DiscoveryClient ...");
if (statusChangeListener != null && applicationInfoManager != null) {
//注销状态监听器
applicationInfoManager.unregisterStatusChangeListener(statusChangeListener.getId());
}
//取消定时任务
cancelScheduledTasks();
// If APPINFO was registered
if (applicationInfoManager != null
&& clientConfig.shouldRegisterWithEureka()
&& clientConfig.shouldUnregisterOnShutdown()) {
applicationInfoManager.setInstanceStatus(InstanceStatus.DOWN);
unregister();
}
//关闭与server连接的客户端
if (eurekaTransport != null) {
eurekaTransport.shutdown();
}
//关闭相关监控
heartbeatStalenessMonitor.shutdown();
registryStalenessMonitor.shutdown();
logger.info("Completed shut down of DiscoveryClient");
}
}
EurekaClient其它功能的源码解析后续再加吧.
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来源：https://blog.csdn.net/zhangyingchengqi/category_10464123.html