Eureka源码解析（二）
服务注册触发路径
这个动作在spring boot的启动方法中的refreshContext中完成
SpringApplication.run() -> this.refreshContext(context); -> this.refresh(context); -> ServletWebServerApplicationContext.refresh() -> this.finishRefresh();
-> AbstractApplicationContext.finishRefresh->DefaultLifecycleProcessor.onRefresh()-> this.startBeans->this.start()->this.doStart()
finishRefresh
这个方法，从名字上可以看到它是用来体现完成刷新的操作，也就是刷新完成之后要做的后置的操作。它主要做几个事情
- 清空缓存
- 初始化一个LifecycleProcessor，在Spring启动的时候启动bean，在spring结束的时候销毁bean
- 调用LifecycleProcessor的onRefresh方法，启动实现了Lifecycle接口的bean
- 发布ContextRefreshedEvent
- 注册MBean，通过JMX进行监控和管理
protected void finishRefresh() {
// Clear context-level resource caches (such as ASM metadata from scanning).
clearResourceCaches();
// Initialize lifecycle processor for this context.
initLifecycleProcessor();
// Propagate refresh to lifecycle processor first.
getLifecycleProcessor().onRefresh();
// Publish the final event.
publishEvent(new ContextRefreshedEvent(this));
// Participate in LiveBeansView MBean, if active.
LiveBeansView.registerApplicationContext(this);
}
在这个方法中，重点关注 getLifecycleProcessor().onRefresh() ，它是调用生命周期处理器的onrefresh方法，找到SmartLifecycle接口的所有实现类并调用start方法。
后续的调用链路为：DefaultLifecycleProcessor.startBean -> start() -> doStart() -> bean.start()
SmartLifeCycle
SmartLifeCycle是一个接口，当Spring容器加载完所有的Bean并且初始化之后，会继续回调实现了SmartLifeCycle接口的类中对应的方法，比如（start）
SmartLifeCycle的理解：
@Component
public class MyLifecycleProcessor implements SmartLifecycle {
@Override
public void start() {
System.out.println("start");
}
@Override
public void stop() {
System.out.println("stop");
}
@Override
public boolean isRunning() {
return false;
}
}
启动spring boot应用后，可以看到控制台输出了 start 字符串。在DefaultLifecycleProcessor.startBeans方法上加一个debug，可以很明显的看到我们自己定义的MyLifecycleProcessor被扫描到了，并且最后会调用该bean的start方法。
在startBeans方法中，可以看到它首先会获得所有实现了SmartLifeCycle的Bean，然后会循环调用实现了SmartLifeCycle的bean的start方法，代码如下。
private void startBeans(boolean autoStartupOnly) {
Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans();
Map<Integer, LifecycleGroup> phases = new HashMap<>();
lifecycleBeans.forEach((beanName, bean) -> {
if (!autoStartupOnly || (bean instanceof SmartLifecycle && ((SmartLifecycle) bean).isAutoStartup())) {
int phase = getPhase(bean);
LifecycleGroup group = phases.get(phase);
if (group == null) {
group = new LifecycleGroup(phase, this.timeoutPerShutdownPhase, lifecycleBeans, autoStartupOnly);
phases.put(phase, group);
}
group.add(beanName, bean);
}
});
if (!phases.isEmpty()) {
List<Integer> keys = new ArrayList<>(phases.keySet());
Collections.sort(keys);
for (Integer key : keys) {
phases.get(key).start();
}
}
}
doStart()
private void doStart(Map<String, ? extends Lifecycle> lifecycleBeans, String beanName, boolean autoStartupOnly) {
Lifecycle bean = lifecycleBeans.remove(beanName);
if (bean != null && bean != this) {
String[] dependenciesForBean = getBeanFactory().getDependenciesForBean(beanName);
for (String dependency : dependenciesForBean) {
doStart(lifecycleBeans, dependency, autoStartupOnly);
}
if (!bean.isRunning() &&
(!autoStartupOnly || !(bean instanceof SmartLifecycle) || ((SmartLifecycle) bean).isAutoStartup())) {
if (logger.isTraceEnabled()) {
logger.trace("Starting bean '" + beanName + "' of type [" + bean.getClass().getName() + "]");
}
try {
//此时 Bean的实例是EurekaAutoServiceRegistration
bean.start();
}
catch (Throwable ex) {
throw new ApplicationContextException("Failed to start bean '" + beanName + "'", ex);
}
if (logger.isDebugEnabled()) {
logger.debug("Successfully started bean '" + beanName + "'");
}
}
}
}
此时，bean.start()，调用的是EurekaAutoServiceRegistration中的start方法，因为很显然，它实现了SmartLifeCycle接口。
public class EurekaAutoServiceRegistration implements AutoServiceRegistration, SmartLifecycle, Ordered, SmartApplicationListener {
@Override
public void start() {
//...
}
}
在start方法中，我们可以看到 this.serviceRegistry.register 这个方法，它实际上就是发起服务注册的机制。
此时this.serviceRegistry的实例，应该是 EurekaServiceRegistry ， 原因是EurekaAutoServiceRegistration的构造方法中，会有一个赋值操作，而这个构造方法是在EurekaClientAutoConfiguration 这个自动装配类中被装配和初始化的，代码如下。
@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);
}
服务的注册
EurekaAutoServiceRegistration.start
public class EurekaAutoServiceRegistration implements AutoServiceRegistration, SmartLifecycle, Ordered, SmartApplicationListener {
@Override
public void start() {
// only set the port if the nonSecurePort or securePort is 0 and this.port != 0
if (this.port.get() != 0) {
if (this.registration.getNonSecurePort() == 0) {
this.registration.setNonSecurePort(this.port.get());
}
if (this.registration.getSecurePort() == 0 && this.registration.isSecure()) {
this.registration.setSecurePort(this.port.get());
}
}
if (!this.running.get() && this.registration.getNonSecurePort() > 0) {
this.serviceRegistry.register(this.registration);
this.context.publishEvent(new InstanceRegisteredEvent<>(this, this.registration.getInstanceConfig()));
this.running.set(true);
}
}
}
this.serviceRegistry.register(this.registration); 方法最终会调用 EurekaServiceRegistry 类中的 register 方法来实现服务注册
EurekaServiceRegistry.register
@Override
public void register(EurekaRegistration reg) {
maybeInitializeClient(reg);
if (log.isInfoEnabled()) {
log.info("Registering application "
+ reg.getApplicationInfoManager().getInfo().getAppName()
+ " with eureka with status "
+ reg.getInstanceConfig().getInitialStatus());
}
//设置当前实例的状态，一旦这个实例的状态发生变化，只要状态不是DOWN，那么就会被监听器监听并且执行服务注册。
reg.getApplicationInfoManager().setInstanceStatus(reg.getInstanceConfig().getInitialStatus());
//设置健康检查的处理
reg.getHealthCheckHandler().ifAvailable(healthCheckHandler -> reg.getEurekaClient().registerHealthCheck(healthCheckHandler));
}
从上述代码来看，注册方法中并没有真正调用Eureka的方法去执行注册，而是仅仅设置了一个状态以及设置健康检查处理器。继续看reg.getApplicationInfoManager().setInstanceStatus方法
public synchronized void setInstanceStatus(InstanceStatus status) {
InstanceStatus next = instanceStatusMapper.map(status);
if (next == null) {
return;
}
InstanceStatus prev = instanceInfo.setStatus(next);
if (prev != null) {
for (StatusChangeListener listener : listeners.values()) {
try {
listener.notify(new StatusChangeEvent(prev, next));
} catch (Exception e) {
logger.warn("failed to notify listener: {}", listener.getId(), e);
}
}
}
}
在这个方法中，它会通过监听器来发布一个状态变更事件。那么此时listener的实例是StatusChangeListener ，也就是调用 StatusChangeListener 的notify方法。这个事件是触发一个服务状态变更，应该是有地方会监听这个事件，然后基于这个事件。
这个时候以为找到了方向，然后进去看，发现它是一个接口。而且我们发现它是静态的内部接口，还无法直接看到它的实现类。
猜测一定是在某个地方做了初始化的工作，于是，找到EurekaServiceRegistry.register方法中的 reg.getApplicationInfoManager 这个实例是什么，而且我们发现ApplicationInfoManager是来自于EurekaRegistration这个类中的属性。而
EurekaRegistration又是在EurekaAutoServiceRegistration这个类中实例化的。那么，是不是在自动装配中做了什么东西。于是找到EurekaClientAutoConfiguration这个类，果然看到了Bean的一些自动装配，其中包含 EurekaClient 、ApplicationInfoMangager 、 EurekaRegistration 等。
EurekaClientConfiguration
@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();
}
}
不难发现，在这里看到了一个很重要的Bean在启动的时候做了自动装配，也就是CloudEurekaClient 。从名字上来看，可以很容易的识别并猜测出它是Eureka客户端的一个工具类，用来实现和服务端的通信以及处理。这个很多源码一贯的套路，要么在构造方法里面去做很多的初始化和一些后台执行的程序操作，要么就是通过异步事件的方式来处理。接着，我们看一下CloudEurekaClient的初始化过程，它的构造方法中会通过 super 调用父类的构造方法。也就是DiscoveryClient的构造。
CloudEurekaClient
super(applicationInfoManager, config, args);调用父类的构造方法，而CloudEurekaClient的父类是DiscoveryClient.
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
我们可以看到在最终的DiscoveryClient改造方法中，有非常长的代码。其实很多代码可以不需要关心，大部分都是一些初始化工作，比如初始化了几个定时任务
- scheduler
- heartbeatExecutor 心跳定时任务
- cacheRefreshExecutor 定时去同步服务端的实例列表
@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
Provider<BackupRegistry> backupRegistryProvider, EndpointRandomizer endpointRandomizer) {
//...
//是否要从eureka server上获取服务地址信息
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;
}
//是否要注册到eureka server上
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());
//如果不需要注册并且不需要更新服务地址
if (!config.shouldRegisterWithEureka() && !config.shouldFetchRegistry()) {
//...
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());
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
//...
//如果需要注册到Eureka server并且是开启了初始化的时候强制注册，则调用register()发起服务注册
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
initScheduledTasks();
try {
Monitors.registerObject(this);
} catch (Throwable e) {
logger.warn("Cannot register timers", e);
}
initTimestampMs = System.currentTimeMillis();
logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}",
initTimestampMs, this.getApplications().size());
}
DiscoveryClient.initScheduledTasks
initScheduledTasks 去启动一个定时任务。如果配置了开启从注册中心刷新服务列表，则会开启cacheRefreshExecutor这个定时任务如果开启了服务注册到Eureka，则通过需要做几个事情.
- 建立心跳检测机制
- 通过内部类来实例化StatusChangeListener 实例状态监控接口，这个就是前面在分析启动过程中所看到的，调用notify的方法，实际上会在这里体现.
private void initScheduledTasks() {
//如果配置了开启从注册中心刷新服务列表，则会开启cacheRefreshExecutor这个定时任务
if (clientConfig.shouldFetchRegistry()) {
// registry cache refresh timer
int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
cacheRefreshTask = new TimedSupervisorTask(
"cacheRefresh",
scheduler,
cacheRefreshExecutor,
registryFetchIntervalSeconds,
TimeUnit.SECONDS,
expBackOffBound,
new CacheRefreshThread()
);
scheduler.schedule(
cacheRefreshTask,
registryFetchIntervalSeconds, TimeUnit.SECONDS);
}
//如果开启了服务注册到Eureka，则通过需要做几个事情
if (clientConfig.shouldRegisterWithEureka()) {
int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
logger.info("Starting heartbeat executor: " + "renew interval is: {}", renewalIntervalInSecs);
// Heartbeat timer
heartbeatTask = new TimedSupervisorTask(
"heartbeat",
scheduler,
heartbeatExecutor,
renewalIntervalInSecs,
TimeUnit.SECONDS,
expBackOffBound,
new HeartbeatThread()
);
scheduler.schedule(
heartbeatTask,
renewalIntervalInSecs, TimeUnit.SECONDS);
// InstanceInfo replicator 初始化一个:instanceInfoReplicator
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();
}
};
//注册实例状态变化的监听
if (clientConfig.shouldOnDemandUpdateStatusChange()) {
applicationInfoManager.registerStatusChangeListener(statusChangeListener);
}
//启动一个实例信息复制器，主要就是为了开启一个定时线程，每40秒判断实例信息是否变更，如果变更了则重新注册
instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
} else {
logger.info("Not registering with Eureka server per configuration");
}
}
instanceInfoReplicator.onDemandUpdate()
这个方法的主要作用是根据实例数据是否发生变化，来触发服务注册中心的数据。
public boolean onDemandUpdate() {
//限流判断(令牌桶算法)
if (rateLimiter.acquire(burstSize, allowedRatePerMinute)) {
if (!scheduler.isShutdown()) {
//提交一个任务
scheduler.submit(new Runnable() {
@Override
public void run() {
logger.debug("Executing on-demand update of local InstanceInfo");
//取出之前已经提交的任务，也就是在start方法中提交的更新任务，如果任务还没有执行完成，则取消之前的任务。
Future latestPeriodic = scheduledPeriodicRef.get();
if (latestPeriodic != null && !latestPeriodic.isDone()) {
logger.debug("Canceling the latest scheduled update, it will be rescheduled at the end of on demand update");
//取出之前已经提交的任务，也就是在start方法中提交的更新任务，如果任务还没有执行完成，则取消之前的任务。
latestPeriodic.cancel(false);
}
//通过调用run方法，令任务在延时后执行，相当于周期性任务中的一次
InstanceInfoReplicator.this.run();
}
});
return true;
} else {
logger.warn("Ignoring onDemand update due to stopped scheduler");
return false;
}
} else {
logger.warn("Ignoring onDemand update due to rate limiter");
return false;
}
}
InstanceInfoReplicator.this.run();
run方法实际上和前面自动装配所执行的服务注册方法是一样的，也就是调用 register 方法进行服务注册，并且在finally中，每30s会定时执行一下当前的run 方法进行检查
public void run() {
try {
discoveryClient.refreshInstanceInfo();
Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
if (dirtyTimestamp != null) {
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);
}
}
DiscoveryClient.register
终于找到服务注册的入口了， eurekaTransport.registrationClient.register 最终调用的是 AbstractJerseyEurekaHttpClient#register(...)`， 这里使用了很多的设计模式，比如工厂模式、装饰器模式等。
boolean register() throws Throwable {
logger.info(PREFIX + "{}: registering service...", appPathIdentifier);
EurekaHttpResponse<Void> httpResponse;
try {
httpResponse = eurekaTransport.registrationClient.register(instanceInfo);
} catch (Exception e) {
logger.warn(PREFIX + "{} - registration failed {}", appPathIdentifier, e.getMessage(), e);
throw e;
}
if (logger.isInfoEnabled()) {
logger.info(PREFIX + "{} - registration status: {}", appPathIdentifier, httpResponse.getStatusCode());
}
return httpResponse.getStatusCode() == Status.NO_CONTENT.getStatusCode();
}
AbstractJerseyEurekaHttpClient#register
很显然，这里是发起了一次http请求，访问Eureka-Server的apps/${APP_NAME}接口，将当前服务实例的信息发送到Eureka Server进行保存。
至此，我们基本上已经知道Spring Cloud Eureka 是如何在启动的时候把服务信息注册到Eureka Server上的了
@Override
public EurekaHttpResponse<Void> register(InstanceInfo info) {
String urlPath = "apps/" + info.getAppName();
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);
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();
}
}
}
但是，似乎最开始的问题还没有解决，也就是Spring Boot应用在启动时，会调用start方法，最终调用StatusChangeListener.notify 去更新服务的一个状态，并没有直接调用register方法注册。所以继续去看 statusChangeListener.notify 方法。
服务总结
至此，我们知道Eureka Client发起服务注册时，有两个地方会执行服务注册的任务
1. 在Spring Boot启动时，由于自动装配机制将CloudEurekaClient注入到了容器，并且执行了构造方法，而在构造方法中有一个定时任务每40s会执行一次判断，判断实例信息是否发生了变化，如果是则会发起服务注册的流程
2. 在Spring Boot启动时，通过refresh方法，最终调用StatusChangeListener.notify进行服务状态变更的监听，而这个监听的方法受到事件之后会去执行服务注册。
