微服务治理之Eureka--源码浅析

Eureka集群项目介绍

图中表示Eureka集群的整个动作流程。集群内有3个节点、3个应用服务，服务列表使用的是双层Map，第一层key—>服务名，第二层key->实例名，value是实例信息（ip、port、url等）

@EnableEurekaServer 自动配置

第一步：@Bean Marker对象来激活EurekaServerMarkerConfiguration配置类

我们进入到@EnableEurekaServer注解中看看：

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

关键代码在@Import(EurekaServerMarkerConfiguration.class)，来看下源码：

@Configuration(proxyBeanMethods = false)
public class EurekaServerMarkerConfiguration {@Beanpublic Marker eurekaServerMarkerBean() {return new Marker();}class Marker {}
}

此时，spring下下文中就有了Marker的实例

第二步：自动配置EurekaServerConfiguration类

在spring-cloud-netflix-eureka-server/META-INF/spring.factories中配置了一个自动配置的类EurekaServerAutoConfiguration，而想要激活必须要满足条件@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)，也就是必须要有Marker实例，这一个已在上一步完成
配置代码
spring.factories：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration

EurekaServerAutoConfiguration 配置类：

@Configuration(proxyBeanMethods = false)
@Import(EurekaServerInitializerConfiguration.class)
@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)
...
public class EurekaServerAutoConfiguration implements WebMvcConfigurer {

在EurekaServerAutoConfiguration类中都是注册各种Bean，在类上还有一个关键注解@Import(EurekaServerInitializerConfiguration.class)，代码如下：

@Configuration(proxyBeanMethods = false)
public class EurekaServerInitializerConfiguration implements ServletContextAware, SmartLifecycle, Ordered {private static final Log log = LogFactory.getLog(EurekaServerInitializerConfiguration.class);// 服务端配置@Autowiredprivate EurekaServerConfig eurekaServerConfig;private ServletContext servletContext;@Autowiredprivate ApplicationContext applicationContext;@Autowiredprivate EurekaServerBootstrap eurekaServerBootstrap;private boolean running;private int order = 1;@Overridepublic void setServletContext(ServletContext servletContext) {this.servletContext = servletContext;}@Overridepublic void start() {new Thread(() -> {try {// 上下文初始化eurekaServerBootstrap.contextInitialized(EurekaServerInitializerConfiguration.this.servletContext);log.info("Started Eureka Server");publish(new EurekaRegistryAvailableEvent(getEurekaServerConfig()));EurekaServerInitializerConfiguration.this.running = true;publish(new EurekaServerStartedEvent(getEurekaServerConfig()));}catch (Exception ex) {// Help!log.error("Could not initialize Eureka servlet context", ex);}}).start();}// EurekaServer配置private EurekaServerConfig getEurekaServerConfig() {return this.eurekaServerConfig;}private void publish(ApplicationEvent event) {this.applicationContext.publishEvent(event);}@Overridepublic void stop() {this.running = false;eurekaServerBootstrap.contextDestroyed(this.servletContext);}@Overridepublic boolean isRunning() {return this.running;}// 获取阶段@Overridepublic int getPhase() {return 0;}// 是否自动启动，这里为true@Overridepublic boolean isAutoStartup() {return true;}@Overridepublic int getOrder() {return this.order;}}

实现的是一个SmartLifecycle，它又继承Lifecycle接口，主要方法在start()，使用一个线程进行启动EurekaServer

第三步：谁来调用EurekaServerInitializerConfiguration.start()方法？

在spring初始化上下文中，主要的方法在AbstractApplicationContext.refresh()方法来实现各种依赖注入，其中包括生命中周期

public abstract class AbstractApplicationContext extends DefaultResourceLoaderimplements ConfigurableApplicationContext {@Overridepublic void refresh() throws BeansException, IllegalStateException {...finishRefresh();}protected void finishRefresh() {...// 将刷新传播到各个生命周期处理器getLifecycleProcessor().onRefresh();...}
}

LifecycleProcessor是一个接口，默认的实现是DefaultLifecycleProcessor类，实现了OnRefresh()方法

 @Overridepublic void onRefresh() {startBeans(true);this.running = true;}private void startBeans(boolean autoStartupOnly) {Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans();Map<Integer, LifecycleGroup> phases = new TreeMap<>();lifecycleBeans.forEach((beanName, bean) -> {if (!autoStartupOnly || (bean instanceof SmartLifecycle && ((SmartLifecycle) bean).isAutoStartup())) {int phase = getPhase(bean);phases.computeIfAbsent(phase,p -> new LifecycleGroup(phase, this.timeoutPerShutdownPhase, lifecycleBeans, autoStartupOnly)).add(beanName, bean);}});if (!phases.isEmpty()) {phases.values().forEach(LifecycleGroup::start);}}

startBeans()方法大致过程如下：

获取所有实现Lifecycle接口的Bean
筛选实例为SmartLifecycle且isAutoStartup()方法返回true
根据getPhase()方法进行分组保存到TreeMap中，key为phase，value为：LifecycleGroup类
遍历执行map中每个LifecycleGroup对象的start()方法
最终会调用bean.start()方法，也就是EurekaServerInitializerConfiguration.start()

到这里，@EnableEurekaServer基本就完成了它的使命，调用了EurekaServer初始化的代码。

EurekaServer 启动过程

第一步：EurekaServerInitializerConfiguration.start() 方法

 @Overridepublic void start() {new Thread(() -> {try {// note 上下文初始化eurekaServerBootstrap.contextInitialized(EurekaServerInitializerConfiguration.this.servletContext);log.info("Started Eureka Server");// 发送可用事件publish(new EurekaRegistryAvailableEvent(getEurekaServerConfig()));EurekaServerInitializerConfiguration.this.running = true;// 发送启动事件publish(new EurekaServerStartedEvent(getEurekaServerConfig()));}catch (Exception ex) {// Help!log.error("Could not initialize Eureka servlet context", ex);}}).start();}

关键代码是contextInitialized()方法，EurekaServerBootstrap代码如下：

 public void contextInitialized(ServletContext context) {try {initEurekaEnvironment();// note 初始化EurekaServer上下文initEurekaServerContext();context.setAttribute(EurekaServerContext.class.getName(), this.serverContext);}catch (Throwable e) {log.error("Cannot bootstrap eureka server :", e);throw new RuntimeException("Cannot bootstrap eureka server :", e);}}protected void initEurekaServerContext() throws Exception {// For backward compatibilityJsonXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(), XStream.PRIORITY_VERY_HIGH);XmlXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(), XStream.PRIORITY_VERY_HIGH);// 针对AWS的处理逻辑if (isAws(this.applicationInfoManager.getInfo())) {this.awsBinder = new AwsBinderDelegate(this.eurekaServerConfig, this.eurekaClientConfig, this.registry,this.applicationInfoManager);this.awsBinder.start();}EurekaServerContextHolder.initialize(this.serverContext);log.info("Initialized server context");// 从邻近的eureka节点复制注册表int registryCount = this.registry.syncUp();// 服务剔除逻辑this.registry.openForTraffic(this.applicationInfoManager, registryCount);// 注册所有监控统计信息EurekaMonitors.registerAllStats();}

主要就是对邻近节点的服务列表进行备份、服务剔除逻辑、注册所有监控信息操作

第二步：this.registry.syncUp() 同步eureka节点服务列表

 // 从邻近的DS节点复制整个条目public int syncUp() {int count = 0;for (int i = 0; ((i < serverConfig.getRegistrySyncRetries()) && (count == 0)); i++) {if (i > 0) {try {Thread.sleep(serverConfig.getRegistrySyncRetryWaitMs());} catch (InterruptedException e) {logger.warn("Interrupted during registry transfer..");break;}}// 获得所有节点的应用列表数据Applications apps = eurekaClient.getApplications();for (Application app : apps.getRegisteredApplications()) {for (InstanceInfo instance : app.getInstances()) {try {// 如果可以注册则执行注册操作if (isRegisterable(instance)) {register(instance, instance.getLeaseInfo().getDurationInSecs(), true);count++;}} catch (Throwable t) {logger.error("During DS init copy", t);}}}}return count;}

第三步：服务剔除逻辑 this.registry.openForTraffic(this.applicationInfoManager, registryCount);

调用的是PeerAwareInstanceRegistry类：

    public void openForTraffic(ApplicationInfoManager applicationInfoManager, int count) {// 更新每30秒发生一次this.expectedNumberOfClientsSendingRenews = count;// 期望最小每分钟续租次数updateRenewsPerMinThreshold();logger.info("Got {} instances from neighboring DS node", count);logger.info("Renew threshold is: {}", numberOfRenewsPerMinThreshold);this.startupTime = System.currentTimeMillis();if (count > 0) {this.peerInstancesTransferEmptyOnStartup = false;}DataCenterInfo.Name selfName = applicationInfoManager.getInfo().getDataCenterInfo().getName();// 针对AWS的处理逻辑boolean isAws = Name.Amazon == selfName;if (isAws && serverConfig.shouldPrimeAwsReplicaConnections()) {logger.info("Priming AWS connections for all replicas..");primeAwsReplicas(applicationInfoManager);}logger.info("Changing status to UP");// 将EurekaSserver实例状态设置为UPapplicationInfoManager.setInstanceStatus(InstanceStatus.UP);// 开启EvictionTask()的schedule计划任务，默认每60秒执行一次剔除操作super.postInit();}

定时检测服务剔除操作task（EvictionTask）：

public abstract class AbstractInstanceRegistry implements InstanceRegistry {...protected void postInit() {renewsLastMin.start();if (evictionTaskRef.get() != null) {evictionTaskRef.get().cancel();}evictionTaskRef.set(new EvictionTask());// task：剔除检测任务// delay：首次执行delay// period：执行周期，默认60秒，可以配置evictionTimer.schedule(evictionTaskRef.get(),serverConfig.getEvictionIntervalTimerInMs(),serverConfig.getEvictionIntervalTimerInMs());}
}

任务剔除操作EvictionTask代码：

 class EvictionTask extends TimerTask {private final AtomicLong lastExecutionNanosRef = new AtomicLong(0l);@Overridepublic void run() {try {long compensationTimeMs = getCompensationTimeMs();logger.info("Running the evict task with compensationTime {}ms", compensationTimeMs);// 执行服务剔除操作evict(compensationTimeMs);} catch (Throwable e) {logger.error("Could not run the evict task", e);}}...}// 服务剔除public void evict(long additionalLeaseMs) {...// 超期的实例List<Lease<InstanceInfo>> expiredLeases = new ArrayList<>();// 双层Map，第一层key—>服务名，第二层key->实例名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);}}}}int registrySize = (int) getLocalRegistrySize();int registrySizeThreshold = (int) (registrySize * serverConfig.getRenewalPercentThreshold());int evictionLimit = registrySize - registrySizeThreshold;int toEvict = Math.min(expiredLeases.size(), evictionLimit);if (toEvict > 0) {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();// 服务剔除internalCancel(appName, id, false);}}}protected boolean internalCancel(String appName, String id, boolean isReplication) {read.lock();try {// 获取此服务名下所有的实例Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);Lease<InstanceInfo> leaseToCancel = null;if (gMap != null) {// 移除实例leaseToCancel = gMap.remove(id);}...} finally {read.unlock();}...return true;}

至此，Eureka 服务端源码解析完成。

@EnableEurekaClient 自动配置

在EurekaClient中，@EnableEurekaClient注解是可选的，因为默认会被spring boot自动配置扫描并加载
spring-cloud-netflix-eureka-client/META-INF/spring.factories：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.cloud.netflix.eureka.config.EurekaClientConfigServerAutoConfiguration,\
org.springframework.cloud.netflix.eureka.config.DiscoveryClientOptionalArgsConfiguration,\
org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration,\
org.springframework.cloud.netflix.eureka.EurekaDiscoveryClientConfiguration,\
org.springframework.cloud.netflix.eureka.reactive.EurekaReactiveDiscoveryClientConfiguration,\
org.springframework.cloud.netflix.eureka.loadbalancer.LoadBalancerEurekaAutoConfigurationorg.springframework.cloud.bootstrap.BootstrapConfiguration=\
org.springframework.cloud.netflix.eureka.config.EurekaConfigServerBootstrapConfigurationorg.springframework.boot.Bootstrapper=\
org.springframework.cloud.netflix.eureka.config.EurekaConfigServerBootstrapper

配置比服务端多，关键看EurekaClientAutoConfiguration，代码如下：

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties
@ConditionalOnClass(EurekaClientConfig.class)
@ConditionalOnProperty(value = "eureka.client.enabled", matchIfMissing = true)
@ConditionalOnDiscoveryEnabled
@AutoConfigureBefore({ CommonsClientAutoConfiguration.class, ServiceRegistryAutoConfiguration.class })
@AutoConfigureAfter(name = { "org.springframework.cloud.netflix.eureka.config.DiscoveryClientOptionalArgsConfiguration","org.springframework.cloud.autoconfigure.RefreshAutoConfiguration","org.springframework.cloud.netflix.eureka.EurekaDiscoveryClientConfiguration","org.springframework.cloud.client.serviceregistry.AutoServiceRegistrationAutoConfiguration" })
public class EurekaClientAutoConfiguration {...
}

可以看到，如果要自动配置，必须满足三个condition，分别为：

@ConditionalOnClass(EurekaClientConfig.class)：必须要有EurekaClientConfig类
@ConditionalOnProperty(value = “eureka.client.enabled”, matchIfMissing = true)：就是EnableEurekaClient注解，不配置的话默认为true

@ConditionalOnDiscoveryEnabled

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@ConditionalOnProperty(value = {"spring.cloud.discovery.enabled"},matchIfMissing = true
)
public @interface ConditionalOnDiscoveryEnabled {}

默认为true，可以不用配置

所以默认是所有的Condition都满足，会自动启动EurekaClient服务

总结

对Eureka中涉及到的自动配置原理进行解析，并对EurekaServer端的源码浅析，如果要更加深入可以自行查看源码