Eureka 源码分析之 Eureka Server

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地址 : https://mp.weixin.qq.com/s/FfJrAGQuHyVrsedtbr0Ihw

简介

上一篇文章《Eureka 源码分析之 Eureka Client》 通过源码知道 ，eureka Client 是通过 http rest来 与 eureka server 交互，实现 注册服务，续约服务，服务下线 等。本篇探究下eureka server。

源码分析

从 @EnableEurekaServer 注解为入口分析，通过源码可以看出他是一个标记注解：

/**
 * Annotation to activate Eureka Server related configuration {@link 
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(EurekaServerMarkerConfiguration.class)
public @interface EnableEurekaServer {

}

从注释可以知道，用来激活 eureka server 的 配置类 EurekaServerAutoConfiguration 中相关配置，EurekaServerAutoConfiguration 的关键代码如下：

@Configuration
@Import(EurekaServerInitializerConfiguration.class)
@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)
@EnableConfigurationProperties({ EurekaDashboardProperties.class,
		InstanceRegistryProperties.class })
@PropertySource("classpath:/eureka/server.properties")
public class EurekaServerAutoConfiguration extends WebMvcConfigurerAdapter {
	/**
	 * List of packages containing Jersey resources required by the Eureka server
	 */
	private static final String[] EUREKA_PACKAGES = new String[] { "com.netflix.discovery",
			"com.netflix.eureka" };

	@Autowired
	private ApplicationInfoManager applicationInfoManager;

	@Autowired
	private EurekaServerConfig eurekaServerConfig;

	@Autowired
	private EurekaClientConfig eurekaClientConfig;

	@Autowired
	private EurekaClient eurekaClient;

	@Autowired
	private InstanceRegistryProperties instanceRegistryProperties;

	public static final CloudJacksonJson JACKSON_JSON = new CloudJacksonJson();

	@Bean
	public HasFeatures eurekaServerFeature() {
		return HasFeatures.namedFeature("Eureka Server",
				EurekaServerAutoConfiguration.class);
	}

	@Configuration
	protected static class EurekaServerConfigBeanConfiguration {
		// 创建并加载EurekaServerConfig的实现类，主要是Eureka-server的配置信息
		@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;
		}
	}

	//加载EurekaController，SpringCloud 提供了一些额外的接口，用来获取eurekaServer的信息
	@Bean
	@ConditionalOnProperty(prefix = "eureka.dashboard", name = "enabled", matchIfMissing = true)
	public EurekaController eurekaController() {
		return new EurekaController(this.applicationInfoManager);
	}

	//省略 ...
	
	// 接收客户端的注册等请求就是通过InstanceRegistry来处理的，是真正处理业务的类，接下来会详细分析
	@Bean
	public PeerAwareInstanceRegistry peerAwareInstanceRegistry(
			ServerCodecs serverCodecs) {
		this.eurekaClient.getApplications(); // force initialization
		return new InstanceRegistry(this.eurekaServerConfig, this.eurekaClientConfig,
				serverCodecs, this.eurekaClient,
				this.instanceRegistryProperties.getExpectedNumberOfRenewsPerMin(),
				this.instanceRegistryProperties.getDefaultOpenForTrafficCount());
	}
	
	//配置服务节点信息，这里的作用主要是为了配置Eureka的peer节点，也就是说当有收到有节点注册上来的时候，需要通知给哪些节点
	@Bean
	@ConditionalOnMissingBean
	public PeerEurekaNodes peerEurekaNodes(PeerAwareInstanceRegistry registry,
			ServerCodecs serverCodecs) {
		return new RefreshablePeerEurekaNodes(registry, this.eurekaServerConfig,
				this.eurekaClientConfig, serverCodecs, this.applicationInfoManager);
	}
	
	//省略 ...	
	
	//EurekaServer的上下文
	@Bean
	public EurekaServerContext eurekaServerContext(ServerCodecs serverCodecs,
			PeerAwareInstanceRegistry registry, PeerEurekaNodes peerEurekaNodes) {
		return new DefaultEurekaServerContext(this.eurekaServerConfig, serverCodecs,
				registry, peerEurekaNodes, this.applicationInfoManager);
	}
	
	// 初始化Eureka-server，会同步其他注册中心的数据到当前注册中心
	@Bean
	public EurekaServerBootstrap eurekaServerBootstrap(PeerAwareInstanceRegistry registry,
			EurekaServerContext serverContext) {
		return new EurekaServerBootstrap(this.applicationInfoManager,
				this.eurekaClientConfig, this.eurekaServerConfig, registry,
				serverContext);
	}

	// 配置拦截器，ServletContainer里面实现了jersey框架，通过他来实现eurekaServer对外的restFull接口
	@Bean
	public FilterRegistrationBean jerseyFilterRegistration(
			javax.ws.rs.core.Application eurekaJerseyApp) {
		FilterRegistrationBean bean = new FilterRegistrationBean();
		bean.setFilter(new ServletContainer(eurekaJerseyApp));
		bean.setOrder(Ordered.LOWEST_PRECEDENCE);
		bean.setUrlPatterns(
				Collections.singletonList(EurekaConstants.DEFAULT_PREFIX + "/*"));

		return bean;
	}

	//省略 ...
	

}

从EurekaServerAutoConfiguration 类上的注解@Import(EurekaServerInitializerConfiguration.class) 可以到，实例化类EurekaServerAutoConfiguration之前，已经实例化了EurekaServerInitializerConfiguration类，代码如下：

@Configuration
@CommonsLog
public class EurekaServerInitializerConfiguration
      implements ServletContextAware, SmartLifecycle, Ordered {
 
   // 此处省略部分代码
 
   @Override
   public void start() {
      // 启动一个线程
      new Thread(new Runnable() {
         @Override
         public void run() {
            try {
               //初始化EurekaServer，同时启动Eureka Server ，后面着重讲这里
               eurekaServerBootstrap.contextInitialized(EurekaServerInitializerConfiguration.this.servletContext);
               log.info("Started Eureka Server");
                // 发布EurekaServer的注册事件
               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，后面会讲到。
               publish(new EurekaServerStartedEvent(getEurekaServerConfig()));
            }
            catch (Exception ex) {
               // Help!
               log.error("Could not initialize Eureka servlet context", ex);
            }
         }
      }).start();
   }
 
   // 此处省略部分代码
 
}

这个start方法中开启了一个新的线程，然后进行一些Eureka Server的初始化工作，比如调用eurekaServerBootstrap的contextInitialized方法，EurekaServerBootstrap代码如下：

public class EurekaServerBootstrap {

	// 此处省略部分代码

	public void contextInitialized(ServletContext context) {
	   try {
	      // 初始化Eureka的环境变量
	      initEurekaEnvironment();
	      // 初始化Eureka的上下文
	      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 initEurekaEnvironment() throws Exception {
	   log.info("Setting the eureka configuration..");
	 
	   String dataCenter = ConfigurationManager.getConfigInstance()
	         .getString(EUREKA_DATACENTER);
	   if (dataCenter == null) {
	      log.info(
	            "Eureka data center value eureka.datacenter is not set, defaulting to default");
	      ConfigurationManager.getConfigInstance()
	            .setProperty(ARCHAIUS_DEPLOYMENT_DATACENTER, DEFAULT);
	   }
	   else {
	      ConfigurationManager.getConfigInstance()
	            .setProperty(ARCHAIUS_DEPLOYMENT_DATACENTER, dataCenter);
	   }
	   String environment = ConfigurationManager.getConfigInstance()
	         .getString(EUREKA_ENVIRONMENT);
	   if (environment == null) {
	      ConfigurationManager.getConfigInstance()
	            .setProperty(ARCHAIUS_DEPLOYMENT_ENVIRONMENT, TEST);
	      log.info(
	            "Eureka environment value eureka.environment is not set, defaulting to test");
	   }
	   else {
	      ConfigurationManager.getConfigInstance()
	            .setProperty(ARCHAIUS_DEPLOYMENT_ENVIRONMENT, environment);
	   }
	}
	 
	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
	   this.registry.openForTraffic(this.applicationInfoManager, registryCount);
	 
	   // Register all monitoring statistics.
	   EurekaMonitors.registerAllStats();
	}
	public void contextDestroyed(ServletContext context) {
	   try {
	      log.info("Shutting down Eureka Server..");
	      context.removeAttribute(EurekaServerContext.class.getName());
	 
	      destroyEurekaServerContext();
	      destroyEurekaEnvironment();
	 
	   }
	   catch (Throwable e) {
	      log.error("Error shutting down eureka", e);
	   }
	   log.info("Eureka Service is now shutdown...");
	}
	
}

在初始化Eureka Server上下文环境后，就会继续执行openForTraffic方法，这个方法主要是设置了期望每分钟接收到的心跳次数，并将服务实例的状态设置为UP，最后又通过方法postInit来开启一个定时任务，用于每隔一段时间（默认60秒）将没有续约的服务实例（默认90秒没有续约）清理掉。openForTraffic的方法代码如下：

@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.expectedNumberOfRenewsPerMin = count * 2;
    // 计算每分钟最小续约数
    this.numberOfRenewsPerMinThreshold =
            (int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());
    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();
    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");
    // 修改服务实例的状态为UP
    applicationInfoManager.setInstanceStatus(InstanceStatus.UP);
    // 开启定时任务，每隔一段时间（默认60秒）将没有续约的服务实例（默认90秒没有续约）清理掉
    super.postInit();
}

postInit方法开启了一个新的定时任务，代码如下：

protected void postInit() {
    renewsLastMin.start();
    if (evictionTaskRef.get() != null) {
        evictionTaskRef.get().cancel();
    }
    evictionTaskRef.set(new EvictionTask());
    evictionTimer.schedule(evictionTaskRef.get(),
            serverConfig.getEvictionIntervalTimerInMs(),
            serverConfig.getEvictionIntervalTimerInMs());
}

这里的时间间隔都来自于EurekaServerConfigBean类，可以在配置文件中以eureka.server开头的配置来进行设置。

参考

https://www.e-learn.cn/content/qita/775244/
https://nobodyiam.com/2016/06/25/dive-into-eureka/
https://blog.csdn.net/Lammonpeter/article/details/84330900

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