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Eureka 源码分析之 Eureka Server

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。