深入Eureka Server启动源码分析（一）

start包配置

spring-cloud-netflix-eureka-server包结构

在这个包下面META-INF下面有个spring.factories这个配置文件

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

使用了springboot EnableAutoConfiguration这个注解，在springboot应用启动的时候，会自动加载EurekaServerAutoConfiguration这个bean，后面主要看这个bean的源码

启动源码分析

EurekaServerAutoConfiguration

用于EurekaServer往beanfactory添加相关eureka-server功能bean

@Configuration
@Import(EurekaServerInitializerConfiguration.class)
@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)
@EnableConfigurationProperties({ EurekaDashboardProperties.class,
      InstanceRegistryProperties.class })
@PropertySource("classpath:/eureka/server.properties")
public class EurekaServerAutoConfiguration extends WebMvcConfigurerAdapter {

    // 此处省略大部分代码，仅抽取一些关键的代码片段

    // 加载EurekaController, spring-cloud 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);
    }
    // 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，需要通知给那些服务节点， （互为一个集群）
    @Bean
    @ConditionalOnMissingBean
    public PeerEurekaNodes peerEurekaNodes(PeerAwareInstanceRegistry registry,
        ServerCodecs serverCodecs) {
        return new PeerEurekaNodes(registry, this.eurekaServerConfig,
         this.eurekaClientConfig, serverCodecs, this.applicationInfoManager);
    }
    // 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);
    }
    // 这个类的作用是spring-cloud和原生eureka的胶水代码，通过这个类来启动EurekaSever
    // 后面这个类会在EurekaServerInitializerConfiguration被调用，进行eureka启动
    @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;
}

// 拦截器实例
@Bean
public javax.ws.rs.core.Application jerseyApplication(Environment environment,
      ResourceLoader resourceLoader) {

   ClassPathScanningCandidateComponentProvider provider = new ClassPathScanningCandidateComponentProvider(
         false, environment);

   // Filter to include only classes that have a particular annotation.
   //
   provider.addIncludeFilter(new AnnotationTypeFilter(Path.class));
   provider.addIncludeFilter(new AnnotationTypeFilter(Provider.class));

   // Find classes in Eureka packages (or subpackages)
   //
   Set<Class<?>> classes = new HashSet<Class<?>>();
   for (String basePackage : EUREKA_PACKAGES) {
      Set<BeanDefinition> beans = provider.findCandidateComponents(basePackage);
      for (BeanDefinition bd : beans) {
         Class<?> cls = ClassUtils.resolveClassName(bd.getBeanClassName(),
               resourceLoader.getClassLoader());
         classes.add(cls);
      }
   }

   // Construct the Jersey ResourceConfig
   //
   Map<String, Object> propsAndFeatures = new HashMap<String, Object>();
   propsAndFeatures.put(
         // Skip static content used by the webapp
         ServletContainer.PROPERTY_WEB_PAGE_CONTENT_REGEX,
         EurekaConstants.DEFAULT_PREFIX + "/(fonts|images|css|js)/.*");

   DefaultResourceConfig rc = new DefaultResourceConfig(classes);
   rc.setPropertiesAndFeatures(propsAndFeatures);

   return rc;
}
}

1.@Configuration 表明这是一个配置类
2.@Import(EurekaServerInitializerConfiguration.class) 导入启动EurekaServer的bean
3.@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class) 这个是表示只有在spring容器里面含有Market这个实例的时候，才会加载当前这个Bean（EurekaServerAutoConfiguration ），这个就是控制是否开启EurekaServer的关键，在@EableEurekaServer这个注解里面，就是创建了一个Market兑现，用来告诉他，我开启了Eureka服务

4.@EnableConfigurationProperties({ EurekaDashboardProperties.class, InstanceRegistryProperties.class })

5.@PropertySource("classpath:/eureka/server.properties") 加载配置文件。

EurekaServerInitializerConfiguration

从上面的代码分析上可以看到，在EurekaServerAutoConfiguration加载完成之后就会执行

EurekaServerInitializerConfiguration这个类的start方法， 这个类实现了spring的SmartLifecyl,后续会开个单章介绍这个类

/**
 * @author Dave Syer
 */
@Configuration
@CommonsLog
public class EurekaServerInitializerConfiguration
      implements ServletContextAware, SmartLifecycle, Ordered {

   @Autowired
   private EurekaServerConfig eurekaServerConfig;

   private ServletContext servletContext;

   @Autowired
   private ApplicationContext applicationContext;

   @Autowired
   private EurekaServerBootstrap eurekaServerBootstrap;

   private boolean running;

   private int order = 1;

   @Override
   public void setServletContext(ServletContext servletContext) {
      this.servletContext = servletContext;
   }

   @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();
   }

   private EurekaServerConfig getEurekaServerConfig() {
      return this.eurekaServerConfig;
   }

   private void publish(ApplicationEvent event) {
      this.applicationContext.publishEvent(event);
   }

   @Override
   public void stop() {
      this.running = false;
      eurekaServerBootstrap.contextDestroyed(this.servletContext);
   }

   @Override
   public boolean isRunning() {
      return this.running;
   }

   @Override
   public int getPhase() {
      return 0;
   }

   @Override
   public boolean isAutoStartup() {
      return true;
   }

   @Override
   public void stop(Runnable callback) {
      callback.run();
   }

   @Override
   public int getOrder() {
      return this.order;
   }

}

EurekaServerBootstrap

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...");
}
PeerAwareInstanceRegistryImpl

@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;
    // 每分钟最小续约数
    this.numberOfRenewsPerMinThreshold =
            (int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());
    logger.info("Got " + count + " instances from neighboring DS node");
    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");
    // 设置实例的状态为UP
    applicationInfoManager.setInstanceStatus(InstanceStatus.UP);
    // 开启定时任务，默认60秒执行一次，用于清理60秒之内没有续约的实例
    super.postInit();
}

PeerEurekaNodes

从上面的EurekaServerAutoConfiguration类，我们可以看到有个初始化EurekaServerContext的方法

@Bean
public EurekaServerContext eurekaServerContext(ServerCodecs serverCodecs,
      PeerAwareInstanceRegistry registry, PeerEurekaNodes peerEurekaNodes) {
   return new DefaultEurekaServerContext(this.eurekaServerConfig, serverCodecs,
         registry, peerEurekaNodes, this.applicationInfoManager);
}

DefaultEurekaServerContext 这个类里面的的initialize()方法是被@PostConstruct 这个注解修饰的,在应用加载的时候，会执行这个方法

public void initialize() throws Exception {
    logger.info("Initializing ...");
    // 启动一个线程，读取其他集群节点的信息，后面后续复制
    peerEurekaNodes.start();
    //
    registry.init(peerEurekaNodes);
    logger.info("Initialized");
}

peerEurekaNodes.start()主要是启动一个只拥有一个线程的线程池，第一次进去会更新一下集群其他节点信息
然后启动了一个定时线程，每60秒更新一次，也就是说后续可以根据配置动态的修改节点配置。（原生的spring cloud config支持）

PeerEurekaNodes

public void start() {
    taskExecutor = Executors.newSingleThreadScheduledExecutor(
            new ThreadFactory() {
                @Override
                public Thread newThread(Runnable r) {
                    Thread thread = new Thread(r, "Eureka-PeerNodesUpdater");
                    thread.setDaemon(true);
                    return thread;
                }
            }
    );
    try {
        // 首次进来，更新集群节点信息
        updatePeerEurekaNodes(resolvePeerUrls());
        // 搞个线程
        Runnable peersUpdateTask = new Runnable() {
            @Override
            public void run() {
                try {
                    updatePeerEurekaNodes(resolvePeerUrls());
                } catch (Throwable e) {
                    logger.error("Cannot update the replica Nodes", e);
                }

            }
        };
        taskExecutor.scheduleWithFixedDelay(
                peersUpdateTask,
                serverConfig.getPeerEurekaNodesUpdateIntervalMs(),
                serverConfig.getPeerEurekaNodesUpdateIntervalMs(),
                TimeUnit.MILLISECONDS
        );
    } catch (Exception e) {
        throw new IllegalStateException(e);
    }
    for (PeerEurekaNode node : peerEurekaNodes) {
        logger.info("Replica node URL:  " + node.getServiceUrl());
    }
}
// 根据URL 构建PeerEurekaNode信息
protected PeerEurekaNode createPeerEurekaNode(String peerEurekaNodeUrl) {
    HttpReplicationClient replicationClient = JerseyReplicationClient.createReplicationClient(serverConfig, serverCodecs, peerEurekaNodeUrl);
    String targetHost = hostFromUrl(peerEurekaNodeUrl);
    if (targetHost == null) {
        targetHost = "host";
    }
    return new PeerEurekaNode(registry, targetHost, peerEurekaNodeUrl, replicationClient, serverConfig);
}

registry.init(peerEurekaNodes);这里面使用的是PeerAwareInstanceRegistryImpl ， 注册信息管理类里面的init方法

1. 构建一个非空的ResponseCache
2. 启动一个定时器，更新eureka的阈值 ，默认每15分钟执行一次 ， 这个阈值主要是用来判断是否开启自我保护机制 , 后面会单独开篇幅来讲解

@Override
public void init(PeerEurekaNodes peerEurekaNodes) throws Exception {
    this.numberOfReplicationsLastMin.start();
    this.peerEurekaNodes = peerEurekaNodes;
    initializedResponseCache();
    scheduleRenewalThresholdUpdateTask();
    initRemoteRegionRegistry();

    try {
        Monitors.registerObject(this);
    } catch (Throwable e) {
        logger.warn("Cannot register the JMX monitor for the InstanceRegistry :", e);
    }
}

至此，EurekaServer算是启动完毕 ， EurekaServerBootstrap是完全复制了原生EurekaBootstrap的代码， 因为原生的Eureka是在servlet应用，但是spring-cloud的应用是运行在内嵌的Tomcat等WEB服务器里面的，这里就是使用EurekaServerBootstrap来做替换，最终是Eureka能够在springboot中使用。