Eureka Eureka Server source code analysis of the

No. article first appeared in public, "the programmer fruit"
Address: https://mp.weixin.qq.com/s/FfJrAGQuHyVrsedtbr0Ihw

Brief introduction

An article on "Eureka source code analysis of the Eureka Client" by source know, eureka Client by http rest eureka server to interact with the implementation of the registration services, renewal services, and other services offline. Benpian inquiry under eureka server.

Source code analysis

From the annotated inlet @EnableEurekaServer analysis through source code you can see that he is a comment tag:

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

}

Be understood from the comment, configured to activate the class EurekaServerAutoConfiguration eureka server configuration, the key code EurekaServerAutoConfiguration follows:

@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 ...
    

}

Annotations from @Import (EurekaServerInitializerConfiguration.class) on EurekaServerAutoConfiguration to class, instantiating class EurekaServerAutoConfiguration before, the EurekaServerInitializerConfiguration instantiated class code is as follows:

@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
 
}

The start method opens up a new thread, and then some initialization Eureka Server, such as call contextInitialized method of eurekaServerBootstrap, EurekaServerBootstrap code is as follows:

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...");
    }
    
}

After initialization Eureka Server context, we will continue openForTraffic method, which is mainly to set the expectations of beats per minute received, and the state of the service instance for the UP, and finally to open a timed task by means of postInit for (default 60 seconds) the service instances did not renew from time to time (default 90 seconds did not renew) cleared away. openForTraffic method code is as follows:

@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 opened a new method of timing tasks, as follows:

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

Here are the time interval from EurekaServerConfigBean classes, may be arranged at the beginning of eureka.server disposed in the configuration file.

reference

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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