Eureka源码解析

简介

• 简单使用参考 Eureka服务发现
• 参考：http://www.iocoder.cn/Eureka/

客户端初始化

• 客户端在引入pom依赖后，通过@EnableDiscoveryClient即可开启服务发现功能，因此以此注解为入口进行查看源码 ^1
  • 此类属于spring-cloud-commons-2.0.2.RELEASE.jar包下，为 springcloud 对 netflix-eureka 的封装

• @EnableDiscoveryClient 注解是用来启用 DiscoveryClient 的实现，核心的实现为EurekaDiscoveryClient

  public class EurekaDiscoveryClient implements DiscoveryClient {
      public static final String DESCRIPTION = "Spring Cloud Eureka Discovery Client";
      private final EurekaInstanceConfig config;
      // EurekaDiscoveryClient 只是关联了 com.netflix.discovery.EurekaClient，具体的服务发现还是由 EurekaClient 完成
      private final EurekaClient eurekaClient;
  
      public EurekaDiscoveryClient(EurekaInstanceConfig config, EurekaClient eurekaClient) {
          this.config = config;
          this.eurekaClient = eurekaClient;
      }
      // ...
  }

• EurekaClient 接口类图说明

  

  • CloudEurekaClient 为 springcloud 对 DiscoveryClient 的继承，具体的逻辑还是由 DiscoveryClient 完成
• DiscoveryClient 类说明
  • register() 客户端注册
  • renew() 客户端续约
  • fetchRegistry() 获取注册的服务列表
  • shutdown() 客户端下线

// AbstractDiscoveryClientOptionalArgs 自定义参数，可通过自定义Bean继承此类以到达定制化某些功能
@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args, Provider<BackupRegistry> backupRegistryProvider) {
    // ...
    logger.info("Initializing Eureka in region {}", this.clientConfig.getRegion());
    // 获取配置 eureka.client.register-with-eureka=true(是否注册到eureka)、eureka.client.fetch-registry=true(是否拉取已注册的服务列表)
    if (!config.shouldRegisterWithEureka() && !config.shouldFetchRegistry()) {
        logger.info("Client configured to neither register nor query for data.");
        this.scheduler = null;
        this.heartbeatExecutor = null;
        this.cacheRefreshExecutor = null;
        this.eurekaTransport = null;
        this.instanceRegionChecker = new InstanceRegionChecker(new PropertyBasedAzToRegionMapper(config), this.clientConfig.getRegion());
        DiscoveryManager.getInstance().setDiscoveryClient(this);
        DiscoveryManager.getInstance().setEurekaClientConfig(config);
        this.initTimestampMs = System.currentTimeMillis();
        logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}", this.initTimestampMs, this.getApplications().size());
    } else {
        try {
            // 创建scheduler定时任务的线程池
            this.scheduler = Executors.newScheduledThreadPool(2, (new ThreadFactoryBuilder()).setNameFormat("DiscoveryClient-%d").setDaemon(true).build());
            // 心跳检查线程池(服务续约)
            this.heartbeatExecutor = new ThreadPoolExecutor(1, this.clientConfig.getHeartbeatExecutorThreadPoolSize(), 0L, TimeUnit.SECONDS, new SynchronousQueue(), (new ThreadFactoryBuilder()).setNameFormat("DiscoveryClient-HeartbeatExecutor-%d").setDaemon(true).build());
            // 服务获取
            this.cacheRefreshExecutor = new ThreadPoolExecutor(1, this.clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0L, TimeUnit.SECONDS, new SynchronousQueue(), (new ThreadFactoryBuilder()).setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d").setDaemon(true).build());
            this.eurekaTransport = new DiscoveryClient.EurekaTransport();
            // 初始化 EurekaHttpClient：eurekaTransport.registrationClient 和 eurekaTransport.queryClient。基于 EurekaHttpClientFactory 初始化
            this.scheduleServerEndpointTask(this.eurekaTransport, args);
        }
        // ...

        // 开启上面三个线程池，往上面3个线程池分别添加相应任务
        // 然后创建了一个instanceInfoReplicator(Runnable任务)，然后调用InstanceInfoReplicator.start方法，把这个任务放进上面scheduler定时任务线程池(服务注册并更新)
        this.initScheduledTasks();

        // ...
    }
    // ...
}

• 流程图

  

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参考文章