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SpringCloud Eureka 服务注册实现过程

作者:巡山小妖N

这篇文章主要介绍了SpringCloud Eureka 服务注册实现过程,文中通过示例代码介绍的非常详细,对大家的学习或者工作具有一定的参考学习价值,需要的朋友可以参考下

一、将服务注册到Eureka

一个SpringBoot应用如果要注册到Spring Cloud环境(Greenwich.SR3版本),步骤很简单:

pom.xml中添加启动器:spring-cloud-starter-netflix-eureka-client;

增加配置:eureka.client.serviceUrl.defaultZone: http://localhost:8100/eureka/;

启动应用;

如果注册中心正常,此时就能在注册中心发现这个应用了,如下图红框所示:

按照spring.factories中的配置,EurekaClientAutoConfiguration中的配置都会生效,包括下面这段代码返回的bean:

@Bean
public DiscoveryClient discoveryClient(EurekaInstanceConfig config, EurekaClient client) {
  return new EurekaDiscoveryClient(config, client);
}

spring容器初始化时会实例化所有单例bean,就会执行EurekaClientAutoConfiguration的discoveryClient方法获取这个bean实例,于是就构造了一个EurekaDiscoveryClient对象;

注意EurekaDiscoveryClient的构造方法,第二个入参是com.netflix.discovery.EurekaClient类型,此对象同样来自EurekaClientAutoConfiguration类,如下方法:

@Bean(destroyMethod = "shutdown")
@ConditionalOnMissingBean(value = EurekaClient.class, search = SearchStrategy.CURRENT)
@org.springframework.cloud.context.config.annotation.RefreshScope
@Lazy
public EurekaClient eurekaClient(ApplicationInfoManager manager, EurekaClientConfig config, EurekaInstanceConfig instance) {
  manager.getInfo(); // force initialization
  return new CloudEurekaClient(manager, config, this.optionalArgs,this.context);
}

CloudEurekaClient的父类com.netflix.discovery.DiscoveryClient来自netflix发布的eureka-client包中,所以可以这么理解:EurekaDiscoveryClient类是个代理身份,真正的服务注册发现是委托给netflix的开源包来完成的,我们可以专心的使用SpringCloud提供的服务注册发现功能,只需要知道EurekaDiscoveryClient即可,真正的服务是eureka-client来完成的;

接下来需要关注com.netflix.discovery.DiscoveryClient的构造方法,因为这里面有服务注册的逻辑,整个构造方法内容太多,无需都细看,只看关键代码即可;

DiscoveryClient的构造方法中,最熟悉的应该是下图红框中这段日志输出的了:

对应的应用启动日志中就有这段日志输出,如下图红框:

红框中的”us-east-1”,是默认的region,来自配置类EurekaClientConfigBean,这里面有各种eureka相关的配置信息,以及默认配置,如下图:

继续看DiscoveryClient的构造方法,服务注册相关的initScheduledTasks方法在此被调用,如下图:

initScheduledTasks方法的内容如下,请注意中文注释:

  private void initScheduledTasks() {
    //获取服务注册列表信息
    if (clientConfig.shouldFetchRegistry()) {
      //服务注册列表更新的周期时间
      int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
      int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
      //定时更新服务注册列表
      scheduler.schedule(
          new TimedSupervisorTask(
              "cacheRefresh",
              scheduler,
              cacheRefreshExecutor,
              registryFetchIntervalSeconds,
              TimeUnit.SECONDS,
              expBackOffBound,
              new CacheRefreshThread() //该线程执行更新的具体逻辑
          ),
          registryFetchIntervalSeconds, TimeUnit.SECONDS);
    }
    if (clientConfig.shouldRegisterWithEureka()) {
      //服务续约的周期时间
      int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
      int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
      //应用启动可见此日志,内容是:Starting heartbeat executor: renew interval is: 30
      logger.info("Starting heartbeat executor: " + "renew interval is: " + renewalIntervalInSecs);
      // 定时续约
      scheduler.schedule(
          new TimedSupervisorTask(
              "heartbeat",
              scheduler,
              heartbeatExecutor,
              renewalIntervalInSecs,
              TimeUnit.SECONDS,
              expBackOffBound,
              new HeartbeatThread() //该线程执行续约的具体逻辑
          ),
          renewalIntervalInSecs, TimeUnit.SECONDS);

      //这个Runable中含有服务注册的逻辑
      instanceInfoReplicator = new InstanceInfoReplicator(
          this,
          instanceInfo,
          clientConfig.getInstanceInfoReplicationIntervalSeconds(),
          2); // burstSize

      statusChangeListener = new ApplicationInfoManager.StatusChangeListener() {
        @Override
        public String getId() {
          return "statusChangeListener";
        }

        @Override
        public void notify(StatusChangeEvent statusChangeEvent) {
          if (InstanceStatus.DOWN == statusChangeEvent.getStatus() ||
              InstanceStatus.DOWN == statusChangeEvent.getPreviousStatus()) {
            // log at warn level if DOWN was involved
            logger.warn("Saw local status change event {}", statusChangeEvent);
          } else {
            logger.info("Saw local status change event {}", statusChangeEvent);
          }
          instanceInfoReplicator.onDemandUpdate();
        }
      };

      if (clientConfig.shouldOnDemandUpdateStatusChange()) {
        applicationInfoManager.registerStatusChangeListener(statusChangeListener);
      }
      //服务注册
      instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
    } else {
      logger.info("Not registering with Eureka server per configuration");
    }
  }

上述代码中有几处需要注意,这些关键点在后面的章节将继续展开:

a. 周期性更新服务列表;

b. 周期性服务续约;

c. 服务注册逻辑被放入Runnable实现类InstanceInfoReplicator之中,在新线程中执行;

以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持脚本之家。

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