Eureka源码解析服务离线状态变更

环境

• eureka版本：1.10.11
• Spring Cloud : 2020.0.2
• Spring Boot ：2.4.4
  测试代码：github.com/hsfxuebao/s…

1. 服务离线的方式

服务离线，即某服务不能对外提供服务了。服务离线的原因有两种：服务下架与服务下线。

• 服务下架：表示这个已经被kill掉了，不能对外提供服务，自己也不能访问
• 服务下线：只是该服务不能被 eureka server端发现（不能注册），不能被远程访问，但是可以自己访问自己的服务

1.1 基于Actuator监控器实现

提交如下POST请求，可实现相应的服务离线操作：

• 服务下架：http://localhost:端口号/actuator/shutdown 无需请求体
• 服务下线：http://localhost:端口号/actuator/serviceregistry 请求体为（该方法称为服务平滑上下 线）

{
    "status":"OUT_OF_SERVICE"  或 "UP"
}

注意，从Spring Cloud 2020.0.0版本开始，服务平滑上下线的监控终端由service-registry变更为 了serviceregistry

1.2 直接向Eureka Server提交请求

可以通过直接向Eureka Server提交不同的请求的方式来实现指定服务离线操作:

服务下架：通过向eureka server发送DELETE请求来删除指定client的服务

http://${server}:${port}/eureka/apps/${serviceName}/${instanceId}

服务下线：通过向eureka server发送PUT请求来修改指定client的status，其中${value}的取值 为：OUT_OF_SERVICE或UP

http://${server}:${port}/eureka/apps/${serviceName}/${instanceId}/stat us?value=${value}

1.3 特殊状态CANCEL_OVERRIDE

用户提交的状态修改请求中指定的状态，除了InstanceInfo的内置枚举类InstanceStatus中定义的状态 外，还可以是CANCEL_OVERRIDE状态。

若用户提交的状态为CANCEL_OVERRIDE，则Client会通过Jersey向Server提交一个DELETE请求，用于 在Server端将对应InstanceInfo的overridenStatus修改为UNKNWON，即删除了原来的overridenStatus 的状态值。此时，该Client发送的心跳Server是不接收的。Server会向该Client返回404。

2. 服务下架源码

public class EurekaClientAutoConfiguration {
   @Configuration(proxyBeanMethods = false)
   @ConditionalOnRefreshScope
   protected static class RefreshableEurekaClientConfiguration {
      @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, @Autowired(required = false) HealthCheckHandler healthCheckHandler) {
      }
  }
}

当Actuator监听到服务下架时，会调用DiscoveryClient.shutdown()方法：

// 服务下架
@PreDestroy
@Override
public synchronized void shutdown() {
    if (isShutdown.compareAndSet(false, true)) {
        logger.info("Shutting down DiscoveryClient ...");
        // 注销状态改变监听器
        if (statusChangeListener != null && applicationInfoManager != null) {
            applicationInfoManager.unregisterStatusChangeListener(statusChangeListener.getId());
        }
        // todo 取消定时任务
        cancelScheduledTasks();
        // If APPINFO was registered
        if (applicationInfoManager != null
                && clientConfig.shouldRegisterWithEureka()
                && clientConfig.shouldUnregisterOnShutdown()) {
            applicationInfoManager.setInstanceStatus(InstanceStatus.DOWN);
            // todo 服务下架
            unregister();
        }
        if (eurekaTransport != null) {
            eurekaTransport.shutdown();
        }
        heartbeatStalenessMonitor.shutdown();
        registryStalenessMonitor.shutdown();
        Monitors.unregisterObject(this);
        logger.info("Completed shut down of DiscoveryClient");
    }
}

有两个核心方法，我们分别看一下。

2.1 cancelScheduledTasks()

取消定时任务。

private void cancelScheduledTasks() {
    if (instanceInfoReplicator != null) {
        instanceInfoReplicator.stop();
    }
    if (heartbeatExecutor != null) {
        heartbeatExecutor.shutdownNow();
    }
    if (cacheRefreshExecutor != null) {
        cacheRefreshExecutor.shutdownNow();
    }
    if (scheduler != null) {
        scheduler.shutdownNow();
    }
    if (cacheRefreshTask != null) {
        cacheRefreshTask.cancel();
    }
    if (heartbeatTask != null) {
        heartbeatTask.cancel();
    }
}

2.2 unregister()

发送服务下架请求。

void unregister() {
    // It can be null if shouldRegisterWithEureka == false
    if(eurekaTransport != null && eurekaTransport.registrationClient != null) {
        try {
            logger.info("Unregistering ...");
            EurekaHttpResponse<Void> httpResponse = eurekaTransport.registrationClient.cancel(instanceInfo.getAppName(), instanceInfo.getId());
            logger.info(PREFIX + "{} - deregister  status: {}", appPathIdentifier, httpResponse.getStatusCode());
        } catch (Exception e) {
            logger.error(PREFIX + "{} - de-registration failed{}", appPathIdentifier, e.getMessage(), e);
        }
    }
}

@Override
public EurekaHttpResponse<Void> cancel(String appName, String id) {
    String urlPath = "apps/" + appName + '/' + id;
    ClientResponse response = null;
    try {
        Builder resourceBuilder = jerseyClient.resource(serviceUrl).path(urlPath).getRequestBuilder();
        addExtraHeaders(resourceBuilder);
        // delete 请求
        response = resourceBuilder.delete(ClientResponse.class);
        return anEurekaHttpResponse(response.getStatus()).headers(headersOf(response)).build();
    } finally {
        if (logger.isDebugEnabled()) {
            logger.debug("Jersey HTTP DELETE {}/{}; statusCode={}", serviceUrl, urlPath, response == null ? "N/A" : response.getStatus());
        }
        if (response != null) {
            response.close();
        }
    }
}

服务下架请求：DELETE请求，path："apps/" + appName + '/' + id;

3. 服务下线源码分析（状态变更）

Eureka 整合了 Actuator ，可以通过 Actuator 变更实例在服务端的状态。spring cloud整合eureka，入口在 spring-cloud-common下的spring.factories:

@Configuration(proxyBeanMethods = false)
public class ServiceRegistryAutoConfiguration {
   @ConditionalOnBean(ServiceRegistry.class)
   @ConditionalOnClass(Endpoint.class)
   protected class ServiceRegistryEndpointConfiguration {
      @Autowired(required = false)
      private Registration registration;
      @Bean
      @ConditionalOnAvailableEndpoint
      public ServiceRegistryEndpoint serviceRegistryEndpoint(ServiceRegistry serviceRegistry) {
         ServiceRegistryEndpoint endpoint = new ServiceRegistryEndpoint(serviceRegistry);
         endpoint.setRegistration(this.registration);
         return endpoint;
      }
   }
}

ServiceRegistryAutoConfiguration是一个配置类，往容器中注入ServiceRegistryEndpoint：

@Endpoint(id = "serviceregistry")
public class ServiceRegistryEndpoint {
    ...
   @WriteOperation
   public ResponseEntity<?> setStatus(String status) {
      Assert.notNull(status, "status may not by null");
      if (this.registration == null) {
         return ResponseEntity.status(HttpStatus.NOT_FOUND).body("no registration found");
      }
      // 变更状态
      this.serviceRegistry.setStatus(this.registration, status);
      return ResponseEntity.ok().build();
   }
   @ReadOperation
   public ResponseEntity getStatus() {
      if (this.registration == null) {
         return ResponseEntity.status(HttpStatus.NOT_FOUND).body("no registration found");
      }
       // 获取状态
      return ResponseEntity.ok().body(this.serviceRegistry.getStatus(this.registration));
   }
}

3.1 变更状态

核心方法ServiceRegistry#setStatus:

@Override
public void setStatus(EurekaRegistration registration, String status) {
   // 获取实例信息
   InstanceInfo info = registration.getApplicationInfoManager().getInfo();
   // TODO: howto deal with delete properly?
   if ("CANCEL_OVERRIDE".equalsIgnoreCase(status)) {
      // 如果变更状态请求传过来 status = "CANCEL_OVERRIDE"，向服务端发起 Jersey 删除状态请求
      registration.getEurekaClient().cancelOverrideStatus(info);
      return;
   }
   // TODO: howto deal with status types across discovery systems?
   InstanceInfo.InstanceStatus newStatus = InstanceInfo.InstanceStatus.toEnum(status);
   // 如果不是删除状态，则向服务端发起 Jersey 变更状态请求
   registration.getEurekaClient().setStatus(newStatus, info);
}

核心流程有2个，分别为

status为CANCEL_OVERRIDE:

public void cancelOverrideStatus(InstanceInfo info) {
   getEurekaHttpClient().deleteStatusOverride(info.getAppName(), info.getId(), info);
}
@Override
public EurekaHttpResponse<Void> deleteStatusOverride(String appName, String id, InstanceInfo info) {
    String urlPath = "apps/" + appName + '/' + id + "/status";
    ClientResponse response = null;
    try {
        Builder requestBuilder = jerseyClient.resource(serviceUrl)
                .path(urlPath)
                .queryParam("lastDirtyTimestamp", info.getLastDirtyTimestamp().toString())
                .getRequestBuilder();
        addExtraHeaders(requestBuilder);
        // DELETE 请求
        response = requestBuilder.delete(ClientResponse.class);
        return anEurekaHttpResponse(response.getStatus()).headers(headersOf(response)).build();
    } finally {
        if (logger.isDebugEnabled()) {
            logger.debug("Jersey HTTP DELETE {}/{}; statusCode={}", serviceUrl, urlPath, response == null ? "N/A" : response.getStatus());
        }
        if (response != null) {
            response.close();
        }
    }
}

删除deleteStatusOverride请求: DELETE请求 path："apps/" + appName + '/' + id + "/status"

直接调用setStatus()方法：

@Override
public EurekaHttpResponse<Void> statusUpdate(String appName, String id, InstanceStatus newStatus, InstanceInfo info) {
    String urlPath = "apps/" + appName + '/' + id + "/status";
    ClientResponse response = null;
    try {
        Builder requestBuilder = jerseyClient.resource(serviceUrl)
                .path(urlPath)
                .queryParam("value", newStatus.name())
                .queryParam("lastDirtyTimestamp", info.getLastDirtyTimestamp().toString())
                .getRequestBuilder();
        addExtraHeaders(requestBuilder);
        // PUT 请求
        response = requestBuilder.put(ClientResponse.class);
        return anEurekaHttpResponse(response.getStatus()).headers(headersOf(response)).build();
    } finally {
        if (logger.isDebugEnabled()) {
            logger.debug("Jersey HTTP PUT {}/{}; statusCode={}", serviceUrl, urlPath, response == null ? "N/A" : response.getStatus());
        }
        if (response != null) {
            response.close();
        }
    }
}

变更状态请求：PUT请求，path为 ："apps/" + appName + '/' + id + "/status"

3.2 获取状态

// EurekaServiceRegistry.class
public Object getStatus(EurekaRegistration registration) {
    String appname = registration.getApplicationInfoManager().getInfo().getAppName();
    String instanceId = registration.getApplicationInfoManager().getInfo().getId();
    // 获取本地实例信息
    InstanceInfo info = registration.getEurekaClient().getInstanceInfo(appname,
	    instanceId);
    HashMap<String, Object> status = new HashMap<>();
    if (info != null) {
        // 从实例信息取出相应状态返回
	status.put("status", info.getStatus().toString());
	status.put("overriddenStatus", info.getOverriddenStatus().toString());
    }
    else {
        // 如果实例信息不存在，则返回 UNKNOWN 状态
	status.put("status", UNKNOWN.toString());
    }
    return status;
}

参考文章

eureka-0.10.11源码（注释）

springcloud-source-study学习github地址

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