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Spring Cloud Eureka服务续约(Renew)源码分析

xujin · 6年前 · 3013 ·

Renew(服务续约)

概述

Renew（服务续约）操作由Service Provider定期调用，类似于heartbeat。目的是隔一段时间Service Provider调用接口，告诉Eureka Server它还活着没挂，不要把它T了。通俗的说就是它们两之间的心跳检测，避免服务提供者被剔除掉。
请参考:Spring Cloud Eureka名词解释
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服务续约配置

Renew操作会在Service Provider定时发起，用来通知Eureka Server自己还活着。 这里有两个比较重要的配置需要如下，可以在Run之前配置。

  eureka.instance.leaseRenewalIntervalInSeconds

Renew频率。默认是30秒，也就是每30秒会向Eureka Server发起Renew操作。

  eureka.instance.leaseExpirationDurationInSeconds

服务失效时间。默认是90秒，也就是如果Eureka Server在90秒内没有接收到来自Service Provider的Renew操作，就会把Service Provider剔除。

Renew源码分析

服务提供者实现细节

服务提供者发发起服务续约的时序图，如下图所示,大家先直观的看一下时序图，等阅读完源码再回顾一下。
服务提供者发起续约时序图

  1. 在com.netflix.discovery.DiscoveryClient.initScheduledTasks()中的1272行，TimedSupervisorTask会定时发起服务续约，代码如下所示:

    // Heartbeat timer
scheduler.schedule(
   new TimedSupervisorTask(
          "heartbeat",
           scheduler,
           heartbeatExecutor,
           renewalIntervalInSecs,
           TimeUnit.SECONDS,
           expBackOffBound,
            new HeartbeatThread()
          ),
renewalIntervalInSecs, TimeUnit.SECONDS);

    2.在com.netflix.discovery.DiscoveryClient中的1393行，有一个HeartbeatThread线程发起续约操作

    private class HeartbeatThread implements Runnable {

     public void run() {
         //调用eureka-client中的renew
         if (renew()) {
             lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis();
         }
     }
}

    renew()调用eureka-client-1.4.11.jarcom.netflix.discovery.DiscoveryClient中829行renew()发起PUT Reset请求，调用com.netflix.eureka.resources.InstanceResource中的renewLease()续约。

    /**
  * Renew with the eureka service by making the appropriate REST call
  */
 boolean renew() {
     EurekaHttpResponse<InstanceInfo> httpResponse;
     try {
         httpResponse = eurekaTransport.registrationClient.sendHeartBeat(instanceInfo.getAppName(), instanceInfo.getId(), instanceInfo, null);
         logger.debug("{} - Heartbeat status: {}", PREFIX + appPathIdentifier, httpResponse.getStatusCode());
         if (httpResponse.getStatusCode() == 404) {
             REREGISTER_COUNTER.increment();
             logger.info("{} - Re-registering apps/{}", PREFIX + appPathIdentifier, instanceInfo.getAppName());
             return register();
         }
         return httpResponse.getStatusCode() == 200;
     } catch (Throwable e) {
         logger.error("{} - was unable to send heartbeat!", PREFIX + appPathIdentifier, e);
         return false;
     }
}

    Netflix中的Eureka Core实现细节

    NetFlix中Eureka Core中的服务续约时序图，如下图所示。
    服务续约时序图

    1. 打开com.netflix.eureka.resources.InstanceResource中的106行的renewLease()方法，代码如下:
      ```java
      private final PeerAwareInstanceRegistry registry
      @PUT
      public Response renewLease(
        @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication,
  @QueryParam("overriddenstatus") String overriddenStatus,
  @QueryParam("status") String status,
  @QueryParam("lastDirtyTimestamp") String lastDirtyTimestamp) {
      boolean isFromReplicaNode = “true”.equals(isReplication);
      //调用
      boolean isSuccess = registry.renew(app.getName(), id, isFromReplicaNode);
      //其余省略
      }
 2. 点开registry.renew(app.getName(), id, isFromReplicaNode);我们可以看到，调用了`org.springframework.cloud.netflix.eureka.server.InstanceRegistry`中的`renew（）`方法，代码如下:
```java
    @Override
    public boolean renew(final String appName, final String serverId,
            boolean isReplication) {
        log("renew " + appName + " serverId " + serverId + ", isReplication {}"
                + isReplication);
        List<Application> applications = getSortedApplications();
        for (Application input : applications) {
            if (input.getName().equals(appName)) {
                InstanceInfo instance = null;
                for (InstanceInfo info : input.getInstances()) {
                    if (info.getHostName().equals(serverId)) {
                        instance = info;
                        break;
                    }
                }
                publishEvent(new EurekaInstanceRenewedEvent(this, appName, serverId,
                        instance, isReplication));
                break;
            }
        }
        //调用com.netflix.eureka.registry.PeerAwareInstanceRegistryImpl中的renew方法
        return super.renew(appName, serverId, isReplication);
}

3.从super.renew()看到调用了父类中的com.netflix.eureka.registry.PeerAwareInstanceRegistryImpl中420行的renew()方法，代码如下:

 public boolean renew(final String appName, final String id, final boolean isReplication) {
        //服务续约成功，
        if (super.renew(appName, id, isReplication)) {
            //然后replicateToPeers同步其它Eureka Server中的数据
            replicateToPeers(Action.Heartbeat, appName, id, null, null, isReplication);
            return true;
        }
        return false;
}

3.1 从上面代码中super.renew(appName, id, isReplication)可以看出调用的是com.netflix.eureka.registry.AbstractInstanceRegistry中345行的renew()方法，代码如下所示

  public boolean renew(String appName, String id, boolean isReplication) {
        RENEW.increment(isReplication);
        Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
        Lease<InstanceInfo> leaseToRenew = null;
        if (gMap != null) {
            leaseToRenew = gMap.get(id);
        }
        if (leaseToRenew == null) {
            RENEW_NOT_FOUND.increment(isReplication);
            logger.warn("DS: Registry: lease doesn't exist, registering resource: {} - {}", appName, id);
            return false;
        } else {
            InstanceInfo instanceInfo = leaseToRenew.getHolder();
            if (instanceInfo != null) {
                // touchASGCache(instanceInfo.getASGName());
                InstanceStatus overriddenInstanceStatus = this.getOverriddenInstanceStatus(
                        instanceInfo, leaseToRenew, isReplication);
                if (overriddenInstanceStatus == InstanceStatus.UNKNOWN) {
                    logger.info("Instance status UNKNOWN possibly due to deleted override for instance {}"
                            + "; re-register required", instanceInfo.getId());
                    RENEW_NOT_FOUND.increment(isReplication);
                    return false;
                }
                if (!instanceInfo.getStatus().equals(overriddenInstanceStatus)) {
                    Object[] args = {
                            instanceInfo.getStatus().name(),
                            instanceInfo.getOverriddenStatus().name(),
                            instanceInfo.getId()
                    };
                    logger.info(
                            "The instance status {} is different from overridden instance status {} for instance {}. "
                                    + "Hence setting the status to overridden status", args);
                    instanceInfo.setStatus(overriddenInstanceStatus);
                }
            }
            renewsLastMin.increment();
            leaseToRenew.renew();
            return true;
        }
    }

其中 leaseToRenew.renew()是调用com.netflix.eureka.lease.Lease<T>中的62行的renew()方法

    /**
     * Renew the lease, use renewal duration if it was specified by the
     * associated {@link T} during registration, otherwise default duration is
     * {@link #DEFAULT_DURATION_IN_SECS}.
     */
    public void renew() {
        lastUpdateTimestamp = System.currentTimeMillis() + duration;

    }

3.2 replicateToPeers(Action.Heartbeat, appName, id, null, null, isReplication);调用自身的replicateToPeers()方法，在com.netflix.eureka.registry.PeerAwareInstanceRegistryImpl中的618行，主要接口实现方式和register基本一致：首先更新自身Eureka Server中服务的状态，再同步到其它Eureka Server中。

private void replicateToPeers(Action action, String appName, String id,
                                  InstanceInfo info /* optional */,
                                  InstanceStatus newStatus /* optional */, boolean isReplication) {
        Stopwatch tracer = action.getTimer().start();
        try {
            if (isReplication) {
                numberOfReplicationsLastMin.increment();
            }
            // If it is a replication already, do not replicate again as this will create a poison replication
            if (peerEurekaNodes == Collections.EMPTY_LIST || isReplication) {
                return;
            }
            // 同步把续约信息同步到其它的Eureka Server中
            for (final PeerEurekaNode node : peerEurekaNodes.getPeerEurekaNodes()) {
                // If the url represents this host, do not replicate to yourself.
                if (peerEurekaNodes.isThisMyUrl(node.getServiceUrl())) {
                    continue;
                }
                //根据action做相应操作的同步
                replicateInstanceActionsToPeers(action, appName, id, info, newStatus, node);
            }
        } finally {
            tracer.stop();
        }
 }

至此，Eureka服务续约源码分析结束，大家有兴趣可自行阅读。

源码分析链接

其它源码分析链接:
Spring Cloud中@EnableEurekaClient源码分析:
http://xujin.org/sc/sc-enableEurekaClient-annonation/
Spring Cloud Eureka服务注册源码分析：
http://xujin.org/sc/sc-eureka-register/

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