Eureka客户端源码-本地注册表更新

下载注册表有两种情况：全量下载和增量下载

private boolean fetchRegistry(boolean forceFullRegistryFetch) {
  try {
    //第一次获取注册表，applications为空或者已经注册到Eureka中的应用size为0
    //禁用增量更新、强制全量获取、本地注册表数
    //或者配置了vipAddress
    Applications applications = getApplications();
    if (clientConfig.shouldDisableDelta()
        || (!Strings.isNullOrEmpty(clientConfig.getRegistryRefreshSingleVipAddress()))
        || forceFullRegistryFetch
        || (applications == null)
        || (applications.getRegisteredApplications().size() == 0)
        || (applications.getVersion() == -1)) //Client application does not have latest library supporting delta
    {
      //全量下载
      getAndStoreFullRegistry();
    } else {
      //增量更新
      getAndUpdateDelta(applications);
    }
  }
  // Notify about cache refresh before updating the instance remote status
  onCacheRefreshed();
  // Update remote status based on refreshed data held in the cache
  updateInstanceRemoteStatus();
  // registry was fetched successfully, so return true
  return true;
}

1. 全量下载

   全量下载相对来说比较简单

   private void getAndStoreFullRegistry() throws Throwable {
     Applications apps = null;
     EurekaHttpResponse httpResponse = 
       clientConfig.getRegistryRefreshSingleVipAddress() == null
       ? eurekaTransport.queryClient.getApplications(remoteRegionsRef.get())
       : eurekaTransport.queryClient.getVip(clientConfig.getRegistryRefreshSingleVipAddress(), remoteRegionsRef.get());
     if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
       //从EurekaServer获取所有的注册信息
       apps = httpResponse.getEntity();
     }
     if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
       //添加到本地缓存中（把返回的数据顺序进行打算处理，以及过滤掉状态是非在线的服务保留在线服务
       //(通过config中的shouldFilterOnlyUpInstances进行配置为 true)）
       localRegionApps.set(this.filterAndShuffle(apps));
     }
   }
   

2. 增量下载

   private void getAndUpdateDelta(Applications applications) throws Throwable {
     Applications delta = null;
     //获取增量注册表信息
     EurekaHttpResponse httpResponse = eurekaTransport.queryClient.
     getDelta(remoteRegionsRef.get());
     if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
       delta = httpResponse.getEntity();
     }
     //如果增量请求数据为空，则进行全量下载
     if (delta == null) {
       getAndStoreFullRegistry();
     } else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
       String reconcileHashCode = "";
       if (fetchRegistryUpdateLock.tryLock()) {
         try {
           //更新本地注册表
           updateDelta(delta);
           //获取注册表的hashcode信息，感兴趣的可以在跟进去看看具体的实现逻辑
           reconcileHashCode = getReconcileHashCode(applications);
         } finally {
           fetchRegistryUpdateLock.unlock();
         }
       } 
       // There is a diff in number of instances for some reason
       // 如果delta获取的的instance数据量和本地注册表的数量不一致 则进行全量下载
       if (!reconcileHashCode.equals(delta.getAppsHashCode()) || clientConfig.shouldLogDeltaDiff()) {
         reconcileAndLogDifference(delta, reconcileHashCode);  // this makes a remoteCall
       }
     }
   }
   

   private void updateDelta(Applications delta) {
     int deltaCount = 0;
     for (Application app : delta.getRegisteredApplications()) {
       for (InstanceInfo instance : app.getInstances()) {
         //本地注册表信息
         Applications applications = getApplications();
         //获取实例的region
         String instanceRegion = instanceRegionChecker.getInstanceRegion(instance);
         //判断是否是本地region
         if (!instanceRegionChecker.isLocalRegion(instanceRegion)) {
           Applications remoteApps = remoteRegionVsApps.get(instanceRegion);
           if (null == remoteApps) {
             remoteApps = new Applications();
             remoteRegionVsApps.put(instanceRegion, remoteApps);
           }
           //如果是非localRegion则把远程Apps赋值给applications
           applications = remoteApps;
         }
         ++deltaCount;
         if (ActionType.ADDED.equals(instance.getActionType())) {
           //从本地注册表中获取Application
           Application existingApp = applications.getRegisteredApplications(instance.getAppName());
           //如果不存在，则把增量更新到的这个app添加到applications中
           if (existingApp == null) {
             //把application添加到注册表中
             applications.addApplication(app);
           }
           //然后把app的实例信息添加到实例列表里面
           //看下面addInstance的注释
           applications.getRegisteredApplications(instance.getAppName()).addInstance(instance);
         } else if (ActionType.MODIFIED.equals(instance.getActionType())) {
           Application existingApp = applications.getRegisteredApplications(instance.getAppName());
           if (existingApp == null) {
             applications.addApplication(app);
           }
           applications.getRegisteredApplications(instance.getAppName()).addInstance(instance);
         } else if (ActionType.DELETED.equals(instance.getActionType())) {
           Application existingApp = applications.getRegisteredApplications(instance.getAppName());
           if (existingApp != null) {
             //从本地注册表中移除实例
             existingApp.removeInstance(instance);
             //如果本地注册表中该应用下面没有实例信息了，则移除该应用
             if (existingApp.getInstancesAsIsFromEureka().isEmpty()) {
               applications.removeApplication(existingApp);
             }
           }
         }
       }
     }
   }
   

   public void addInstance(InstanceInfo i) {
     instancesMap.put(i.getId(), i);
     synchronized (instances) {
       //instances 是set类型的,并且instanceInfo重写equals方法，
       //在更新的时候 如果instanceId不变，不进行移除是不会覆盖的，
       //所以先进行remove然后在进行add
       instances.remove(i);
       instances.add(i);
       isDirty = true;
     }
   }
   

总结：

1. 全量下载时机或者条件
   • 第一次获取注册表
   • 禁用增量下载
   • 配置了VIPaddress
   • 增量更新没有获取数据时，进行全量下载
   • 增量数据和本地注册表数据的hashcode(或者说instance数量不一致)则进行全量下载