apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/service/InstanceService.java/InstanceService/getInstanceCountByNamespace
class InstanceService:  public int getInstanceCountByNamespace(String appId, Env env, String clusterName, String namespaceName){
    return instanceAPI.getInstanceCountByNamespace(appId, env, clusterName, namespaceName);
  }