apollo-adminservice/src/main/java/com/ctrip/framework/apollo/adminservice/controller/ClusterController.java/ClusterController/isAppIdUnique
class ClusterController:  @GetMapping("/apps/{appId}/cluster/{clusterName}/unique")
  public boolean isAppIdUnique(@PathVariable("appId") String appId,
                               @PathVariable("clusterName") String clusterName) {
    return clusterService.isClusterNameUnique(appId, clusterName);
  }