def update_app_blb_rs(self, blb_id, sg_id,
                          backend_server_list,
                          client_token=None,
                          config=None):
        """
        update backend server for the specified LoadBalancer and server group,
        support batch update

        :param blb_id:
                id of LoadBalancer
        :type blb_id:string

        :param sg_id:
            id of the server group
        :type sg_id:string

        :param backend_server_list
                List of backend servers to be added
        https://cloud.baidu.com/doc/BLB/API.html#AppBackendServer
        :type backend_server_list:List<AppBackendServer>

        :param client_token:
            If the clientToken is not specified by the user, a random String
            generated by default algorithm will be used.
        :type client_token: string

        :param config:
        :type config: baidubce.BceClientConfiguration

        :return:
        :rtype baidubce.bce_response.BceResponse
        """
        path = utils.append_uri(self.version, 'appblb', blb_id, 'blbrs')
        params = {}

        if client_token is None:
            params[b'clientToken'] = generate_client_token()
        else:
            params[b'clientToken'] = client_token

        body = {
            'sgId': compat.convert_to_string(sg_id),
            'backendServerList': backend_server_list
        }

        return self._send_request(http_methods.PUT, path,
                                  body=json.dumps(body), params=params,
                                  config=config)