def describe_rs_mount(self, blb_id, sg_id, config=None):
        """
        describe servers of specific server group

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

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

        :param config:
        :type config: baidubce.BceClientConfiguration

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

        params = {
            'sgId': compat.convert_to_string(sg_id)
        }

        return self._send_request(http_methods.GET, path, params=params,
                                  config=config)