def set_backup_heartbeat(self, interface_id):
        """
        Set this interface as the backup heartbeat interface.
        Clusters and Master NGFW Engines only.
        
        :param str,int interface_id: interface as backup
        :raises InterfaceNotFound: specified interface is not found
        :raises UpdateElementFailed: failure to update interface
        :return: None
        """
        self.interface.set_unset(interface_id, 'backup_heartbeat')
        self._engine.update()