def docker_container_ids(broker):
        """Command: docker_container_ids"""
        containers = broker[DefaultSpecs.docker_list_containers]
        try:
            result = set()
            for l in containers.content[1:]:
                result.add(l.split(None)[3].strip())
        except:
            raise ContentException("No docker containers.")
        if result:
            return list(result)
        raise ContentException("No docker containers.")
Command: docker_container_ids