Must be called when the agent is starting

async def _init_clean(self):
        """ Must be called when the agent is starting """
        # Data about running containers
        self._containers_running = {}
        self._container_for_job = {}

        self._student_containers_running = {}
        self._student_containers_for_job = {}

        self._containers_killed = dict()

        # Delete tmp_dir, and recreate-it again
        try:
            await self._ashutil.rmtree(self._tmp_dir)
        except OSError:
            pass

        try:
            await self._aos.mkdir(self._tmp_dir)
        except OSError:
            pass

        # Docker
        self._docker = AsyncProxy(DockerInterface())

        # Auto discover containers
        self._logger.info("Discovering containers")
        self._containers = await self._docker.get_containers()

        self._assigned_external_ports = {}  # container_id : [external_ports]

        if self._address_host is None and len(self._containers) != 0:
            self._logger.info("Guessing external host IP")
            self._address_host = await self._docker.get_host_ip(next(iter(self._containers.values()))["id"])
        if self._address_host is None:
            self._logger.warning(
                "Cannot find external host IP. Please indicate it in the configuration. Remote SSH debug has been deactivated.")
            self._external_ports = None
        else:
            self._logger.info("External address for SSH remote debug is %s", self._address_host)

        # Watchers
        self._timeout_watcher = TimeoutWatcher(self._docker)