ansible nspawn connection plugin

I have been playing with system images using ansible and chroots, and I figured that using systemd-nspawn to handle the chroots would make things nice, giving ansible commands the benefit of a running system.

There has been an attempt which was rejected.

Here is my attempt. It does boot the machine then run commands inside it, and it works nicely. The only thing I missed is a way of shutting down the machine at the end, since ansible seems to call close() at the end of each command, and I do not know enough ansible internals to do this right.

I hope this can serve as inspiration for something that works well.

# Based on (c) 2013, Maykel Moya <>
# Based on (c) 2015, Toshio Kuratomi <>
# (c) 2018, Enrico Zini <>
# This is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# Ansible is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with Ansible.  If not, see <>.
from __future__ import (absolute_import, division, print_function)
__metaclass__ = type

import distutils.spawn
import os
import os.path
import pipes
import subprocess
import time
import hashlib

from ansible import constants as C
from ansible.errors import AnsibleError
from ansible.plugins.connection import ConnectionBase, BUFSIZE
from ansible.module_utils.basic import is_executable

    from __main__ import display
except ImportError:
    from ansible.utils.display import Display
    display = Display()

class Connection(ConnectionBase):
    ''' Local chroot based connections '''

    transport = 'schroot'
    has_pipelining = True
    # su currently has an undiagnosed issue with calculating the file
    # checksums (so copy, for instance, doesn't work right)
    # Have to look into that before re-enabling this
    become_methods = frozenset(C.BECOME_METHODS).difference(('su',))

    def __init__(self, play_context, new_stdin, *args, **kwargs):
        super(Connection, self).__init__(play_context, new_stdin, *args, **kwargs)

        self.chroot = self._play_context.remote_addr
        # We need short and fast rather than secure
        m = hashlib.sha1()
        self.machine_name = "ansible-" + m.hexdigest()

        if os.geteuid() != 0:
            raise AnsibleError("nspawn connection requires running as root")

        # we're running as root on the local system so do some
        # trivial checks for ensuring 'host' is actually a chroot'able dir
        if not os.path.isdir(self.chroot):
            raise AnsibleError("%s is not a directory" % self.chroot)

        chrootsh = os.path.join(self.chroot, 'bin/sh')
        # Want to check for a usable bourne shell inside the chroot.
        # is_executable() == True is sufficient.  For symlinks it
        # gets really complicated really fast.  So we punt on finding that
        # out.  As long as it's a symlink we assume that it will work
        if not (is_executable(chrootsh) or (os.path.lexists(chrootsh) and os.path.islink(chrootsh))):
            raise AnsibleError("%s does not look like a chrootable dir (/bin/sh missing)" % self.chroot)

        self.nspawn_cmd = distutils.spawn.find_executable('systemd-nspawn')
        if not self.nspawn_cmd:
            raise AnsibleError("systemd-nspawn command not found in PATH")
        self.machinectl_cmd = distutils.spawn.find_executable('machinectl')
        if not self.machinectl_cmd:
            raise AnsibleError("machinectl command not found in PATH")
        self.run_cmd = distutils.spawn.find_executable('systemd-run')
        if not self.run_cmd:
            raise AnsibleError("systemd-run command not found in PATH")

        existing =[self.machinectl_cmd, "show", self.machine_name], stdout=open("/dev/null", "wb"))
        self.machine_exists = existing == 0

    def set_host_overrides(self, host, hostvars=None):
        super(Connection, self).set_host_overrides(host, hostvars)

    def _connect(self):
        ''' connect to the chroot; nothing to do here '''
        super(Connection, self)._connect()
        if not self._connected:
            if not self.machine_exists:
                display.vvv("Starting nspawn machine", host=self.chroot)
                self.chroot_proc = subprocess.Popen([self.nspawn_cmd, "-D", self.chroot, "-M", self.machine_name, "--register=yes", "--boot"], stdout=open("/dev/null", "w"))
                self.chroot_proc = None
                display.vvv("Reusing nspawn machine", host=self.chroot)
            self._connected = True

    def _local_run_cmd(self, cmd, stdin=None):
        display.vvv(" -exec %s" % repr(cmd), host=self.chroot)
        display.vvv(" -  or %s" % " ".join(pipes.quote(x) for x in cmd), host=self.chroot)
        p = subprocess.Popen(cmd, shell=False, stdin=subprocess.PIPE,
                             stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        stdout, stderr = p.communicate(stdin)
        display.vvv(" - got %d" % p.returncode, host=self.chroot)
        display.vvv(" - out %s" % repr(stdout), host=self.chroot)
        display.vvv(" - err %s" % repr(stderr), host=self.chroot)
        return p.returncode, stdout, stderr

    def _systemd_run_cmd(self, cmd, stdin=None):
        local_cmd = [self.run_cmd, "-M", self.machine_name, "-q", "--pipe", "--wait", "-E", "HOME=/root", "-E", "USER=root", "-E", "LOGNAME=root"] + cmd
        local_cmd = [x.encode("utf8") if isinstance(x, unicode) else x for x in local_cmd]
        return self._local_run_cmd(local_cmd, stdin=stdin)

    def exec_command(self, cmd, in_data=None, sudoable=False):
        ''' run a command on the chroot '''
        super(Connection, self).exec_command(cmd, in_data=in_data, sudoable=sudoable)

        display.vvv("cmd: %s" % repr(cmd), host=self.chroot)
        return self._systemd_run_cmd(["/bin/sh", "-c", cmd], stdin=in_data)

    def _prefix_login_path(self, remote_path):
        ''' Make sure that we put files into a standard path

            If a path is relative, then we need to choose where to put it.
            ssh chooses $HOME but we aren't guaranteed that a home dir will
            exist in any given chroot.  So for now we're choosing "/" instead.
            This also happens to be the former default.

            Can revisit using $HOME instead if it's a problem
        if not remote_path.startswith(os.path.sep):
            remote_path = os.path.join(os.path.sep, remote_path)
        return os.path.normpath(remote_path)

    def put_file(self, in_path, out_path):
        ''' transfer a file from local to chroot '''
        super(Connection, self).put_file(in_path, out_path)
        display.vvv("PUT %s TO %s" % (in_path, out_path), host=self.chroot)

        out_path = pipes.quote(self._prefix_login_path(out_path))
        p = subprocess.Popen([self.machinectl_cmd, "-q", "copy-to", self.machine_name, in_path, out_path], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        stdout, stderr = p.communicate()
        if p.returncode != 0:
            raise AnsibleError("failed to transfer file %s to %s:\n%s\n%s" % (in_path, out_path, stdout, stderr))

    def fetch_file(self, in_path, out_path):
        ''' fetch a file from chroot to local '''
        super(Connection, self).fetch_file(in_path, out_path)
        display.vvv("FETCH %s TO %s" % (in_path, out_path), host=self.chroot)

        in_path = pipes.quote(self._prefix_login_path(in_path))
        p = subprocess.Popen([self.machinectl_cmd, "-q", "copy-from", self.machine_name, in_path, out_path], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        stdout, stderr = p.communicate()
        if p.returncode != 0:
            raise AnsibleError("failed to transfer file %s from %s:\n%s\n%s" % (out_path, in_path, stdout, stderr))

    def close(self):
        super(Connection, self).close()

# FIXME: how can we power off the machine? close and __del__ seem to be called after each command
#    def __del__(self):
#        ''' terminate the connection; nothing to do here '''
#        # super(Connection, self).close()
#        display.vvv("CLOSE", host=self.chroot)
#        if self._connected:
#            p, stdout, stderr = self._local_run_cmd([self.machinectl_cmd, "poweroff", self.machine_name])
#            if p == 0 and self.chroot_proc:
#                self.chroot_proc.wait()
#            self._connected = False