ansible dynamic inventory script generates inventory based off of running docker containers

dockerinv.py

#!/usr/bin/env python

'''
This file is an ansible dynamic inventory script used to help resolve docker
containers for ansible.

It only considers running docker containers that have the label
'ansible_managed_container=true'. Other labels will become host groups. eg.

(docker-compose)
...
    labels:
      ansible_managed_container: "true"
      role: "webservers"
...

(resulted host group)
...
[label_role_webservers]
....

Do not rename this script as docker.py, as it will conflict with the docker
python library.
'''

# (c) 2017, Jordan Cohen
#
# This file is part of Ansible,
#
# Ansible 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
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# 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 <http://www.gnu.org/licenses/>.

######################################################################


import json
from collections import defaultdict

import docker


def convert_unsafe_chars(val):
    unsafe_chars = ['=', '-', '.']
    rep_char = '_'

    ret_str = val
    for char in unsafe_chars:
        ret_str = ret_str.replace(char, rep_char)

    return ret_str


def docker_inventory():

    # the docker label that identifies a container for ansible management
    docker_label_identifier = 'ansible_managed_container=true'

    # ansible host group prefix for docker labels
    group_prefix = 'label_'

    # default host vars to apply to all docker hosts
    default_host_vars = {'ansible_connection': 'docker'}

    # main
    client = docker.from_env()
    ansible_managed = client.containers.list(
        filters={'label': docker_label_identifier})

    # return dict
    inv = defaultdict(list)

    # group ansible managed docker hosts as docker_hosts and add default vars
    default_tag = group_prefix + convert_unsafe_chars(docker_label_identifier)
    inv['docker_hosts'] = {'vars': default_host_vars,
                           'children': [default_tag]}

    # add all ansible managed docker hosts to the inventory
    for container in ansible_managed:
        for k, v in container.attrs['Config']['Labels'].iteritems():
            key = convert_unsafe_chars('%s%s_%s' % (group_prefix, k, v))
            inv[key].append(container.name)

    # return
    print json.dumps(inv, sort_keys=True, indent=2)


if __name__ == '__main__':
    docker_inventory()