Ansible/Hosts/Dynamic Inventory

Example executable dynamic inventory script

Let's walk through an example.

List of hosts:

For vagrant machines, vagrant status gives output about which machines are running. This is information we want to provide to the dynamic inventory file to create a list of hosts.

vagrant status --machine-readable

which is a lot of info in CSV format that can be parsed.

Next, we can use the vagrant ssh-config command, which outputs information that is formatted for an SSH config file, and parse it using pamiko (a Python library for doing SSH-related things - in this case, parsing an SSH config file and turning it into a python dictionary).

#!/usr/bin/env python
# Adapted from Mark Mandel's implementation
# https://github.com/ansible/ansible/blob/stable-2.1/contrib/inventory/vagrant.py
# License: GNU General Public License, Version 3 <http://www.gnu.org/licenses/>
import argparse
import json
import paramiko
import subprocess
import sys


def parse_args():
    parser = argparse.ArgumentParser(description="Vagrant inventory script")
    group = parser.add_mutually_exclusive_group(required=True)
    group.add_argument('--list', action='store_true')
    group.add_argument('--host')
    return parser.parse_args()


def list_running_hosts():
    cmd = "vagrant status --machine-readable"
    status = subprocess.check_output(cmd.split()).rstrip()
    hosts = []
    for line in status.split('\n'):
        (_, host, key, value) = line.split(',')[:4]
        if key == 'state' and value == 'running':
            hosts.append(host)
    return hosts


def get_host_details(host):
    cmd = "vagrant ssh-config {}".format(host)
    p = subprocess.Popen(cmd.split(), stdout=subprocess.PIPE)
    config = paramiko.SSHConfig()
    config.parse(p.stdout)
    c = config.lookup(host)
    return {'ansible_host': c['hostname'],
            'ansible_port': c['port'],
            'ansible_user': c['user'],
            'ansible_private_key_file': c['identityfile'][0]}


def main():
    args = parse_args()
    if args.list:
        hosts = list_running_hosts()
        json.dump({'vagrant': hosts}, sys.stdout)
    else:
        details = get_host_details(args.host)
        json.dump(details, sys.stdout)

if __name__ == '__main__':
    main()