Libvirt with domain and resolvectl

network.py

#!/usr/bin/env python3

# https://www.libvirt.org/hooks.html#network
# Place this as /etc/libvirt/hooks/network

import logging
import sys
from argparse import ArgumentParser
from subprocess import CalledProcessError, check_output

from xml.etree.ElementTree import ElementTree, fromstring, parse, dump
from xml.etree import ElementTree


logger = logging.getLogger('network-hook')


def read_xml(path: str) -> ElementTree.Element:
    if path == '-':
        root = ElementTree.fromstring(sys.stdin.read())
        return root.find('network')
    else:
        with open(path) as f:
            return ElementTree.parse(f)


def handle_xml(xml: ElementTree) -> None:
    domain = xml.find('domain')
    if domain is None:
        logger.debug('No domain found')
        return

    domain_name = domain.attrib['name']
    if domain_name is None:
        logger.debug('No domain name found')
        return

    bridge = xml.find('bridge')
    if bridge is None:
        logger.debug('No bridge found')
        return

    interface = bridge.attrib['name']
    if interface is None:
        logger.debug('No interface found')
        return

    ip = xml.find('ip')
    if ip is None:
        logger.debug('No ip found')
        return

    ip_address = ip.attrib['address']
    if ip_address is None:
        logger.debug('No address found')
        return

    set_resolver(interface, ip_address, domain_name)


def set_resolver(interface: str, ip: str, domain: str) -> None:
    logger.info('Setting resolver on %s to %s with %s', interface, ip, domain)

    try:
        check_output(['resolvectl', 'dns', interface, ip])
    except CalledProcessError:
        logger.exception('Failed to set DNS resolver on interface %s to %s', interface, ip)

    try:
        check_output(['resolvectl', 'domain', interface, domain])
    except CalledProcessError:
        logger.exception('Failed to set DNS domain on interface %s to %s', interface, domain)


def main():
    logging.basicConfig(level=logging.DEBUG)

    parser = ArgumentParser()
    parser.add_argument('network_name')
    parser.add_argument('action')
    parser.add_argument('phase')
    parser.add_argument('xml')

    args = parser.parse_args()
    if args.action == 'started':
        try:
            xml = read_xml(args.xml)
        except:
            logger.exception('Failed to read XML from %s', args.xml)
            raise
        handle_xml(xml)


if __name__ == '__main__':
    main()

network.xml

<network xmlns:dnsmasq='http://libvirt.org/schemas/network/dnsmasq/1.0'>
  <bridge name='virbr0' stp='on' delay='0'/>
  <!-- change your domain name here -->
  <domain name="sub.example.com" localOnly="yes"/>
  <ip address='192.168.122.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='192.168.122.2' end='192.168.122.254'/>
    </dhcp>
  </ip>
</network>