dns_change_monitor.py

from contextlib import contextmanager
import time

import dns.resolver
from provisioningserver.utils.twisted import retries


def query_soa(zone):
    for rdata in dns.resolver.query(zone, "SOA"):
        return rdata  # Return the first SOA found.


class DNSChangeTimeOut(Exception):
    """A DNS change was not seen in time."""


@contextmanager
def dns_change_monitor(zone):
    serial = query_soa(zone).serial
    yield
    for elapsed, remaining, wait in retries(15, 0.2):
        if query_soa(zone).serial == serial:
            time.sleep(wait)
        else:
            break
    else:
        raise DNSChangeTimeOut(
            "Changes to %s were not seen." % (zone,))


with dns_change_monitor("my.zone"):
    pass  # Make changes to "my.zone" in MAAS.


# Here changes to "my.zone" will have been loaded by BIND.
pass