Update Dynamic DNS record when it's really needed.

ddns_updater.py

#!/usr/bin/python2
# -*- coding: utf-8 -*-
import logging
import os
import re
import subprocess
import sys
import syslog

import dns.resolver


DNS_MASTER = '106.187.55.63'
INSTRUCTION_FILE = '/tmp/ddns_update.txt'


def get_current_ip():
    p = subprocess.Popen('ifconfig ppp0', shell=True, stdout=subprocess.PIPE)
    stdout, _ = p.communicate()

    rc = p.returncode

    m = re.compile('inet (\d+\.\d+\.\d+\.\d+)').search(stdout)
    ip = m.group(1)
    return ip

def update(hostname, ip, zone="momoka.net", ttl=60):

    ins = """
server %(dns_master)s
zone %(zone)s
update del %(hostname)s.%(zone)s. A
update add %(hostname)s.%(zone)s. %(ttl)s A %(ip)s
send
""" % dict(
    dns_master=DNS_MASTER,
    zone=zone,
    hostname=hostname,
    ip=ip,
    ttl=ttl
    )

    with open(INSTRUCTION_FILE, 'w') as f:
        f.write(ins)

    p = subprocess.Popen(
        ('/usr/bin/nsupdate -k '\
         '/root/Kyukari.dyn.areverie.org.+157+27661.private %s') % INSTRUCTION_FILE,
         shell=True,
         stdout=subprocess.PIPE,
         stderr=subprocess.PIPE)

    stdout, stderr = p.communicate()
    os.remove(INSTRUCTION_FILE)
    if p.returncode == 0:
        syslog.syslog('%s.%s updated to %s' % (hostname, zone, ip) )
    else:
        syslog.syslog(syslog.LOG_ERR, '%s.%s updated error: %s' % (hostname, zone, stderr))

def update_momoka(hostname, zone):

    current_ip = get_current_ip()

    r = dns.resolver.Resolver()
    r.nameservers = [DNS_MASTER]

    domain = '%s.%s' % (hostname, zone)

    try:
        a = r.query(domain, 'A')
        result = a[0].to_text()
        if result != current_ip:
            update(hostname, current_ip, zone)
    except dns.resolver.NXDOMAIN:
        update(hostname, current_ip, zone)
    except Exception as err:
        logging.exception(err)
        syslog.syslog(syslog.LOG_ERR, str(err))

def main():
    domains = {
        'momoka.net': ['dyn', 'wiki', 'mirrors', 'maven', 'r', 'reader', 'mail', 'cgit']
    }

    for zone in domains:
        hostnames = domains.get(zone)
        for hostname in hostnames:
            update_momoka(hostname, zone)


if __name__ == '__main__':
    sys.exit(main())