updateip.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# Update Route53 DNS A name record for home IP.
#
# Uses the *route53* library, rather than boto.
from __future__ import print_function

import os
import re
import sys

import requests
import route53
import route53.exceptions


try:
    TARGET_RRSET_NAME = os.environ['TARGET_RRSET_NAME']
    AWS_ACCESS_KEY_ID = os.environ['AWS_ACCESS_KEY_ID']
    AWS_SECRET_ACCESS_KEY = os.environ['AWS_SECRET_ACCESS_KEY']
except KeyError:
    print('Set TARGET_RRSET_NAME, AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY',
          file=sys.stderr)
    sys.exit(1)

HOSTED_ZONE = '.'.join(TARGET_RRSET_NAME.split('.')[1:])
if not HOSTED_ZONE.endswith('.'):
    print('TARGET_RRSET_NAME should be of the form host.domain.com.',
          file=sys.stderr)
    sys.exit(1)


def fetch_external_ip():
    """Use https://ip.appspot.com/ to determine external IP address.

    """

    try:
        req = requests.get('https://ip.appspot.com/', timeout=5)
    except requests.exceptions.Timeout:
        print('Service timed out!',
              file=sys.stderr)
        sys.exit(1)
    except Exception, exc:
        print('Something happened! ', exc,
              file=sys.stderr)
        sys.exit(1)

    if req.status_code != 200:
        print('Service returned {}!'.format(req.status_code),
              file=sys.stderr)
        sys.exit(1)

    ip_addr = req.content.strip()
    return ip_addr


def main(home_ip):
    """Retrieve external IP from home ADSL router then compare it with a
    DNS record and, if they do not match, update the DNS record (via
    AWS Route53) so they match.

    """

    try:
        conn = route53.connect(
            aws_access_key_id=AWS_ACCESS_KEY_ID,
            aws_secret_access_key=AWS_SECRET_ACCESS_KEY)

        try:
            # list zones, and pull out the one we're interested in
            zone = [zone
                    for zone in conn.list_hosted_zones()
                    if zone.name == HOSTED_ZONE][0]
        except IndexError:
            print('No such Hosted Zone {}'.format(HOSTED_ZONE),
                  file=sys.stderr)
            sys.exit(1)

        try:
            # get and save changes to an existing RR set…
            rr_set = [rr_set
                      for rr_set in zone.record_sets
                      if rr_set.name == TARGET_RRSET_NAME \
                        and rr_set.rrset_type == 'A'][0]
            # FIXME can rr_set.values ever be an empty list?!
            if rr_set.records[0] == home_ip:
                # IP hasn't changed, exit quietly
                sys.exit()
            else:
                # update the record!
                rr_set.records = [home_ip]
                rr_set.save()
        except IndexError:
            # create a new RR set.  note this will fail if a RRSet of
            # the same name but different type exists…
            new_record, change_info = zone.create_a_record(
                name = TARGET_RRSET_NAME,
                values = [home_ip],
                ttl = 300)
        print('A record {} now points to {}'.format(
            TARGET_RRSET_NAME, home_ip))

    except route53.exceptions.Route53Error, exc:
        print('Something went wrong', exc,
              file=sys.stderr)
        sys.exit(1)


if __name__ == '__main__':
    home_ip = fetch_external_ip()
    main(home_ip)