Dynamic DNS with Route53

dynamic_dns_route53.py

#! /usr/bin/env python3

"""
Dynamic DNS - Route53

Check the current IP address for this device and compare it with the DNS record
in Route53. If it's different, update the DNS record!
"""

import logging
import os
import re
import sys

import boto3
import requests

logging.basicConfig(
    format="%(asctime)s %(levelname)-8s %(message)s",
    level=logging.INFO,
    datefmt="%Y-%m-%d %H:%M:%S"
)
LOG = logging.getLogger('dynamic-dns')
RE_IP_ADDRESS = re.compile(r'\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}')
HOSTED_ZONE_ID = os.getenv('HOSTED_ZONE_ID')
RECORD_NAME = os.getenv('RECORD_NAME')


if __name__ == '__main__':
    LOG.debug('Starting dynamic-dns')

    # Require HostedZone ID
    LOG.debug('Verifying HostedZone ID')
    if HOSTED_ZONE_ID is None:
        LOG.warning('Missing HostedZone ID')
        sys.exit(1)
        
    # Require HostedZone ID
    LOG.debug('Verifying record name')
    if RECORD_NAME is None:
        LOG.warning('Missing record name')
        sys.exit(1)

    # Check the current public IP address
    LOG.debug('Retrieving current public IP address')
    current_ip = requests.get('http://checkip.amazonaws.com').text.strip()
    LOG.debug('Current public IP address: %s', current_ip)

    # Validate the current public IP address
    LOG.debug('Validating current public IP address')
    if not RE_IP_ADDRESS.match(current_ip):
        LOG.warning('Invalid IP address: %s', current_ip)
        sys.exit(2)

    # Cross-check the current DNS record
    LOG.debug('Retrieving current DNS')
    route53 = boto3.client('route53')
    all_records = route53.list_resource_record_sets(
        HostedZoneId=HOSTED_ZONE_ID
    ).get('ResourceRecordSets', [])
    current_record = None
    for record in all_records:
        if record['Name'] == RECORD_NAME:
            current_record = record
            break
 
    # Check for changes
    LOG.debug('Checking current DNS against current IP address')
    if current_record['ResourceRecords'][0]['Value'] == current_ip:
        LOG.info('DNS is up-to-date. Exiting...')
        sys.exit()

    # Update the DNS
    LOG.debug('Updating DNS')
    route53.change_resource_record_sets(
        HostedZoneId=HOSTED_ZONE_ID,
        ChangeBatch={
            'Comment': 'Updated using dynamic_dns_route53.py',
            'Changes': [{
                'Action': 'UPSERT',
                'ResourceRecordSet': {
                    'Name': record['Name'],
                    'Type': record['Type'],
                    'TTL': 300,
                    'ResourceRecords': [{
                        'Value': current_ip
                    }]
                }
            }]
        }
    )
    
    LOG.info('Updated DNS successfully: %s', current_ip)
    sys.exit()

Instructions

1. Install this script onto any device on your network with access to the public interwebs
2. pip3 install requests boto3
3. Configure AWS credentials via a profile
4. Add the following line to your device's crontab

* * * * * AWS_PROFILE=profile HOSTED_ZONE_ID=zone_id RECORD_NAME=record_name /path/to/python3 /path/to/dynamic_dns_route53.py