Dynamic DNS using AWS

update-dns.py

#!/usr/bin/python

# Run this script as a cron job on a machine inside your network that is always on

# Prerequisites:
# - Python
# - boto3 module for AWS access
# - Route 53 DNS hosted zone that you use as the target
# - SNS topic to send notifications when the DNS is updated (IP changed)
# 
# Assumes that you have the AWS configuration directory available (~/.aws/)
# with a default profile that has API access Route 53 and SNS access

import boto3			# Boto3 library for AWS access
import requests			# Library for making HTTP requests
import socket			# LIbrary for DNS resolution

HOSTZONE = 'AWS_DNS_HOSTED_ZONE_ID'					# AWS hosted zone ID
subject = ""								# SNS subject variable
message = ""								# SNS message body variable
bastion_dns = 'bastion.example.com.'					# DNS hostname to be updated
sns_topic_arn = arn:aws:sns:<region>:<accoundid>:<SNS_Topic_Name>	# The ARN of the SNS topic for notifications

# Create a custom Boto3 session using the default profile
boto3.setup_default_session(profile_name='default')

# Retrieve the current IP address of the bastion DNS hostname
current_bastion_ip = socket.gethostbyname(bastion_dns)

# Get the current IP address of the local host (using AWS checkip address)
current_local_ip = requests.get('http://checkip.amazonaws.com').text.rstrip()

# Route 53 Update Record Set request, with the appropriate IP address and DNS
batch = {
	'Comment': 'Changed by update-dns.py',
	'Changes': [ {
    'Action': 'UPSERT',
    'ResourceRecordSet': {
      'Name': bastion_dns, 'Type': 'A', 'TTL': 60, 'ResourceRecords': [ { 'Value': current_local_ip }, ]
    }
  } ]
}

# If the IP returned by the DNS check is different from the current IP address
if current_bastion_ip != current_local_ip:
	# Create a route53 client session
	client = boto3.client('route53')
	
	# Request an update to the DNS using the batch dict defined earlier
	resp = client.change_resource_record_sets(HostedZoneId=HOSTZONE,ChangeBatch=batch)
	
	# Get the status of the request
	status = resp['ChangeInfo']['Status']
	
	# Set the SNS subject name and message
	subject = "DNS for " + bastion_dns + " changed"
	message = "DNS (" + bastion_dns + ") changed from " + current_bastion_ip + " to " + current_local_ip + "\n"
	message = message + "Status: " + status + "\n"
	
	# Create an SNS resource and Topic object 
	sns = boto3.resource('sns')
	topic = sns.Topic(sns_topic_arn)
	
	# Send the message to the topic
	snsresp = topic.publish(Subject=subject,Message=message)