🌐 Dynamic DNS

2025-02-16 419 words 2 minutes

Contents

I have a public IP assigned by my ISP, but it is not static, and is therefore subject to change at their whim. This is no good, since I like to be able to access my devices from beyond my local network, and any change in my public IP address will result in misconfigured DNS. A disaster. I need a way to be sure that my any change in my public IP address will trigger an automatic reconfiguration of certain DNS records. I am using AWS Route 53 for my DNS provider, and luckily there is a handy resource available route53-dynamic-dns-with-lambda which perfectly suits my need for DDNS.

Route 53 Dynamic DNS with Lambda

Rather than rehash all of the steps covered in the documentation for this tool, I will simply cover the broad strokes of the process and configuration. The repository linked above basically comes with an installer that walks the user through a few steps to automatically configure the DDNS. The user is left with a simple script that will update the Route 53 DNS records any time the sender IP address changes. This is explained pictographically below.

AWS CloudShell

The guide recommends deploying their Cloud Development Kit using AWS CloudShell session, so this is what I do. The process amounts to cloning the git repo route53-dynamic-dns-with-lambda, running the newrecord.py script contained therein, and following the directions in the CLI bootstrap wizard. The process is basically:

clone the repo
change directory to the repo
install the CDK
run newrecord.py

Generate Configuration File

The last step of the install wizard isa prompt appears to confirm all of the settings.

##############################################
#                                            #
# The following configuration will be saved: #
#                                            #
  Host name:  www.uuard.com
  Hosted zone id: ZYZ12345678901234
  Record set TTL: 60
  Secret: SHARED_SECRET_123
#                                            #
#      do you want to continue? (y/n)        #
#                                            #
##############################################

And finally the following message is produced, along with a dyndns.sh script.

This can be run via a CRON or SystemD timer to periodically update your hostname.

#####################################################
#                                                   #
# The Serverless Dynamic DNS solution is now ready. #
#                                                   #
#####################################################

www.uuard.com can be updated with the following command:
./dyndns.sh -m set -u https://xyz1234567890xyz.lambda-url.eu-west-1.on.aws/ -h www.uuard.com -s SHARED_SECRET_123

The only thing left to be done is to move the provided dyndns.sh script to my server and set up a cron job. I chose to run my script each week “At 00:00 on Sunday” (0 0 * * 0).

Done.