Dynamic DNS

A simple utility to update an existing DNS record on Cloudflare when the public IP changes.

Working

The main working is in the ddns script.

The script gets the public IP from ipinfo.io/ip and conducts a rudimentary IP RegEx check.

The script stores the previously used public IP address in a file called public-ip-in-use.txt. (Obviously this file does not exist when the script is run for the first time.)

The script compares the newly found public IP address and the previously used IP address stored in public-ip-in-use.txt. If the IP addresses are the same, then it does nothing, but if the IP addresses don't match, it replaces the IP address in the public-ip-in-use.txt file with the newly found IP address, and updates it on Cloudflare as well.

A CRON job runs this script every 10 minutes, so that the DNS record on Cloudflare always has the current public IP address.

Usage

• Clone the repository.

  $ cd ~
  $ git clone https://github.com/HarshKapadia2/dynamic-dns.git

• On the Cloudflare dashboard, create a new A record with a dummy IP address. Turn off Cloudflare's proxying for that DNS record and leave it at 'DNS Only'.

• In the repository, create two files run-ddns and list-all-dns-records, add content to it as described in the run-ddns and list-all-dns-records sections, and give them executable permissions.

  $ cd ~/dynamic-ddns
  $ vim run-ddns # Add content from the 'run-ddns' section below.
  $ vim list-all-dns-records # Add content from the 'list-all-dns-records' section below.
  $ sudo chmod +x run-ddns
  $ sudo chmod +x list-all-dns-records

• Run the list-all-dns-records script and make a note of the Record ID of the DNS record to be updated. Add that to the run-ddns script.

• Follow the instructions in the 'CRON Script' section to set up a CRON job that will run the run-ddns script periodically, so that the DNS record on Cloudflare always has the current public IP address.

Scripts

run-ddns

This script is used to provide sensitive variables to the ddns script and then run it.

NOTE:

• Cloudflare Zone ID
• Cloudflare API Token
• The Cloudflare Record ID can be found by running the list-all-dns-records script.

#! /bin/bash

set -Eeuo pipefail

# Set 'dynamic-dns' repository directory path
ddns_repo_path="$(dirname "$0")"

if [[ "${ddns_repo_path}" == "." ]]; then
	ddns_repo_path="$(pwd)"
fi

# Provide environment variables and run `ddns` script
CLOUDFLARE_ZONE_ID="<zone_id_here>" \
	CLOUDFLARE_AUTH_KEY="<api_token_here>" \
	CLOUDFLARE_DNS_RECORD_NAME="<[subdomain.]domainname.tld>" \
	CLOUDFLARE_DNS_RECORD_ID="<id_of_record_to_be_updated_here>" \
	bash "${ddns_repo_path}/ddns"

Setting environment variables just for one command/script

CRON Script

In Ubuntu, this script is to be placed at /etc/cron.d/dynamic-dns. It runs a CRON job every 10 minutes to run the run-ddns script.

NOTE: Replace the HOME variable with the path to the dynamic-dns repo location. Also, replace the <username> with the name of the user that should run the script (root or any other user).

# This is to set up a public IP address.
SHELL=/bin/bash
HOME=/home/harsh/dynamic-dns
#
*/10 * * * * <username> ./run-ddns

list-all-dns-records

This script lists information about all DNS records. It is used to to get the Record ID of the DNS record that needs to be updated by the ddns script.

NOTE:

• Cloudflare Zone ID
• Cloudflare API Token

#! /bin/bash

set -Eeuo pipefail

CLOUDFLARE_ZONE_ID="<zone_id_here>"
CLOUDFLARE_AUTH_KEY="<api_token_here>"

curl --request GET \
	--url "https://api.cloudflare.com/client/v4/zones/${CLOUDFLARE_ZONE_ID}/dns_records" \
	--header "Content-Type: application/json" \
	--header "Authorization: Bearer ${CLOUDFLARE_AUTH_KEY}"

Resources

• What Is Dynamic DNS (DDNS), and How Do You Set It Up?
• How to Setup Cloudflare Dynamic DNS
• CRON Jobs
  • Scheduling Cron Jobs with Crontab
  • How to Run Cron Jobs Every 5, 10, or 15 Minutes
  • Creating a file in /etc/cron.d
  • How to view a cron job running currently?