Dynamic DNS with CloudFlare

This is a simple hack I found for my self to have a “Dynamic DNS” for my home IP.

I’m using CloudFlare as my name server to manage the zone file for my domain, And one of the nice things about CloudFlare is that they have nice API to manage your account. One of the options this API provides is the capability to update you DNS entries in the Zone.

** Note: CloudFlare updated there API and the above script may not work for you, but the basic idea is still the same. Check the comment bellow for other users scripts.

Get your token

To preform actions with the API you’ll need 3 things,

• your privet token (called tkn in the API),
• email
• and the action you like to perform.

You can find your token under your Account page

DNS Record ID

Next you’ll need to find the action you like to perform, in my case is to edit the zone file. which is under the “DNS Record Management” -> rec_edit menu, but for using this action you will need the ID number for the record you like to change, and for that you will need to use “rec_load_all” action.

e.g

curl https://www.cloudflare.com/api_json.html \
  -d 'a=rec_load_all' \
  -d 'tkn=8afbe6dea02407989af4dd4c97bb6e25' \
  -d '[email protected]' \
  -d 'z=example.com'

The output will be in a JSON format, and the part you are looking for will look similar to this,

...
{
    "rec_id": "18136402",
    "rec_tag": "3bcef45cdf5b7638b13cfb89f1b6e716",
    "zone_name": "example.com",
    "name": "test.example.com",
    "display_name": "test",
    "type": "A",
    "prio": null,
    "content": "[server IP]",
    "display_content": "[server IP]",
    "ttl": "1",
    "ttl_ceil": 86400,
    "ssl_id": null,
    "ssl_status": null,
    "ssl_expires_on": null,
    "auto_ttl": 1,
    "service_mode": "0",
    -
    "props": {
        "proxiable": 1,
        "cloud_on": 0,
        "cf_open": 1,
        "ssl": 0,
        "expired_ssl": 0,
        "expiring_ssl": 0,
        "pending_ssl": 0
    }
...

Edit/Update the DNS record

Now that you have the ID for the record you like to change, it’s a matter of a simple curl command,

curl https://www.cloudflare.com/api_json.html \
  -d 'a=rec_edit' \
  -d 'tkn=8afbe6dea02407989af4dd4c97bb6e25' \
  -d 'id=18136402' \
  -d '[email protected]' \
  -d 'z=example.com' \
  -d 'type=A' \
  -d 'name=test' \
  -d 'content=1.2.3.4' \
  -d 'service_mode=0' \
  -d 'ttl=1'

This command will update the IP to 1.2.3.4 for test.example.com entry.

Automate the update process

To automate the process, I have a script which runs every time I connect to my home network via NetworkManager, and query my external IP and compare it to the resolved IP form my DNS, If you need this for your home server, just call the script via cron job or systemd timer.

#!/bin/bash

CURRENT_IP=$(dig myip.opendns.com @resolver1.opendns.com +short)
RESOLVE_IP=$(dig dyn.example.com +short @jean.ns.cloudflare.com)

if [[ ${CURRENT_IP} != ${RESOLVE_IP} ]] ;
then
    echo "need to update IP from: ${RESOLVE_IP} -> ${CURRENT_IP}"
    curl https://www.cloudflare.com/api_json.html -d 'a=rec_edit' \
        -d 'tkn=c7ee1aef8131daf52e103a21a786ecbd99193' \
        -d '[email protected]' \
        -d 'id=42' \
        -d 'z=example.com' \
        -d 'type=A' \
        -d 'name=dyn' \
        -d 'content='${CURRENT_IP} \
        -d 'service_mode=0' \
        -d 'ttl=120' \


else
    echo "nothing to do"
    exit 0;
fi