Dynamic DNS Updates via the Njalla API

1. Njalla's API

As noted in my recent post about switching to Njalla from Cloudflare, I was searching for a way to replace my bash script to update my domain's A record with my home's internet protocol (IP) address dynamically.

To reiterate what I said in those posts, this is a common necessity for those of us who have non-static IP addresses that can change at any moment due to internet service provider (ISP) policy.

In order to keep a home server running smoothly, the server admin needs to have a process to constantly monitor their public IP address and update their domain's DNS records if it changes.

This post explains how to use Python to update Njalla's DNS (domain name system) records whenever a machine's public IP address changes.

1.1. Creating a Token

To use Njalla's API, you will first need to create a token that will be used to authenticate you every time you call the API (application programming interface). Luckily, this is very easy to do if you have an account with Njalla.

Simply go the API Settings page and click the Add Token button. Next, enter a name for the token and click Add.

Finally, click the Manage button next to your newly created token and copy the API Token field.

1.2. Finding the Correct API Request

Once you have a token, you're ready to call the Njalla API for any number of requests. For a full listing of available requests, see the Njalla API Documentation.

For this demo, we are using the list-records and edit-record requests.

The list-records request requires the following payload to be sent when calling the API:

params: {
    domain: string
}

The edit-record request requires the following payload to be sent when calling the API:

params: {
    domain: string
    id: int
    content: string
}

2. Server Set-Up

To create this script, we will be using Python. By default, I use Python 3 on my servers, so please note that I did not test this in Python 2, and I do not know if Python 2 will work for this.

2.1. Creating the Script

First, find a suitable place to create your script. Personally, I just create a directory called ddns in my home directory:

mkdir ~/ddns

Next, create a Python script file:

nano ~/ddns/ddns.py

The following code snippet is quite long, so I won't go into depth on each part. However, I suggest you read through the entire script before running it; it is quite simple and contains comments to help explain each code block.

Note: You will need to update the following variables for this to work:

• token: This is the Njalla API token you created earlier.
• user_domain: This is the top-level domain you want to modify.
• include_subdomains: Set this to True if you also want to modify subdomains found under the TLD (top-level domain).
• subdomains: If include_subdomains = True, you can include your list of subdomains to be modified here.

#!/usr/bin/python
# -*- coding: utf-8 -*-
# Import Python modules

from requests import get
import requests
import json

# Set global variables

url = 'https://njal.la/api/1/'
token = '<your-api-token>'
user_domain = 'example.com'
include_subdomains = True
subdomains = ['one', 'two']


# Main API call function

def njalla(method, **params):
    headers = {'Authorization': 'Njalla ' + token}
    response = requests.post(url, json={'method': method,
                             'params': params}, headers=headers).json()
    if 'result' not in response:
        raise Exception('API Error', response)
    return response['result']


# Gather all DNS records for a domain

def get_records(domain):
    return njalla('list-records', domain=user_domain)


# Update a DNS record for a domain

def update_record(domain, record_id, record_content):
    return njalla('edit-record', domain=domain, id=record_id,
                  content=record_content)


# Get public IP addresses

ipv4 = get('https://api.ipify.org').text
print('IPv4: {}'.format(ipv4))
ipv6 = get('https://api64.ipify.org').text
print('IPv6: {}'.format(ipv6))

# Call API to get all DNS records

data = get_records(user_domain)

# Loop through records and check if each one is IPv4 (A) or IPv6 (AAAA)
# Update only if DNS is different from server IP

for record in data['records']:
    if record['name'] == '@' or (include_subdomains and record['name'] \
        in subdomains):
        if record['type'] == 'A':
            if record['content'] == ipv4:
                print(record['type'], 'record for', record['name'],
                      'already matches public IPv4 address. Skipping...'
                      )
            else:
                print('IPv4 of', ipv4,
                      'does not match Njalla's value of',
                      record['content'], '. Updating...')
                update_record(user_domain, record['id'], ipv4)
        elif record['type'] == 'AAAA':
            if record['content'] == ipv6:
                print(record['type'], 'record for', record['name'],
                      'already matches public IPv6 address. Skipping...'
                      )
            else:
                print('IPv6 of', ipv6,
                      'does not match Njalla's value of',
                      record['content'], '. Updating...')
                update_record(user_domain, record['id'], ipv6)

2.2. Running the Script

Once you've created the script and are ready to test it, run the following command:

python3 ~/ddns/ddns.py

2.3. Setting the Script to Run Automatically

To make sure the scripts run automatically, add it to the cron file so that it will run on a schedule. To do this, open the cron file:

crontab -e

In the cron file, paste the following at the bottom of the editor in order to check the IP every five minutes:

*/5 * * * * python3 /home/<your_username>/ddns/ddns.py