User:Datagrok/ddns

ddns.py is a small script that maintains a DNS record that points at one's home network. This process is sometimes called Dynamic DNS.

There are others like it; see The DNS section of API Apps or Dynamic DNS for some. I wrote this one to obtain the following features that I could not find elsewhere:

• It runs from your DreamHost shell account, and uses your ssh connection to determine your IP.
• It's implemented in Python.
• Uses my own Python module to interface with the DreamHost API.

ddns.py listing:

#!/usr/bin/python -O

from dreamhostapi import DreamHostServerProxy
from os import environ

def main():
    dh_api_key = '6SHU5P2HLDAYECUM'
    hostname = 'home.mydomain.com'

    new_ip = environ['SSH_CLIENT'].split()[0]
    server = DreamHostServerProxy(dh_api_key)

    if __debug__:
        print "Retrieving list of current domains..."

    for record in server.dns.list_records():
        if not (record['record'] == hostname and record['type'] == 'A'):
            continue
        if record['value'] == new_ip:
            if __debug__:
                print "Old record for %(record)s found with IP %(value)s, no update needed." % record
            raise SystemExit()
        if __debug__:
            print "Old record for %(record)s found with IP %(value)s, removing." % record
        result = server.dns.remove_record(
            record=record['record'],
            type=record['type'],
            value=record['value'],
        )

    result = server.dns.add_record(
        comment='Dynamic DNS IP',
        record=hostname,
        type='A',
        value=new_ip,
    )

    if result != 'record_added':
        raise ValueError("There was a problem adding the record.")

    if __debug__:
        print "Success"


if __name__=="__main__":
    main()

Required module

dreamhostapi.py is a small Python module I wrote to interface with the DreamHost API. There are others like it; DreamPyLib is one such. I wrote this one to obtain the following features that I could not find elsewhere:

• It is implemented as a wrapper around Python's built-in XMLRPC library.
• It's short.

dreamhost.api listing:

from xmlrpclib import ServerProxy, _Method
from uuid import uuid1

class DreamHostMethod(_Method):

    def __init__(self, send, name):
        _Method.__init__(self, send, name)

    def __getattr__(self, name):
        return DreamHostMethod(self._Method__send, "%s-%s" % (self._Method__name, name))

    def __call__(self, **kw):
        return self._Method__send(self._Method__name, kw)

class DreamHostServerProxy(ServerProxy):

    dh_api_server = 'https://api.dreamhost.com/xmlrpc'

    def __init__(self, key, verbose=0):
        ServerProxy.__init__(self, uri=self.dh_api_server, verbose=verbose)
        self.dh_api_key = key

    def __getattr__(self, name):
        return DreamHostMethod(self.__request, name)

    def __request(self, name, params):
        if not params:
            params = {}
        params['key'] = self.dh_api_key
        params['uuid'] = str(uuid1())
        result = ServerProxy._ServerProxy__request(self, name, (params,))
        if result['result'] != 'success':
            raise ValueError("Server returned %(result)s: %(data)s" % result)
        return result['data']

Installation

1. Copy the text above for ddns.py to a file named ddns.py on your DreamHost webserver.
2. Change the variables dh_api_key and hostname to whatever you're using.
3. Make it executable. (chmod +x ddns.py)
4. Copy the text above for dreamhostapi.py to a file named dreamhostapi.py on your DreamHost webserver.
5. Set up a machine within your home network to periodically connect to your shell account and run the ddns.py script.

Advanced Installation

I prefer to keep dreamhostapi.py in ~/lib/python/datagrok/; ~/lib/python is in my $PYTHONPATH. I then change the import statement to read:

from datagrok.dreamhostapi import DreamHostServerProxy

I set this to run periodically by creating an executable script /etc/cron.daily/ddns-update on a local machine:

#!/bin/sh
ssh mydomain.com "ddns.py"

Replace mydomain.com everywhere with your own domain name.

For better security, create a separate ssh key just for this automatic process, then restrict the key to run only ddns.py in .ssh/authorized_keys on your DreamHost shell account.