ddns-updater-ext 0.1.6

Update DDNS services; extensible

Extensible DDNS Updater

Pushes the possibly changing IP address of a host myhost.mydomain.com to a remote dynamic domain name service (DDNS).

Overview

Usage: a cron job would typically be used at regular intervals to run

sudo <proj-root>/src/lanmanagement/ddns_updater.py <ddns-service-name>

Assuming the program runs on myhost.mydomain.com, it each time:

1. Detects myhost's current IP address
2. Inquires which IP DNS services currently provide for the host
3. If the two IP addresses differ, updates the DDNS service

A rotating log is maintained at

<proj-root>/src/lanmanagement/logs/ddns.log<n>

To obtain a list of supported DDNS services, add the --list (or -l) to the above call.

Implementation

The out-of-the-box implementation can interact with NameCheap's DDNS service. The files utils.py and dns_service.py provide DNS related facilities that can be useful for purposes other than dynamic DNS.

Extending for New DDNS Services

Administrators can extend the implementation to interact with additional DDNS services. The core of these service interactions is to generate a proper URL that instructs the service to update its IP address for myhost.mydomain.com/.net.io,... For each supported service the query parameters are stored as a section of options in a Python configparser .ini file. Like this:

[namecheap]

# Part of URL for updating service before the query parms:
url_root     = https://dynamicdns.park-your-domain.com/update?
secrets_file = $HOME/.ssh/ddns_password
# The query parameters:
host         = myhost
domain       = mydomain.net

Other services might require additional information.

The administrator creates a short subclass, such as NameCheap in ddns_service_adapters.py. The class just needs to provide a single method ddns_update_url(new_ip), which returns a URL suitable to send to the new DDNS service for IP update.

Architecture

The main class is DDNSUpdater. Its constructor takes a DDNS servicename, such as "namecheap". That name is provided as argument when ddns_updater.py is run on the command line, or in a cron job.

The DDNSUpdater requests a handler for the respective DDNS service from a singleton instance of class DDNSServiceManager. This returned handler will be an instance of the subclass mentioned in Extending for New DDNS Services . The DDNSUpdater then calls ddns_update_url() on the handler whenever it determines that the host's IP address has changed. It issues an HTTP request using the returned URL.