DnsUpdater

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The dns_updater.py script is used to update the A record on a Gandi DNS. Its use may be necessary when you host a server behind an internet box and this one has a dynamic public IP address while you wish to use a domain name hosted by Gandi. This is the case for example in France with the Internet service provider Orange/Sosh.

Features

Here is the list of features:

Updates the IP (A record) of one or more hosts hosted by Gandi,
Send an email when the IP is changed.

Prerequisite

To function properly, dns_updater.py requires a number of prerequisites. The choice of suppliers is left to your choice. An exception concerns the host of the domain name which can only be Gandi, the script is using a REST API call whose format is currently only valid at Gandi.

Here is the list of prerequisites::

An Internet service provider with an Internet box that allows the configuration and use of dynamic DNS services (NO-ip, DynDNS, ChangeIP, ...),
A dynamic DNS service accepted by the Internet box,
A domain name hosted by Gandi,
A server local to your network offering services like web/mail/ftp/...,
A server (which maybe the same) allowing the execution of Python scripts in version 3.

Architecture

Here is a small diagram representing the architecture that will be implemented:

Some explanations are needed on the sequence of the different stages:

When the IP address of the box changes, it warns the dynamic DNS service so that the new IP is associated with dynamic domain names,
A scheduler (for example crontab) triggers the execution of the script dns_updater.py,
The script indirectly queries the dynamic IP service name server (in fact it is the DNS server that the Python scripting server uses, for example that of your ISP),
The script retrieves the IP address associated with the dynamic domain name. If this IP is different from the last retrieval, the sequence is done on step 5, otherwise ends immediately,
The script updates the IP address in the A record of the domain name hosted by Gandi.

Installation

To work, this script requires a computer with Python 3 installed. It is tested and works on Windows and Linux Debian.

It requires the following Python modules:

os
sys
socket
pathlib
configparser
requests
json
datetime
logging
envelopes

If a module is missing, it must be installed using the command: pip3 install <module_name>

Configuration

Settings

When launching the script for the first time, a minimalist dns_updater.ini configuration file is created in the same directory as the script. This file is of the form:

[General]
version=1
#ddnsHostname=DYNAMIC_DNS_HOST
ip=

[Reports]
logFile=dns_updater.log
logFileWhen=midnight
logFileInterval=3600
logFileBackupCount=10

[Email]
#smtpServerHost=SMTP_HOST
smtpServerPort=25
#smtpServerLogin=SMTP_USER_LOGIN
#smtpServerPassword=SMTP_USER_PASSWORD
#emailFromAddress=FROM_EMAIL_ADDRESS
emailFromName=DNSUpdater
#emailTo=YOUR_EMAIL
emailChangeResultSubject=[DNSUpdater] IP address changed

[Gandi]
#apikey=YOUR_GANDI_API_KEY
livednsRecordUrl=https://api.gandi.net/v5/livedns/domains/{host}/records/%%40/A
hosts=YOUR_HOSTS_SEPARATED_BY_COMMA

The script will then end and stop each time as long as the mandatory parameters have not been valued and uncommented.

Section	Setting	Mandatory	Description
General	version	yes	Version of the script for this INI file.
General	ip	no	Will be automatically valued at the first launch when the mandatory parameters have been setted
General	ddnsHostname	yes	The name of the domain hosted in the dynamic domain service (for example: mysite.ddns.net)
Reports	logFile	no	Path to the log file.
Reports	logFileWhen	no	Set when to rotate the file. The possible values are: S (seconds), M (minutes), H (hours), D (days), midnight (rotation at midnight) W{0-6} (days of the week starting with 0 for Monday).
Reports	logFileInterval	no	The interval in seconds, minutes, days, ....
Reports	logFileBackupCount	no	Number of history to keep.
Email	smtpServerHost	no	SMTP host.
Email	smtpServerPort	no**	SMTP port.
Email	smtpServerLogin	no**	User login for this SMTP server.
Email	smtpServerPassword	no**	User password for this SMTP server.
Email	emailFromAddress	no**	Sender email address.
Email	emailFromName	no**	Sender name.
Email	emailTo	no**	Email recipient.
Email	emailChangeResultSubject	no**	Subject for the email sent when the IP address is changed.
Gandi	apikey	yes	Gandi's REST API key. Refer to page https://docs.gandi.net/en/domain_names/advanced_users/api.html
Gandi	livednsRecordUrl	yes	URL for calling the A record update service at Gandi. Normally we don't touch it without knowing what we're doing
Gandi	hosts	yes	The list of domain names at Gandi separated by commas (for example: mysite1.org,mysite2.net,mysite3.com). There should be no space.

* mandatory if logFile is set. ** mandatory if smtpServerHost is set.

Rights

Given the sensitive aspect of the script and its configuration, it is recommended that you only give the execution and modification rights of the script to an administrator. In Linux, this is done as follows:

chown root:root dns_updater.py
chmod 744 dns_updater.py
chown root:root dns_updater.ini
chmod 600 dns_updater.ini

On Windows or other OS, refer to its documentation to learn how to modify these rights.

Scheduling

The scheduling under Linux is done with crontab. Here's how to configure the script to run every 5 minutes. We will assume that the script is at this location: /opt/DnsUpdater/dns_updater.py. To modify crontab for the administrator, do this:

sudo crontab -e

In the editor that appears, add the line:

*/5 * * * * python3 /opt/DnsUpdater/dns_updater.py > /dev/null 2>&1

Bugs & new features

You can report any bugs or request changes and new features using the GitHub's issue manager: https://github.com/stefv/DnsUpdater/issues