IP-Monitor

A basic Golang daemon which detects changes of the local IP or a DNS address.

If a change is detected the configured triggers (e.g. scripts) are executed with the old and the new IP address as parameters.

Installation

1. Download and unpack appropriate release to e.g. /usr/local/bin/ip-monitor
2. Register and Enable as Systemd service. An example unit file can be found under etc/ in this repository
3. Alternatively: (Enable as SysVinit service. An example init script can be found under etc/ in this repository)
4. Configure as described below. An example configuration file can be found under etc/ in this repository
5. Start and check journal logs (Systemd) or logfile (SysVinit)

Configuration

The JSON config file format allows to configure several monitors with one or more triggers each.

Main Section

Key	Value	Comment
log_level	string(info|debug)	Log level of daemon process
log_timestamps	bool	Timestamps in log output. Useful if running with SysVinit
interval	int()	Monitor interval in seconds. A too low value might cause a Service/DNS provider ban
http_provider	string()	URL of the HTTP IP provider to use. Must respond only with an IP address string

Monitors Section

Key	Value	Comment
name	string()	Friendly monitor name for log output
domain	string()	DNS address to monitor. If empty HTTP mode is used = Local IP address
ip_version	string(ip4|ip6)	Define if IPv4 or IPv6 address of domain should be monitored
triggers	list(string)	Path to the trigger scripts or executables. Can be one or many.

Modes of operation

As described above the daemon can monitor IP address changes via HTTP or DNS.

In the HTTP mode usually only local Internet IP address changes can be detected, while in DNS mode any system can be monitored which populates a DNS address.

Warning It is expected that only one IP address is populated via DNS for a domain. If multiple hosts can be found at a time, an error will be logged and the trigger will not be executed because of unpredictable results.

Use cases

HTTP mode

Useful to monitor local Internet IP address changes. "If my local Internet IP address changes I would like to automatically perform action ..."

DNS mode

Useful to monitor remote IP changes. "My router automatically updates a DynDNS address. If the address changes I would like to automatically perform action ..."

Triggers

Triggers are executables or scripts which get executed once an IP address change is detected. The daemon will execute those as follows:

/path/to/executable $OLD_IP $NEW_IP

This allows you to script what needs to be done on the system. Examples would be:

• iptables changes
• Configuration changes of service
• Service restarts
• Send an email
• ...

Trigger scripts must be executable and in case of scripts contain a Shebang.

Example

#!/bin/bash

echo "Old IP was: $1"
echo "New IP is: $2"

Key concepts

• Allow to configure several monitors with several triggers each
• Avoid to use the local DNS cache
• Use HTTP or DNS resolvers
• Support IPv4 and IPv6 scenarios

Disclaimer

The daemon is only tested on Debian and Ubuntu Linux. It might work on Darwin, MacOS or other Linux distributions as well.