This is a very barebones server uptime monitoring system. Its original design purpose is to keep tabs on a Beowulf cluster from another location.
There are two components:
The client machines run a cron job at desired intervals to "ping" the server(s) and let it know they're still alive.
NOTE: you must not have PrivateNetwork=yes in your systemd configs for cron, or this process will fail.
The server runs a Python-based webserver in order to accept "pings" from the clients. The server maintains a list of currently known clients and can output them in either over the internet or into a file on request.
The server by default runs on port 55435.
I use this on both a 14-node cluster computer and a 20-node LAN, so if you can come up with an improvement that helps both of us I'll implement it. As is, the codebase is exactly 300 lines of Python, so naturally I can't change that.