How do you monitor your servers?

Running services, network usage, memory usage, bandwidth, disk I/O, successful logins, whether the thing is even alive, etc…
So far my only method has been “hope and pray”.

I have a robust monitoring system for my Jellyfin server, been running for the last few years. Checks in periodically, at least once per 24 hours and notifies me if it’s down. Doesn’t use any electricity, but does consume a good amount of Cheerios and mac & cheese.