I have the whole question in the Subject. I have a remote server (OpnSense) and I have access to it via Wireguard VPN. On that site I have a bunch of servers running different tasks. One of them feeds FlightRadar24. I got messages that the feed was dead. I attached to that network with Wireguard, and I could ping only the OpnSense server. Looking into the management GUI I discovered that the DNSMasq service was down. I started it and all my other services started to respond after a while.
So my question is: Can OpnSense react to a service not started or having gone down, and send me an email?
There is https://docs.opnsense.org/manual/monit.html but you have to set up what you want to monitor yourself.
This is exactly what I'm looking for. Thanks!