I have a very simple setup here (solo IT guy): we have a on-prem server which runs some services. They should produce e.g. a daily logfile. I'd like to get a notification if this doesn't happen for some reason. I make a script, activated from cron, that checks this and sends me an email if it doesn't happen. However, this obviously doesn't work if e.g. the entire server goes down, my email script has a bug, etc, so I'd like to have the converse: have a daily check and get an email if it did NOT ran. I do have this with www.duplicati-monitoring.com: I get an email even if my on-prem server is down. I'd like to extend this to more infrastructure tests.
How is such a system called? Are there websites (preferrably free / open source) offering this? I looked at eg nagios, but it seems far too big, and it seems that I need to host it myself.