To piggy back on the question, has anyone had a good experience using Prometheus and Grafana for monitoring? I'm looking into trying it. I've looked into Zenoss but from what I gather it's slow.
Yes, of course, Its a great tool to track statistics and write alerts. Prometheus is designed to scrape the stats from the services directly, but its also possible to do some kind of active checks. Maybe for checking the ssl cert expiry date you can use the blackbox exporter. https://github.com/prometheus/blackbox_exporter