[mcpherrinm]

I run the Prometheus node_exporter on my servers. That has a systemd collector for the state of services.

That reports the state of all systemd services to a central Prometheus and alertmanager cluster, which has various alert rules.

[pphysch]

I recommend this approach, as you can also deploy blackbox_exporter to get an "outside" perspective on service status.

[scrapheap]

You can also restrict the list of systemd services that node_exporter provides metrics for - that way you only store metrics for those services you care about.