It's a best practice with Prometheus that target labels should be constant over a target's entire lifetime. On the other hand it's useful to aggregate metrics across all the machines that are currently Apache servers. How can we do that?
Reliable Insights
A blog on monitoring, scale and operational Sanity
CPU, RAM, disk and network usage are basic machine metrics you should be monitoring. This is easy with Prometheus and the later releases of Debian.
Sometimes you need a machine metric that's not exported yet by the node exporter. The textfile collector can be used to quickly get such metrics graphed in Prometheus.
