Prometheus

Prometheus scrapes metrics from your services on a schedule, stores them in its own time-series database, and evaluates alerting rules against them. It is the de facto standard that most exporters, charts and tutorials assume.

The pull model and PromQL query language have a learning curve, and long-term storage at scale usually means adding another component (Thanos, Mimir, or remote write). For a homelab, a single instance with node_exporter goes a very long way.

Learn it once and every infrastructure job you touch afterward will feel familiar.