Observability Stack: Prometheus, Node Exporter & Grafana

A solid observability setup usually comes down to three pieces working together: something that collects metrics, something that exposes system-level metrics, and something that visualizes it all. Here's what each one does and how to install them. The Theory: How This All Fits Together Before installing anything, it helps to understand the model, because it's a bit different from how logging or alerting tools usually work. Pull, not push. Most people's first instinct is "the app should send its metrics somewhere." Prometheus flips that around — it pulls metrics on a timer instead. Every target (a machine, a service, an app) exposes a simple HTTP endpoint, usually /metrics , that just returns plain text numbers. Prometheus visits that endpoint every N seconds (the "scrape interval") and saves whatever it finds, with a timestamp attached. Nothing gets pushed to Prometheus — Prometheus goes and asks. This means for anything to show up in Prometheus, it has to satisfy one requirement: something has to expose a /metrics endpoint Prometheus can reach. That's the whole game. Everything else in this stack exists to satisfy that one requirement or to make the data useful afterward. Why Node Exporter exists. Your operating system doesn't naturally speak Prometheus's language — it doesn't expose CPU/memory/disk stats as a /metrics endpoint by default. Node Exporter's only job is to read stats the OS already tracks (via /proc and /sys on Linux) and republish them in the text format Prometheus expects, on port 9100. It's a translator, not a monitoring tool by itself — it collects nothing, decides nothing, alerts on nothing. It just answers "what does this machine look like right now?" whenever asked. Why Prometheus itself is separate. Prometheus doesn't know anything about CPUs or memory — it has no idea what it's scraping. It just knows: "go hit this list of URLs on a schedule, and remember what comes back." The intelligence is in the config (which targets to scrape, how often)