Prometheus

An open-source monitoring system that scrapes metrics endpoints, stores time-series data, and supports powerful PromQL queries. The de facto standard for Kubernetes monitoring.

Prometheus is a intermediate-level concept that sits in the Observability & Monitoring area of system design. Engineers reach for it whenever they need to reason about real-world trade-offs in that space — not just for textbook correctness, but because real production systems at companies like Netflix, Amazon, and Google make these decisions every day.

If you want to go deeper than this definition — with diagrams, code, and a quiz to lock it in — work through the "Prometheus" lesson linked below. It walks through the why, the mechanism, the trade-offs, and how the giants actually use it in production.