Prometheus is the monitoring system you reach for when you want clear visibility into a distributed system, not just dashboards, but an explainable model for how metrics are collected, stored, queried, and alerted on.

It’s become the default for cloud-native observability because it’s simple at the edges (apps expose /metrics) and powerful at the core (PromQL + alerting), without requiring agents everywhere or a heavyweight centralized pipeline.

It is a complete monitoring system with service discovery, a powerful query language, and sophisticated alerting.

This chapter gives you that depth. We will cover the pull-based architecture, metric types and when to use each, PromQL queries for common patterns, storage internals, alerting strategies, and scaling approaches.

By the end, you will be able to design monitoring into your systems and explain those decisions confidently.

1. When to Choose Prometheus