Prometheus

Prometheus is a monitoring system and time-series database originally built at SoundCloud in 2012. It became the second project to graduate from the Cloud Native Computing Foundation (after Kubernetes) and has since become the standard for monitoring cloud-native infrastructure. Unlike push-based systems, Prometheus pulls metrics by scraping HTTP endpoints on instrumented services at configured intervals.

The current major release is Prometheus 3. Metrics are stored in an efficient local time-series database and queried with PromQL, a purpose-built query language for selecting, aggregating, and transforming time-series data. Service discovery integrations (Kubernetes, Consul, DNS, file-based) automatically find scrape targets as infrastructure changes. Alertmanager handles alert routing, deduplication, and silencing. Prometheus defines the OpenMetrics exposition format, which has become the standard for metrics instrumentation across languages.

The official documentation covers configuration, PromQL, and client library instrumentation. The source code is on GitHub under the Apache 2.0 license.