Prometheus

Prometheus is an open-source monitoring and alerting system, not a general-purpose analytics database: it periodically scrapes numeric metrics from applications and infrastructure, stores them in its own built-in time-series database, and evaluates alerting rules against them using its query language, PromQL. It became the default metrics standard for Kubernetes and cloud-native environments, and most application frameworks and infrastructure tools expose a Prometheus-compatible metrics endpoint. Prometheus is designed for short-to-medium retention and operational alerting rather than long-term analytical storage or high cardinality at scale, which is why it is almost always paired with Grafana for visualization and, for longer retention or higher cardinality, with a remote-write-compatible backend such as VictoriaMetrics, Thanos or Cortex. It is self-hosted, single-binary by default, and governed as a graduated project of the Cloud Native Computing Foundation with no official managed cloud offering of its own.