Prometheus

Prometheus is an open-source monitoring and alerting toolkit, originally built at SoundCloud and the second project after Kubernetes to graduate from the CNCF. It stores metrics as time series identified by a metric name and key/value labels, and its query language, PromQL, slices and aggregates those series for graphs, alerts, and recording rules.

Prometheus is pull-based: the server scrapes an HTTP metrics endpoint on each target at a fixed interval, and service discovery for Kubernetes, cloud providers, and Consul keeps the target list current as instances come and go. Applications expose metrics through official client libraries, and hundreds of exporters cover systems that cannot be instrumented directly, such as databases, message queues, and hardware. Alerting rules fire into Alertmanager, which deduplicates, groups, and routes notifications to email, Slack, PagerDuty, and other receivers.

Each server is a single binary with local storage and no clustering, which keeps operations simple but means long-term retention and a global view come from add-ons such as Thanos, Mimir, or VictoriaMetrics through remote write. Grafana is the usual dashboard layer. Prometheus 3, released in November 2024, added a new UI, native OpenTelemetry (OTLP) ingestion, and UTF-8 metric and label names.