Prometheus

Prometheus is a monitoring system and time series database that has become the effective standard for cloud native infrastructure. It is 100 percent open source and community driven, with all components available under the Apache 2 License on GitHub, which means there is no licence cost and no vendor able to change the terms.

Its intellectual lineage is Google's internal Borgmon system. As the Site Reliability Engineering book notes, Borgmon remains internal to Google, but the idea of treating time series data as a data source for generating alerts is now accessible to everyone through open source tools like Prometheus. That idea, alerting computed from queries over time series rather than fixed thresholds on individual checks, is what separates it from earlier monitoring tools.

It was designed for the cloud native world and integrates with Kubernetes and other cloud and container managers to continuously discover and monitor services. That continuous discovery is essential in environments where workloads are created and destroyed constantly and a static list of monitoring targets would be obsolete within minutes.

Prometheus was the second project to graduate from the Cloud Native Computing Foundation, after Kubernetes itself, which is a significant marker of maturity and governance. Hundreds of official and community contributed integrations make it straightforward to extract metrics from existing systems, so adoption rarely requires instrumenting everything from scratch.