Goal

• Document how user-defined monitoring administrators can define PrometheusRules objects spanning multiple/all user namespaces.

Why is this important?

• There's often a need to define similar alerting rules for multiple user namespaces (typically when the rule works on platform metrics such as kube-state-metrics or kubelet metrics).
• In the current situation, such rule would have to be duplicated in each user namespace which doesn't scale well:
  • 100 expressions selecting 1 namespace each are more expensive than 1 expression selecting 100 namespaces.
  • updating 100 PrometheusRule resources is more time-consuming and error-prone than updating 1 PrometheusRule object.

Scenarios

1. A user-defined monitoring admin can provision a PrometheusRules object for which the PromQL expressions aren't scoped to the namespace where the object is defined.