Kubernetes Operators and CRDs.

Operators encapsulate operational domain knowledge into software to automate the lifecycle of complex stateful applications in K8s.

A Custom Resource Definition (CRD) extends the Kubernetes API with custom objects (e.g., kind: PostgreSQLCluster). The Operator is a custom controller pod running a reconciliation loop. It watches for changes to these CRDs and makes APIs calls to bring the real cluster state into the desired state defined by the CRD.