Operator

Operator: A Kubernetes software extension using Custom Resources (CRs) and a control loop to automate the full application lifecycle (Day 2 operations).

We deploy the Operator pattern to extend core Kubernetes functionality: it acts as an application-specific controller, automating complex workloads. The core mechanism leverages Custom Resource Definitions (CRDs) to capture domain-specific knowledge (like for a MySQL or Prometheus instance). You declare the desired state in the CRD; the Operator’s control loop then continuously reconciles reality to match that specification. This automation handles critical Day 2 operations—specifically: automated backups, version upgrades, and failover logic, ensuring consistency and reducing manual toil across your cluster.

https://kubernetes.io/docs/concepts/extend-kubernetes/operator-pattern/