Kubernetes Operators Explained: What They Are, How They Work, and How to Build One

What Is a Kubernetes Operator? A Kubernetes Operator is a method of packaging, deploying, and managing a Kubernetes application using custom resources and custom controllers. In concrete terms, an operator is a controller that watches a Custom Resource Definition (CRD) and continuously works to make the actual state of the cluster match the desired state declared in that custom resource. The idea is straightforward: take the operational knowledge that a human engineer would use to run a complex application -- how to deploy it, how to scale it, how to recover from failures, how to handle upgrades -- and encode that knowledge into software that runs inside the cluster. Instead of writing runbooks and hoping someone follows them at 3 AM, you write a controller that handles it automatically. Operators extend the Kubernetes API itself. When you install an operator, you get new resource types (like EtcdCluster or PostgresCluster ) that you can manage with kubectl just like built-in resources