Kubernetes Operator - toge510/homelab GitHub Wiki
Operator
Operators are software extensions to Kubernetes that make use of custom resources to manage applications and their components. Operators follow Kubernetes principles, notably the control loop.
The Operator pattern combines custom resources and custom controllers. You can use custom controllers to encode domain knowledge for specific applications into an extension of the Kubernetes API.
Custom resource and Custom controller
A resource is an endpoint in the Kubernetes API that stores a collection of API objects of a certain kind; for example, the built-in pods resource contains a collection of Pod objects.
A custom resource is an extension of the Kubernetes API that is not necessarily available in a default Kubernetes installation. Once a custom resource is installed, users can create and access its objects using kubectl, just as they do for built-in resources like Pods.
Custom resources let you store and retrieve structured data. When you combine a custom resource with a custom controller, custom resources provide a true declarative API.
Controllers are infinite loops that watch the actual and the desired states of your cluster. When these two states diverge, controllers start making changes aiming to bring the current state of the cluster closer to the desired one.
Custom controllers can work with any kind of resource, but they are especially effective when combined with custom resources.