Overloaded terms: operator, controller

[samuelebstein]

Could you explain the relationship between controller and operator? It seems that they're being used interchangeably.

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

[k8s-ci-robot]

This issue is currently awaiting triage.

SIG Docs takes a lead on issue triage for this website, but any Kubernetes member can accept issues by applying the triage/accepted label.

The triage/accepted label can be added by org members by writing /triage accepted in a comment.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[lmktfy]

In the page https://kubernetes.io/docs/concepts/extend-kubernetes/operator/ we try to use each term when we mean it.

All operators are controllers, and maybe we could make that point more.
Some controllers are also operators, and maybe we could make that point more too.

---

Outside of Kubernetes docs, people use these terms interchangeably. For example, the operator framework is a library for writing controllers. You can use it to write operators and you can use it to write controllers that are not operators.

There's not much we can do about that wider use.

[shannonxtreme]

@lmktfy is the following generally accurate?

• Controller: an object that tracks the state of the cluster and tries to bring it closer to your desired state.
• Operator pattern: a system design that uses a controller to manage custom resources.
• Operator: a Kubernetes API client that acts performs the work of a controller as part of the operator pattern.