Consider enum instead of boolean for owner_is_controller field

[nmn3m]

What would you like to be added:

Add owner_is_controller field back to owner metrics (or reconsider its implementation as an enum instead of boolean).

Why is this needed:

Currently, multiple owner metrics use owner_is_controller as a boolean label:

• kube_pod_owner
• kube_job_owner
• kube_replicaset_owner
• kube_replicationcontroller_owner
• kube_secret_owner

During review of kube_deployment_owner metric, a question was raised: should this field use an enum instead of boolean to better represent different owner relationship types (e.g., "controller", "application", "custom resource")?

Describe the solution you'd like:

Option 1: Keep boolean implementation

• Use owner_is_controller="true|false" (current implementation for existing metrics)
• Simple and directly maps to Kubernetes OwnerReference.Controller field
• Add this field back to kube_deployment_owner

Option 2: Change to enum

• Use owner_type="controller|application|reference" (or similar)
• More extensible for future owner relationship types
• Requires migration for all existing owner metrics

Additional context:

The kube_deployment_owner metric (#2782) currently has this field removed pending this decision. Once resolved, all owner metrics should be updated consistently for a uniform API.

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[nmn3m]

/cc @CatherineF-dev
/cc @richabanker

[richabanker]

cc @dgrisonnet

[dgrisonnet]

The owner_is_controller field allows for each of the Kubernetes objects you listed, to identify the managing controller. This allows to build an ownership hierarchy. For example:

Deployment
  └── ReplicaSet  (controller=true, owner: Deployment)
        └── Pod   (controller=true, owner: ReplicaSet)

As far as I am aware the other relationship types you listed are not described in the Kubernetes OwnerReference type: https://github.com/kubernetes/kubernetes/blob/ee1ff4866e30ac3685da3e007979b0e9ab7651a6/staging/src/k8s.io/apimachinery/pkg/apis/meta/v1/types.go#L295-L320. The only relationship that is described is the managing controller, so I think that this label still makes sense as it is.

To go back to the topic of Deployments, in vanilla Kubernetes I don't think there could be any controller attached to it since deployments are a top level controller, but in more advanced clusters, there might be custom operators managing deployments and setting this field.

[richabanker]

oh so it is coming from the Kubernetes API. So I guess we cant get rid of it / modify it