feat: Adds category label for unschedulable pod as part of kube_pod_status_unschedulable metric

[ilaylow]

What this PR does / why we need it:

This PR allows us to determine if a pod's reason for being unschedulable by introducing a custom category label:

• RESOURCE - Pod is unschedulable due to insufficient resources.
• AFFINITY - Pod is unschedulable due to pod affinity.
• UNKNOWN - Pod is unschedulable due to unknown reasons.

The category is derived from making assumptions on the the PodCondition.Message value (see below).

// PodCondition contains details for the current condition of this pod.
type PodCondition struct {
	...
	// Human-readable message indicating details about last transition.
	// +optional
	Message string `json:"message,omitempty" protobuf:"bytes,6,opt,name=message"`
        ...
}

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)

Increases cardinality mildly due to the addition of a label with 3 dimensions.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
(No ongoing issue)

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: ilaylow / name: Chuen Ley Low (55f1712, f5fd9d4, 99d0fb6)

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: ilaylow
Once this PR has been reviewed and has the lgtm label, please assign dgrisonnet for approval. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[k8s-ci-robot]

This issue is currently awaiting triage.

If kube-state-metrics contributors determine this is a relevant issue, they will accept it by applying the triage/accepted label and provide further guidance.

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.

[k8s-ci-robot]

Welcome @ilaylow!

It looks like this is your first PR to kubernetes/kube-state-metrics 🎉. Please refer to our pull request process documentation to help your PR have a smooth ride to approval.

You will be prompted by a bot to use commands during the review process. Do not be afraid to follow the prompts! It is okay to experiment. Here is the bot commands documentation.

You can also check if kubernetes/kube-state-metrics has its own contribution guidelines.

You may want to refer to our testing guide if you run into trouble with your tests not passing.

If you are having difficulty getting your pull request seen, please follow the recommended escalation practices. Also, for tips and tricks in the contribution process you may want to read the Kubernetes contributor cheat sheet. We want to make sure your contribution gets all the attention it needs!

Thank you, and welcome to Kubernetes. 😃

[mrueg]

Thanks for the PR. We omitted the message on purpose as it can cause high cardinality due to the fact it's not limited to a specific set of messages, so this is a feature we cannot include.

[ilaylow]

Thanks for the PR. We omitted the message on purpose as it can cause high cardinality due to the fact it's not limited to a specific set of messages, so this is a feature we cannot include.

@mrueg

Ah I figured that would be the case. Would you be open to me introducing categorisation to a limited set of values then?

What I'm really looking to get out of this is a way to distinguish between whether a pod was unschedulable due to insufficient resources, or due to pod affinities etc.

[ilaylow]

Thanks for the PR. We omitted the message on purpose as it can cause high cardinality due to the fact it's not limited to a specific set of messages, so this is a feature we cannot include.

@mrueg

I added a naive example implementation in my latest commit 99d0fb6 to address the cardinality issue, could I get your thoughts on this?

[dgrisonnet]

KMS is direct mapping of Kubernetes object to metrics, it exposes the data as is without any modification. Also, maintaining an updated list of categories would be quite painful from a maintainer perspective