Add ingressclass to kube_ingress_info metric

[adammw]

What this PR does / why we need it:
Add ingressclass to kube_ingress_info metric

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)
Should be same cardinality since it adds a tag to an existing metric that is already one per resource.

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[fpetkovski]

@dgrisonnet @mrueg do we have any conventions about adding labels to stable metrics? It might break existing rules and queries that use aggregations.

[mrueg]

No official guidelines exist I believe. Since this is an info metric, I'd assume folks extract labels from it and I think the risk of breaking anyones workflow there by adding a new label is low. Also it would be part of a new minor/feature release.

[fpetkovski]

Thanks Manuel, this makes sense to me.

@adammw I noticed that the ingress class label is determined from an annotation value. Is there any reason why you cannot use the --metric-annotations-allowlist flag to expose the ingress class annotation? Also, Kubernetes has already made ingress class a first order citizen [1] and that specific annotation has been declared deprecated [2].

[1] https://kubernetes.io/docs/concepts/services-networking/ingress/#ingress-class
[2] https://kubernetes.io/docs/concepts/services-networking/ingress/#deprecated-annotation

[adammw]

Yep, the idea is to fall back to the annotation if the first-class ingressClassName is not used..

[fpetkovski]

Ah I missed that part, then this makes sense to me 👍

/lgtm

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: adammw, fpetkovski

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