feat: Add local storage labels to kube_persistentvolume_info

[nabokihms]

Signed-off-by: m.nabokikh maksim.nabokikh@flant.com

What this PR does / why we need it:
Local volumes in Kubernetes differ from other volumes, e.g., they do not have the max cap as other persistent volumes. Instead, local PVs can consume all the available space on the disk. Thus, there should be a way to distinguish local PVs (and other rules to monitor them).

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)
Yes, it make local storage volumes metrics looks like kube_persistentvolume_info{local_path="/mnt/data", local_fs="ext4"}

[nabokihms]

Maybe it would be best to also add the host_path_ labels family, because these are also indicate local volumes.

[dgrisonnet]

At this point, I wonder if it was really a good idea to add all the FS types to the _info metric. It is growing an insane amount of labels with makes it kind of unreadable. Not that metrics themselves should be readable but metrics are easier to discover than labels. Considering the amount of possible volumes sources (https://pkg.go.dev/k8s.io/api/core/v1#PersistentVolumeSource), it might just be better to create one metric per source.

[nabokihms]

The idea to add specific labels to a dedicated metric seems more than ok to me.

Something like:

kube_persistentvolume_info{type="csi", persistentvolume="test-1"}
kube_persistentvolume_csi_info{persistentvolume="test-1", driver="ABC", volume_handle="csi-volume-handle"}
kube_persistentvolume_info{type="local", persistentvolume="test-2"}
kube_persistentvolume_local_info{persistentvolume="test-2", path="/mnt", fs="ext4"}

@dgrisonnet Does it seem ok to you? If so, I can dig to implement it more generic way.

[nabokihms]

I reverted table changes and add host path labels.

[dgrisonnet]

LGTM, thank you @nabokihms for the contribution :)

/lgtm
/approve

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[dgrisonnet]

Yeah your suggestion is pretty similar to what I had in mind, I'll start a github discussion around that topic.

[nabokihms]

@dgrisonnet I'd like to participate, if it is possible.
😄