diff --git a/contributors/design-proposals/volume_stats_pvc_ref.md b/contributors/design-proposals/volume_stats_pvc_ref.md new file mode 100644 index 00000000000..1b2f599b914 --- /dev/null +++ b/contributors/design-proposals/volume_stats_pvc_ref.md @@ -0,0 +1,57 @@ +# Add PVC reference in Volume Stats + +## Background +Pod volume stats tracked by kubelet do not currently include any information about the PVC (if the pod volume was referenced via a PVC) + +This prevents exposing (and querying) volume metrics labeled by PVC name which is preferable for users, given that PVC is a top-level API object. + +## Proposal + +Modify ```VolumeStats``` tracked in Kubelet and populate with PVC info: + +``` +// VolumeStats contains data about Volume filesystem usage. +type VolumeStats struct { + // Embedded FsStats + FsStats + // Name is the name given to the Volume + // +optional + Name string `json:"name,omitempty"` ++ // PVCRef is a reference to the measured PVC. ++ // +optional ++ PVCRef PVCReference `json:"pvcRef"` +} + ++// PVCReference contains enough information to describe the referenced PVC. ++type PVCReference struct { ++ Name string `json:"name"` ++ Namespace string `json:"namespace"` ++} +``` + +## Implementation +2 options are described below. Option 1 supports current requirements/requested use cases. Option 2 supports an additional use case that was being discussed and is called out for completeness/discussion/feedback. + +### Option 1 +- Modify ```kubelet::server::stats::calcAndStoreStats()``` + - If the pod volume is referenced via a PVC, populate ```PVCRef``` in VolumeStats using the Pod spec + + - The Pod spec is already available in this method, so the changes are contained to this function. + +- The limitation of this approach is that we're limited to reporting only what is available in the pod spec (Pod namespace and PVC claimname) + +### Option 2 +- Modify the ```volumemanager::GetMountedVolumesForPod()``` (or add a new function) to return additional volume information from the actual/desired state-of-world caches + - Use this to populate PVCRef in VolumeStats + +- This allows us to get information not available in the Pod spec such as the PV name/UID which can be used to label metrics - enables exposing/querying volume metrics by PV name +- It's unclear whether this is a use case we need to/should support: + * Volume metrics are only refreshed for mounted volumes which implies a bound/available PVC + * We expect most user-storage interactions to be via the PVC +- Admins monitoring PVs (and not PVC's) so that they know when their users are running out of space or are over-provisioning would be a use case supporting adding PV information to + metrics + + + + +