placeholder PR for VAC beta
Matthew Cary
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layout: blog
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title: "Kubernetes 1.31: VolumeAttributesClass for Volume Modification Beta"
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date: 2024-08-15
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slug: kubernetes-1-31-volume-attributes-class
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author: >
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Sunny Song (Google)
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Matthew Cary (Google)
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---
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Volumes in Kubernetes have been described by two attributes: their storage class, and
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their capacity. The storage class is an immutable property of the volume, while the
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capacity can be changed dynamically with [volume
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resize](https://kubernetes.io/docs/concepts/storage/persistent-volumes/#expanding-persistent-volumes-claims).
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This complicates vertical scaling of workloads with volumes. While cloud providers and
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storage vendors often offer volumes which allow specifying IO quality of service
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(Performance) parameters like IOPS or throughput and tuning them as workloads operate,
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Kubernetes has no API which allows changing them.
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We are pleased to announce that the [VolumeAttributesClass
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KEP](https://github.com/kubernetes/enhancements/blob/master/keps/sig-storage/3751-volume-attributes-class/README.md),
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alpha since Kubernetes 1.29, will be beta in 1.31. This provides a generic,
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Kubernetes-native API for modifying volume parameters like provisioned IO.
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Like all new volume features in Kubernetes, this API is implemented via the [container
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storage interface (CSI)](https://kubernetes-csi.github.io/docs/). In addition to the
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VolumeAttributesClass feature gate, your provisioner-specific CSI driver must support the
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new ModifyVolume API which is the CSI side of this feature.
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See the [full
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documentation](https://kubernetes.io/docs/concepts/storage/volume-attributes-classes/)
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for all details. Here we show the common workflow.
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### Dynamically modifying volume attributes.
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A `VolumeAttributesClass` is a cluster-scoped resource that specifies provisioner-specific
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attributes. These are created by the cluster administrator in the same way as storage
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classes. For example, a series of gold, silver and bronze volume attribute classes can be
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created for volumes with greater or lessor amounts of provisioned IO.
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```yaml
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apiVersion: storage.k8s.io/v1alpha1
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kind: VolumeAttributesClass
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metadata:
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name: silver
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driverName: your-csi-driver
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parameters:
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provisioned-iops: "500"
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provisioned-throughput: "50MiB/s"
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---
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apiVersion: storage.k8s.io/v1alpha1
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kind: VolumeAttributesClass
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metadata:
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name: gold
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driverName: your-csi-driver
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parameters:
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provisioned-iops: "10000"
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provisioned-throughput: "500MiB/s"
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```
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An attribute class is added to a PVC in much the same way as a storage class.
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```yaml
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apiVersion: v1
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kind: PersistentVolumeClaim
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metadata:
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name: test-pv-claim
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spec:
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storageClassName: any-storage-class
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volumeAttributesClassName: silver
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accessModes:
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- ReadWriteOnce
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resources:
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requests:
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storage: 64Gi
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```
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Unlike a storage class, the volume attributes class can be changed:
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```
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kubectl patch pvc test-pv-claim -p '{"spec": "volumeAttributesClassName": "gold"}'
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```
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Kubernetes will work with the CSI driver to update the attributes of the
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volume. The status of the PVC will track the current and desired attributes
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class. The PV resource will also be updated with the new volume attributes class
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which will be set to the currently active attributes of the PV.
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### Limitations with the beta
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As a beta feature, there are still some features which are planned for GA but not yet
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present. The largest is quota support, see the
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[KEP](https://github.com/kubernetes/enhancements/blob/master/keps/sig-storage/3751-volume-attributes-class/README.md)
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and discussion in
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[sig-storage](https://github.com/kubernetes/community/tree/master/sig-storage) for details.
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See the [Kubernetes CSI driver
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list](https://kubernetes-csi.github.io/docs/drivers.html) for up-to-date
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information of support for this feature in CSI drivers.
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