Volume Attributes Classes

This page assumes that you are familiar with StorageClasses, volumes and PersistentVolumes in Kubernetes.

A VolumeAttributesClass provides a way for administrators to describe the mutable "classes" of storage they offer. Different classes might map to different quality-of-service levels. Kubernetes itself is unopinionated about what these classes represent.

This is an alpha feature and disabled by default.

If you want to test the feature whilst it's alpha, you need to enable the VolumeAttributesClass feature gate for the kube-controller-manager and the kube-apiserver. You use the --feature-gates command line argument:

--feature-gates="...,VolumeAttributesClass=true"

You can also only use VolumeAttributesClasses with storage backed by Container Storage Interface, and only where the relevant CSI driver implements the ModifyVolume API.

The VolumeAttributesClass API

Each VolumeAttributesClass contains the driverName and parameters, which are used when a PersistentVolume (PV) belonging to the class needs to be dynamically provisioned or modified.

The name of a VolumeAttributesClass object is significant and is how users can request a particular class. Administrators set the name and other parameters of a class when first creating VolumeAttributesClass objects. While the name of a VolumeAttributesClass object in a PersistentVolumeClaim is mutable, the parameters in an existing class are immutable.

apiVersion: storage.k8s.io/v1alpha1
kind: VolumeAttributesClass
metadata:
  name: silver
driverName: pd.csi.storage.gke.io
parameters:
  provisioned-iops: "3000"
  provisioned-throughput: "50" 

Provisioner

Each VolumeAttributesClass has a provisioner that determines what volume plugin is used for provisioning PVs. The field driverName must be specified.

The feature support for VolumeAttributesClass is implemented in kubernetes-csi/external-provisioner.

You are not restricted to specifying the kubernetes-csi/external-provisioner. You can also run and specify external provisioners, which are independent programs that follow a specification defined by Kubernetes. Authors of external provisioners have full discretion over where their code lives, how the provisioner is shipped, how it needs to be run, what volume plugin it uses, etc.

Resizer

Each VolumeAttributesClass has a resizer that determines what volume plugin is used for modifying PVs. The field driverName must be specified.

The modifying volume feature support for VolumeAttributesClass is implemented in kubernetes-csi/external-resizer.

For example, a existing PersistentVolumeClaim is using a VolumeAttributesClass named silver:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: test-pv-claim
spec:
  …
  volumeAttributesClassName: silver
  …

A new VolumeAttributesClass gold is available in the cluster:

apiVersion: storage.k8s.io/v1alpha1
kind: VolumeAttributesClass
metadata:
  name: gold
driverName: pd.csi.storage.gke.io
parameters:
  iops: "4000"
  throughput: "60"

The end user can update the PVC with the new VolumeAttributesClass gold and apply:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: test-pv-claim
spec:
  …
  volumeAttributesClassName: gold
  …

Parameters

VolumeAttributeClasses have parameters that describe volumes belonging to them. Different parameters may be accepted depending on the provisioner or the resizer. For example, the value 4000, for the parameter iops, and the parameter throughput are specific to GCE PD. When a parameter is omitted, the default is used at volume provisioning. If a user apply the PVC with a different VolumeAttributesClass with omitted parameters, the default value of the parameters may be used depends on the CSI driver implementation. Please refer to the related CSI driver documentation for more details.

There can be at most 512 parameters defined for a VolumeAttributesClass. The total length of the parameters object including its keys and values cannot exceed 256 KiB.