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Chapter 4. Dynamic provisioning

4.1. About dynamic provisioning

The StorageClass resource object describes and classifies storage that can be requested, as well as provides a means for passing parameters for dynamically provisioned storage on demand. StorageClass objects can also serve as a management mechanism for controlling different levels of storage and access to the storage. Cluster Administrators (cluster-admin) or Storage Administrators (storage-admin) define and create the StorageClass objects that users can request without needing any intimate knowledge about the underlying storage volume sources.

The OpenShift Container Platform persistent volume framework enables this functionality and allows administrators to provision a cluster with persistent storage. The framework also gives users a way to request those resources without having any knowledge of the underlying infrastructure.

Many storage types are available for use as persistent volumes in OpenShift Container Platform. While all of them can be statically provisioned by an administrator, some types of storage are created dynamically using the built-in provider and plug-in APIs.

4.2. Available dynamic provisioning plug-ins

OpenShift Container Platform provides the following provisioner plug-ins, which have generic implementations for dynamic provisioning that use the cluster’s configured provider’s API to create new storage resources:

Storage type	Provisioner plug-in name	Notes
AWS Elastic Block Store (EBS)	`kubernetes.io/aws-ebs`	For dynamic provisioning when using multiple clusters in different zones, tag each node with `Key=kubernetes.io/cluster/<cluster_name>,Value=<cluster_id>` where `<cluster_name>` and `<cluster_id>` are unique per cluster.
VMware vSphere	`kubernetes.io/vsphere-volume`

Important

Any chosen provisioner plug-in also requires configuration for the relevant cloud, host, or third-party provider as per the relevant documentation.

4.3. Defining a StorageClass

StorageClass objects are currently a globally scoped object and must be created by cluster-admin or storage-admin users.

Important

The ClusterStorageOperator may install a default StorageClass depending on the platform in use. This StorageClass is owned and controlled by the operator. It cannot be deleted or modified beyond defining annotations and labels. If different behavior is desired, you must define a custom StorageClass.

The following sections describe the basic object definition for a StorageClass and specific examples for each of the supported plug-in types.

4.3.1. Basic StorageClass object definition

The following resource shows the parameters and default values that you use to configure a StorageClass. This example uses the AWS ElasticBlockStore (EBS) object definition.

Sample StorageClass definition

kind: StorageClass 1
apiVersion: storage.k8s.io/v1 2
metadata:
  name: gp2 3
  annotations: 4
    storageclass.kubernetes.io/is-default-class: 'true'
    ...
provisioner: kubernetes.io/aws-ebs 5
parameters: 6
  type: gp2
...

1: (required) The API object type.
2: (required) The current apiVersion.
3: (required) The name of the StorageClass.
4: (optional) Annotations for the StorageClass
5: (required) The type of provisioner associated with this storage class.
6: (optional) The parameters required for the specific provisioner, this will change from plug-in to plug-in.

4.3.2. StorageClass annotations

To set a StorageClass as the cluster-wide default, add the following annotation to your StorageClass’s metadata:

storageclass.kubernetes.io/is-default-class: "true"

For example:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  annotations:
    storageclass.kubernetes.io/is-default-class: "true"
...

This enables any Persistent Volume Claim (PVC) that does not specify a specific volume to automatically be provisioned through the default StorageClass.

Note

The beta annotation storageclass.beta.kubernetes.io/is-default-class is still working; however, it will be removed in a future release.

To set a StorageClass description, add the following annotation to your StorageClass’s metadata:

kubernetes.io/description: My StorageClass Description

For example:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  annotations:
    kubernetes.io/description: My StorageClass Description
...

4.3.3. AWS Elastic Block Store (EBS) object definition

aws-ebs-storageclass.yaml

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: slow
provisioner: kubernetes.io/aws-ebs
parameters:
  type: io1 1
  iopsPerGB: "10" 2
  encrypted: "true" 3
  kmsKeyId: keyvalue 4
  fsType: ext4 5

1: (required) Select from io1, gp2, sc1, st1. The default is gp2. See the AWS documentation for valid Amazon Resource Name (ARN) values.
2: (optional) Only for io1 volumes. I/O operations per second per GiB. The AWS volume plug-in multiplies this with the size of the requested volume to compute IOPS of the volume. The value cap is 20,000 IOPS, which is the maximum supported by AWS. See the AWS documentation for further details.
3: (optional) Denotes whether to encrypt the EBS volume. Valid values are true or false.
4: (optional) The full ARN of the key to use when encrypting the volume. If none is supplied, but encypted is set to true, then AWS generates a key. See the AWS documentation for a valid ARN value.
5: (optional) File system that is created on dynamically provisioned volumes. This value is copied to the fsType field of dynamically provisioned persistent volumes and the file system is created when the volume is mounted for the first time. The default value is ext4.

4.3.4. VMware vSphere object definition

vsphere-storageclass.yaml

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: slow
provisioner: kubernetes.io/vsphere-volume 1
parameters:
  diskformat: thin 2

1: For more information about using VMware vSphere with OpenShift Container Platform, see the VMware vSphere documentation.
2: diskformat: thin, zeroedthick and eagerzeroedthick are all valid disk formats. See vSphere docs for additional details regarding the disk format types. The default value is thin.

4.4. Changing the default StorageClass

If you are using AWS, use the following process to change the default StorageClass. This process assumes you have two StorageClasses defined, gp2 and standard, and you want to change the default StorageClass from gp2 to standard.

List the StorageClass:

$ oc get storageclass

NAME                 TYPE
gp2 (default)        kubernetes.io/aws-ebs 1
standard             kubernetes.io/aws-ebs

1: (default) denotes the default StorageClass.

Change the value of the annotation storageclass.kubernetes.io/is-default-class to false for the default StorageClass:

$ oc patch storageclass gp2 -p '{"metadata": {"annotations": {"storageclass.kubernetes.io/is-default-class": "false"}}}'

Make another StorageClass the default by adding or modifying the annotation as storageclass.kubernetes.io/is-default-class=true.
```
$ oc patch storageclass standard -p '{"metadata": {"annotations": {"storageclass.kubernetes.io/is-default-class": "true"}}}'
```

Verify the changes:

$ oc get storageclass

NAME                 TYPE
gp2                  kubernetes.io/aws-ebs
standard (default)   kubernetes.io/aws-ebs