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Dynamic provisioning

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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 detailed knowledge about the underlying storage volume sources.

The Red Hat OpenShift Service on AWS 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 Red Hat OpenShift Service on AWS. While all of them can be statically provisioned by an administrator, some types of storage are created dynamically using the built-in provider and plugin APIs.

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Available dynamic provisioning plugins

Red Hat OpenShift Service on AWS provides the following provisioner plugins, which have generic implementations for dynamic provisioning that use the cluster’s configured provider’s API to create new storage resources:

Storage type Provisioner plugin name Notes

Amazon Elastic Block Store (Amazon 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.

Any chosen provisioner plugin also requires configuration for the relevant cloud, host, or third-party provider as per the relevant documentation.
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Defining a storage class

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

The Cluster Storage Operator installs a default storage class. This storage class 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 storage class.

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

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Basic StorageClass object definition

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

Sample StorageClass definition
kind: StorageClass (1)
apiVersion: storage.k8s.io/v1 (2)
metadata:
  name: <storage-class-name> (3)
  annotations: (4)
    storageclass.kubernetes.io/is-default-class: 'true'
    ...
provisioner: kubernetes.io/aws-ebs (5)
parameters: (6)
  type: gp3
...
1 (required) The API object type.
2 (required) The current apiVersion.
3 (required) The name of the storage class.
4 (optional) Annotations for the storage class.
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.
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Storage class annotations

To set a storage class as the cluster-wide default, add the following annotation to your storage class 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 storage class to automatically be provisioned through the default storage class. However, your cluster can have more than one storage class, but only one of them can be the default storage class.

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 storage class description, add the following annotation to your storage class metadata:

kubernetes.io/description: My Storage Class Description

For example:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  annotations:
    kubernetes.io/description: My Storage Class Description
...
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AWS Elastic Block Store (EBS) object definition

aws-ebs-storageclass.yaml
kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: <storage-class-name> (1)
provisioner: kubernetes.io/aws-ebs
parameters:
  type: io1 (2)
  iopsPerGB: "10" (3)
  encrypted: "true" (4)
  kmsKeyId: keyvalue (5)
  fsType: ext4 (6)
1 (required) Name of the storage class. The persistent volume claim uses this storage class for provisioning the associated persistent volumes.
2 (required) Select from io1, gp3, sc1, st1. The default is gp3. See the AWS documentation for valid Amazon Resource Name (ARN) values.
3 Optional: Only for io1 volumes. I/O operations per second per GiB. The AWS volume plugin 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.
4 Optional: Denotes whether to encrypt the EBS volume. Valid values are true or false.
5 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.
6 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.
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Changing the default storage class

Use the following procedure to change the default storage class.

For example, if you have two defined storage classes, gp3 and standard, and you want to change the default storage class from gp3 to standard.

Prerequisites

  • Access to the cluster with cluster-admin privileges.

Procedure

To change the default storage class:

  1. List the storage classes:

    $ oc get storageclass
    Example output
    NAME                 TYPE
gp3 (default)        kubernetes.io/aws-ebs (1)
standard             kubernetes.io/aws-ebs
    1 (default) indicates the default storage class.

  2. Make the desired storage class the default.

    For the desired storage class, set the storageclass.kubernetes.io/is-default-class annotation to true by running the following command:

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

    You can have multiple default storage classes for a short time. However, you should ensure that only one default storage class exists eventually.

    With multiple default storage classes present, any persistent volume claim (PVC) requesting the default storage class (pvc.spec.storageClassName=nil) gets the most recently created default storage class, regardless of the default status of that storage class, and the administrator receives an alert in the alerts dashboard that there are multiple default storage classes, MultipleDefaultStorageClasses.

  3. Remove the default storage class setting from the old default storage class.

    For the old default storage class, change the value of the storageclass.kubernetes.io/is-default-class annotation to false by running the following command:

    $ oc patch storageclass gp3 -p '{"metadata": {"annotations": {"storageclass.kubernetes.io/is-default-class": "false"}}}'

  4. Verify the changes:

    $ oc get storageclass
    Example output
    NAME                 TYPE
gp3                  kubernetes.io/aws-ebs
standard (default)   kubernetes.io/aws-ebs