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Chapter 9. Dynamic provisioning

9.1. About dynamic provisioning
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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 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 plugin APIs.

9.2. Available dynamic provisioning plugins
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OpenShift Container Platform 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:

Expand
Storage typeProvisioner plugin nameNotes

Red Hat OpenStack Platform (RHOSP) Cinder 

kubernetes.io/cinder

 

RHOSP Manila Container Storage Interface (CSI) 

manila.csi.openstack.org

Once installed, the OpenStack Manila CSI Driver Operator and ManilaDriver automatically create the required storage classes for all available Manila share types needed for dynamic provisioning.

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.

Azure Disk 

kubernetes.io/azure-disk

 

Azure File 

kubernetes.io/azure-file

The 

persistent-volume-binder
service account requires permissions to create and get secrets to store the Azure storage account and keys.

GCE Persistent Disk (gcePD) 

kubernetes.io/gce-pd

In multi-zone configurations, it is advisable to run one OpenShift Container Platform cluster per GCE project to avoid PVs from being created in zones where no node in the current cluster exists.

VMware vSphere 

kubernetes.io/vsphere-volume

 
Important

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

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

Important

The Cluster Storage Operator might install a default storage class depending on the platform in use. 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.

9.3.1. Basic StorageClass object definition
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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.

9.3.2. Storage class annotations
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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.

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 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
...

9.3.3. RHOSP Cinder object definition
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cinder-storageclass.yaml

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: <storage-class-name>
1 

provisioner: kubernetes.io/cinder
parameters:
  type: fast
2 

  availability: nova
3 

  fsType: ext4
4

1
Name of the storage class. The persistent volume claim uses this storage class for provisioning the associated persistent volumes.
2
Volume type created in Cinder. Default is empty.
3
Availability Zone. If not specified, volumes are generally round-robined across all active zones where the OpenShift Container Platform cluster has a node.
4
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.

9.3.4. RHOSP Manila Container Storage Interface (CSI) object definition
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Once installed, the OpenStack Manila CSI Driver Operator and ManilaDriver automatically create the required storage classes for all available Manila share types needed for dynamic provisioning.

9.3.5. AWS Elastic Block Store (EBS) object definition
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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.

9.3.6. Azure Disk object definition
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azure-advanced-disk-storageclass.yaml

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: <storage-class-name>
1 

provisioner: kubernetes.io/azure-disk
volumeBindingMode: WaitForFirstConsumer
2 

allowVolumeExpansion: true
parameters:
  kind: Managed
3 

  storageaccounttype: Premium_LRS
4 

reclaimPolicy: Delete

1
Name of the storage class. The persistent volume claim uses this storage class for provisioning the associated persistent volumes.
2
Using WaitForFirstConsumer is strongly recommended. This provisions the volume while allowing enough storage to schedule the pod on a free worker node from an available zone.
3
Possible values are Shared (default), Managed, and Dedicated.
Important

Red Hat only supports the use of 

kind: Managed
in the storage class.

With 

Shared
and 
Dedicated
, Azure creates unmanaged disks, while OpenShift Container Platform creates a managed disk for machine OS (root) disks. But because Azure Disk does not allow the use of both managed and unmanaged disks on a node, unmanaged disks created with 
Shared
or 
Dedicated
cannot be attached to OpenShift Container Platform nodes.

4
Azure storage account SKU tier. Default is empty. Note that Premium VMs can attach both Standard_LRS and Premium_LRS disks, Standard VMs can only attach Standard_LRS disks, Managed VMs can only attach managed disks, and unmanaged VMs can only attach unmanaged disks.
  1. If 
    kind
    is set to 
    Shared
    , Azure creates all unmanaged disks in a few shared storage accounts in the same resource group as the cluster.
  2. If 
    kind
    is set to 
    Managed
    , Azure creates new managed disks.

  3. If 

    kind
    is set to 
    Dedicated
    and a 
    storageAccount
    is specified, Azure uses the specified storage account for the new unmanaged disk in the same resource group as the cluster. For this to work:

    • The specified storage account must be in the same region.
    • Azure Cloud Provider must have write access to the storage account.
  4. If 
    kind
    is set to 
    Dedicated
    and a 
    storageAccount
    is not specified, Azure creates a new dedicated storage account for the new unmanaged disk in the same resource group as the cluster.

9.3.7. Azure File object definition
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The Azure File storage class uses secrets to store the Azure storage account name and the storage account key that are required to create an Azure Files share. These permissions are created as part of the following procedure.

Procedure

  1. Define a 

    ClusterRole
    object that allows access to create and view secrets: 

    apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
#  name: system:azure-cloud-provider
  name: <persistent-volume-binder-role>
    1 
    
rules:
- apiGroups: ['']
  resources: ['secrets']
  verbs:     ['get','create']
    1
    The name of the cluster role to view and create secrets.

  2. Add the cluster role to the service account: 

    $ oc adm policy add-cluster-role-to-user <persistent-volume-binder-role> system:serviceaccount:kube-system:persistent-volume-binder

  3. Create the Azure File 

    StorageClass
    object: 

    kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: <azure-file>
    1 
    
provisioner: kubernetes.io/azure-file
parameters:
  location: eastus
    2 
    
  skuName: Standard_LRS
    3 
    
  storageAccount: <storage-account>
    4 
    
reclaimPolicy: Delete
volumeBindingMode: Immediate
    1
    Name of the storage class. The persistent volume claim uses this storage class for provisioning the associated persistent volumes.
    2
    Location of the Azure storage account, such as eastus. Default is empty, meaning that a new Azure storage account will be created in the OpenShift Container Platform cluster’s location.
    3
    SKU tier of the Azure storage account, such as Standard_LRS. Default is empty, meaning that a new Azure storage account will be created with the Standard_LRS SKU.
    4
    Name of the Azure storage account. If a storage account is provided, then skuName and location are ignored. If no storage account is provided, then the storage class searches for any storage account that is associated with the resource group for any accounts that match the defined skuName and location.

9.3.7.1. Considerations when using Azure File
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The following file system features are not supported by the default Azure File storage class:

  • Symlinks
  • Hard links
  • Extended attributes
  • Sparse files
  • Named pipes

Additionally, the owner user identifier (UID) of the Azure File mounted directory is different from the process UID of the container. The 

uid
mount option can be specified in the 
StorageClass
object to define a specific user identifier to use for the mounted directory.

The following 

StorageClass
object demonstrates modifying the user and group identifier, along with enabling symlinks for the mounted directory. 

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: azure-file
mountOptions:
  - uid=1500
1 

  - gid=1500
2 

  - mfsymlinks
3 

provisioner: kubernetes.io/azure-file
parameters:
  location: eastus
  skuName: Standard_LRS
reclaimPolicy: Delete
volumeBindingMode: Immediate
1
Specifies the user identifier to use for the mounted directory.
2
Specifies the group identifier to use for the mounted directory.
3
Enables symlinks.

9.3.8. GCE PersistentDisk (gcePD) object definition
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gce-pd-storageclass.yaml

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: <storage-class-name>
1 

provisioner: kubernetes.io/gce-pd
parameters:
  type: pd-standard
2 

  replication-type: none
volumeBindingMode: WaitForFirstConsumer
allowVolumeExpansion: true
reclaimPolicy: Delete

1
Name of the storage class. The persistent volume claim uses this storage class for provisioning the associated persistent volumes.
2
Select either pd-standard or pd-ssd. The default is pd-standard.

9.3.9. VMware vSphere object definition
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vsphere-storageclass.yaml

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: <storage-class-name>
1 

provisioner: kubernetes.io/vsphere-volume
2 

parameters:
  diskformat: thin
3

1
Name of the storage class. The persistent volume claim uses this storage class for provisioning the associated persistent volumes.
2
For more information about using VMware vSphere with OpenShift Container Platform, see the VMware vSphere documentation.
3
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.

9.4. Changing the default storage class
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Use this procedure to change the default storage class. For example, you have two defined storage classes, 

gp3
and 
standard
, and you want to change the default storage class from 
gp3
to 
standard
.

Procedure

  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) denotes the default storage class.

  2. Change the value of the 

    storageclass.kubernetes.io/is-default-class
    annotation to 
    false
    for the default storage class: 

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

  3. Make another storage class the default by setting the 

    storageclass.kubernetes.io/is-default-class
    annotation to 
    true
    : 

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

  4. Verify the changes: 

    $ oc get storageclass

    Example output

    NAME                 TYPE
gp3                  kubernetes.io/aws-ebs
standard (default)   kubernetes.io/aws-ebs

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