Chapter 8. Dynamic provisioning
8.1. 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 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.
8.2. Available dynamic provisioning plugins
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:
| Storage type | Provisioner plugin name | Notes |
|---|---|---|
| Red Hat OpenStack Platform (RHOSP) Cinder |
| |
| RHOSP Manila Container Storage Interface (CSI) |
| 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) |
|
For dynamic provisioning when using multiple clusters in different zones, tag each node with |
| Azure Disk |
| |
| Azure File |
|
The |
| GCE Persistent Disk (gcePD) |
| 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. |
|
|
Any chosen provisioner plugin also requires configuration for the relevant cloud, host, or third-party provider as per the relevant documentation.
8.3. 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 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.
8.3.1. 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 plugin to plug-iin.
8.3.2. 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
...8.3.3. RHOSP Cinder object definition
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
fsTypefield of dynamically provisioned persistent volumes and the file system is created when the volume is mounted for the first time. The default value isext4.
8.3.4. RHOSP Manila Container Storage Interface (CSI) object definition
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.
8.3.5. 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 isgp3. 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
trueorfalse. - 5
- Optional: The full ARN of the key to use when encrypting the volume. If none is supplied, but
encyptedis set totrue, 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
fsTypefield of dynamically provisioned persistent volumes and the file system is created when the volume is mounted for the first time. The default value isext4.
8.3.6. Azure Disk object definition
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
WaitForFirstConsumeris 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, andDedicated.ImportantRed Hat only supports the use of
kind: Managedin the storage class.With
SharedandDedicated, 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 withSharedorDedicatedcannot be attached to OpenShift Container Platform nodes. - 4
- Azure storage account SKU tier. Default is empty. Note that Premium VMs can attach both
Standard_LRSandPremium_LRSdisks, Standard VMs can only attachStandard_LRSdisks, Managed VMs can only attach managed disks, and unmanaged VMs can only attach unmanaged disks.-
If
kindis set toShared, Azure creates all unmanaged disks in a few shared storage accounts in the same resource group as the cluster. -
If
kindis set toManaged, Azure creates new managed disks. If
kindis set toDedicatedand astorageAccountis 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.
-
If
kindis set toDedicatedand astorageAccountis not specified, Azure creates a new dedicated storage account for the new unmanaged disk in the same resource group as the cluster.
-
If
8.3.7. Azure File object definition
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
Define a
ClusterRoleobject 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.
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
Create the Azure File
StorageClassobject: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 theStandard_LRSSKU. - 4
- Name of the Azure storage account. If a storage account is provided, then
skuNameandlocationare 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 definedskuNameandlocation.
8.3.7.1. Considerations when using Azure File
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
8.3.8. GCE PersistentDisk (gcePD) object definition
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
8.3.9. VMware vSphere object definition
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,zeroedthickandeagerzeroedthickare all valid disk formats. See vSphere docs for additional details regarding the disk format types. The default value isthin.
8.4. Changing the default storage class
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
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.
Change the value of the
storageclass.kubernetes.io/is-default-classannotation tofalsefor the default storage class:$ oc patch storageclass gp3 -p '{"metadata": {"annotations": {"storageclass.kubernetes.io/is-default-class": "false"}}}'Make another storage class the default by setting the
storageclass.kubernetes.io/is-default-classannotation totrue:$ oc patch storageclass standard -p '{"metadata": {"annotations": {"storageclass.kubernetes.io/is-default-class": "true"}}}'Verify the changes:
$ oc get storageclass
Example output
NAME TYPE gp3 kubernetes.io/aws-ebs standard (default) kubernetes.io/aws-ebs