Dynamic provisioning

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 plug-in APIs.

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

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.

AWS Elastic File System (EFS)

Dynamic provisioning is accomplished through the EFS provisioner Pod and not through a provisioner plug-in.

Azure Disk

kubernetes.io/azure-disk

Azure File

kubernetes.io/azure-file

The persistent-volume-binder ServiceAccount 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

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

Defining a StorageClass

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

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.

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.

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 StorageClass to automatically be provisioned through the default StorageClass.

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
...

RHOSP Cinder object definition

cinder-storageclass.yaml
kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: gold
provisioner: kubernetes.io/cinder
parameters:
  type: fast  (1)
  availability: nova (2)
  fsType: ext4 (3)
1 Volume type created in Cinder. Default is empty.
2 Availability Zone. If not specified, volumes are generally round-robined across all active zones where the OpenShift Container Platform cluster has a node.
3 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.

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.

Azure Disk object definition

azure-advanced-disk-storageclass.yaml
kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: slow
provisioner: kubernetes.io/azure-disk
parameters:
  storageAccount: azure_storage_account_name  (1)
  storageaccounttype: Standard_LRS  (2)
  kind: Dedicated  (3)
1 Azure storage account name. This must reside in the same resource group as the cluster. If a storage account is specified, the location is ignored. If a storage account is not specified, a new storage account gets created in the same resource group as the cluster. If you are specifying a storageAccount, the value for kind must be Dedicated.
2 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.
3 Possible values are Shared (default), Dedicated, and Managed.
  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 a 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.

Azure File object definition

The Azure File StorageClass 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 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 ClusterRole to view and create secrets.
  2. Add the ClusterRole to the ServiceAccount:

    $ oc adm policy add-cluster-role-to-user <persistent-volume-binder-role>
    Example output
     system:serviceaccount:kube-system:persistent-volume-binder
  3. Create the Azure File StorageClass:

    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 StorageClass. The PersistentVolumeClaim uses this StorageClass for provisioning the associated PersistentVolumes.
    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 StorageClass searches for any storage account that is associated with the resource group for any accounts that match the defined skuName and location.

Considerations when using Azure File

The following file system features are not supported by the default Azure File StorageClass:

  • 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 to define a specific user identifier to use for the mounted directory.

The following StorageClass 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.

GCE PersistentDisk (gcePD) object definition

gce-pd-storageclass.yaml
kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: slow
provisioner: kubernetes.io/gce-pd
parameters:
  type: pd-standard  (1)
  replication-type: none
1 Select either pd-standard or pd-ssd. The default is pd-ssd.

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.

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.

  1. List the StorageClass:

    $ oc get storageclass
    Example output
    NAME                 TYPE
    gp2 (default)        kubernetes.io/aws-ebs (1)
    standard             kubernetes.io/aws-ebs
    1 (default) denotes the default StorageClass.
  2. 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"}}}'
  3. 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"}}}'
  4. Verify the changes:

    $ oc get storageclass
    Example output
    NAME                 TYPE
    gp2                  kubernetes.io/aws-ebs
    standard (default)   kubernetes.io/aws-ebs

Optimizing storage

Optimizing storage helps to minimize storage use across all resources. By optimizing storage, administrators help ensure that existing storage resources are working in an efficient manner.

Available persistent storage options

Understand your persistent storage options so that you can optimize your OpenShift Container Platform environment.

Table 1. Available storage options
Storage type Description Examples

Block

  • Presented to the operating system (OS) as a block device

  • Suitable for applications that need full control of storage and operate at a low level on files bypassing the file system

  • Also referred to as a Storage Area Network (SAN)

  • Non-shareable, which means that only one client at a time can mount an endpoint of this type

AWS EBS and VMware vSphere support dynamic persistent volume (PV) provisioning natively in OpenShift Container Platform.

File

  • Presented to the OS as a file system export to be mounted

  • Also referred to as Network Attached Storage (NAS)

  • Concurrency, latency, file locking mechanisms, and other capabilities vary widely between protocols, implementations, vendors, and scales.

RHEL NFS, NetApp NFS [1], and Vendor NFS

Object

  • Accessible through a REST API endpoint

  • Configurable for use in the OpenShift Container Platform Registry

  • Applications must build their drivers into the application and/or container.

AWS S3

  1. NetApp NFS supports dynamic PV provisioning when using the Trident plug-in.

Currently, CNS is not supported in OpenShift Container Platform 4.6.

Recommended configurable storage technology

The following table summarizes the recommended and configurable storage technologies for the given OpenShift Container Platform cluster application.

Table 2. Recommended and configurable storage technology
Storage type ROX1 RWX2 Registry Scaled registry Metrics3 Logging Apps

Block

Yes4

No

Configurable

Not configurable

Recommended

Recommended

Recommended

File

Yes4

Yes

Configurable

Configurable

Configurable5

Configurable6

Recommended

Object

Yes

Yes

Recommended

Recommended

Not configurable

Not configurable

Not configurable7

1 ReadOnlyMany

2 ReadWriteMany

3 Prometheus is the underlying technology used for metrics.

4 This does not apply to physical disk, VM physical disk, VMDK, loopback over NFS, AWS EBS, and Azure Disk.

5 For metrics, using file storage with the ReadWriteMany (RWX) access mode is unreliable. If you use file storage, do not configure the RWX access mode on any persistent volume claims (PVCs) that are configured for use with metrics.

6 For logging, using any shared storage would be an anti-pattern. One volume per elasticsearch is required.

7 Object storage is not consumed through OpenShift Container Platform’s PVs or PVCs. Apps must integrate with the object storage REST API.

A scaled registry is an OpenShift Container Platform registry where two or more pod replicas are running.

Specific application storage recommendations

Testing shows issues with using the NFS server on Red Hat Enterprise Linux (RHEL) as storage backend for core services. This includes the OpenShift Container Registry and Quay, Prometheus for monitoring storage, and Elasticsearch for logging storage. Therefore, using RHEL NFS to back PVs used by core services is not recommended.

Other NFS implementations on the marketplace might not have these issues. Contact the individual NFS implementation vendor for more information on any testing that was possibly completed against these OpenShift Container Platform core components.

Registry

In a non-scaled/high-availability (HA) OpenShift Container Platform registry cluster deployment:

  • The storage technology does not have to support RWX access mode.

  • The storage technology must ensure read-after-write consistency.

  • The preferred storage technology is object storage followed by block storage.

  • File storage is not recommended for OpenShift Container Platform registry cluster deployment with production workloads.

Scaled registry

In a scaled/HA OpenShift Container Platform registry cluster deployment:

  • The storage technology must support RWX access mode and must ensure read-after-write consistency.

  • The preferred storage technology is object storage.

  • Amazon Simple Storage Service (Amazon S3), Google Cloud Storage (GCS), Microsoft Azure Blob Storage, and OpenStack Swift are supported.

  • Object storage should be S3 or Swift compliant.

  • File storage is not recommended for a scaled/HA OpenShift Container Platform registry cluster deployment with production workloads.

  • For non-cloud platforms, such as vSphere and bare metal installations, the only configurable technology is file storage.

  • Block storage is not configurable.

Metrics

In an OpenShift Container Platform hosted metrics cluster deployment:

  • The preferred storage technology is block storage.

  • Object storage is not configurable.

It is not recommended to use file storage for a hosted metrics cluster deployment with production workloads.

Logging

In an OpenShift Container Platform hosted logging cluster deployment:

  • The preferred storage technology is block storage.

  • File storage is not recommended for a scaled/HA OpenShift Container Platform registry cluster deployment with production workloads.

  • Object storage is not configurable.

Testing shows issues with using the NFS server on RHEL as storage backend for core services. This includes Elasticsearch for logging storage. Therefore, using RHEL NFS to back PVs used by core services is not recommended.

Other NFS implementations on the marketplace might not have these issues. Contact the individual NFS implementation vendor for more information on any testing that was possibly completed against these OpenShift Container Platform core components.

Applications

Application use cases vary from application to application, as described in the following examples:

  • Storage technologies that support dynamic PV provisioning have low mount time latencies, and are not tied to nodes to support a healthy cluster.

  • Application developers are responsible for knowing and understanding the storage requirements for their application, and how it works with the provided storage to ensure that issues do not occur when an application scales or interacts with the storage layer.

Other specific application storage recommendations

  • OpenShift Container Platform Internal etcd: For the best etcd reliability, the lowest consistent latency storage technology is preferable.

  • It is highly recommended that you use etcd with storage that handles serial writes (fsync) quickly, such as NVMe or SSD. Ceph, NFS, and spinning disks are not recommended.

  • Red Hat OpenStack Platform (RHOSP) Cinder: RHOSP Cinder tends to be adept in ROX access mode use cases.

  • Databases: Databases (RDBMSs, NoSQL DBs, etc.) tend to perform best with dedicated block storage.

Deploy Red Hat OpenShift Container Storage

Red Hat OpenShift Container Storage is a provider of agnostic persistent storage for OpenShift Container Platform supporting file, block, and object storage, either in-house or in hybrid clouds. As a Red Hat storage solution, Red Hat OpenShift Container Storage is completely integrated with OpenShift Container Platform for deployment, management, and monitoring.

If you are looking for Red Hat OpenShift Container Storage information about…​ See the following Red Hat OpenShift Container Storage documentation:

What’s new, known issues, notable bug fixes, and Technology Previews

OpenShift Container Storage 4.5 Release Notes

Supported workloads, layouts, hardware and software requirements, sizing and scaling recommendations

Planning your OpenShift Container Storage 4.5 deployment

Instructions on preparing to deploy when your environment is not directly connected to the internet

Preparing to deploy OpenShift Container Storage 4.5 in a disconnected environment

Instructions on deploying OpenShift Container Storage to use an external Red Hat Ceph Storage cluster

Deploying OpenShift Container Storage 4.5 in external mode

Instructions on deploying OpenShift Container Storage to local storage on bare metal infrastructure

Deploying OpenShift Container Storage 4.5 using bare metal infrastructure

Instructions on deploying OpenShift Container Storage on Red Hat OpenShift Container Platform VMWare vSphere clusters

Deploying OpenShift Container Storage 4.5 on VMWare vSphere

Instructions on deploying OpenShift Container Storage using Amazon Web Services for local or cloud storage

Deploying OpenShift Container Storage 4.5 using Amazon Web Services

Instructions on deploying and managing OpenShift Container Storage on existing Red Hat OpenShift Container Platform Google Cloud clusters

Deploying and managing OpenShift Container Storage 4.5 using Google Cloud

Instructions on deploying and managing OpenShift Container Storage on existing Red Hat OpenShift Container Platform Azure clusters

Deploying and managing OpenShift Container Storage 4.5 using Microsoft Azure

Managing a Red Hat OpenShift Container Storage 4.5 cluster

Managing OpenShift Container Storage 4.5

Monitoring a Red Hat OpenShift Container Storage 4.5 cluster

Monitoring Red Hat OpenShift Container Storage 4.5

Resolve issues encountered during operations

Troubleshooting OpenShift Container Storage 4.5

Migrating your OpenShift Container Platform cluster from version 3 to version 4

Migration