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Persistent Storage Using AWS Elastic Block Store

OpenShift Container Platform supports AWS Elastic Block Store volumes (EBS). You can provision your OpenShift Container Platform cluster with persistent storage using AWS EC2. Some familiarity with Kubernetes and AWS is assumed.

The Kubernetes persistent volume framework allows administrators to provision a cluster with persistent storage and gives users a way to request those resources without having any knowledge of the underlying infrastructure. AWS Elastic Block Store volumes can be provisioned dynamically. Persistent volumes are not bound to a single project or namespace; they can be shared across the OpenShift Container Platform cluster. Persistent volume claims are specific to a project or namespace and can be requested by users.

High-availability of storage in the infrastructure is left to the underlying storage provider.
Additional References

Creating the EBS Storage Class

StorageClasses are used to differentiate and delineate storage levels and usages. By defining a storage class, users can obtain dynamically provisioned persistent volumes.

Procedure

  1. In the OpenShift Container Platform console, click Storage → Storage Classes.

  2. In the storage class overview, click Create Storage Class.

  3. Define the desired options on the page that appears.

    1. Enter a name to reference the storage class.

    2. Enter an optional description.

    3. Select the reclaim policy.

    4. Select kubernetes.io/aws-ebs from the drop down list.

    5. Enter additional parameters for the storage class as desired.

  4. Click Create to create the storage class.

Creating the Persistent Volume Claim

Prerequisites

Storage must exist in the underlying infrastructure before it can be mounted as a volume in OpenShift Container Platform.

Procedure

  1. In the OpenShift Container Platform console, click Storage → Persistent Volume Claims.

  2. In the persistent volume claims overview, click Create Persistent Volume Claim.

  3. Define the desired options on the page that appears.

    1. Select the storage class created previously from the drop-down menu.

    2. Enter a unique name for the storage claim.

    3. Select the access mode. This determines the read and write access for the created storage claim.

    4. Define the size of the storage claim.

  4. Click Create to create the persistent volume claim and generate a persistent volume.

Volume Format

Before OpenShift Container Platform mounts the volume and passes it to a container, it checks that it contains a file system as specified by the fsType parameter in the persistent volume definition. If the device is not formatted with the file system, all data from the device is erased and the device is automatically formatted with the given file system.

This allows using unformatted AWS volumes as persistent volumes, because OpenShift Container Platform formats them before the first use.

Maximum Number of EBS Volumes on a Node

By default, OpenShift Container Platform supports a maximum of 39 EBS volumes attached to one node. This limit is consistent with the AWS volume limits.

OpenShift Container Platform can be configured to have a higher limit by setting the environment variable KUBE_MAX_PD_VOLS. However, AWS requires a particular naming scheme (AWS Device Naming) for attached devices, which only supports a maximum of 52 volumes. This limits the number of volumes that can be attached to a node via OpenShift Container Platform to 52.