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Selector-Label Volume Binding

Overview

This guide provides the steps necessary to enable binding of persistent volume claims (PVCs) to persistent volumes (PVs) via selector and label attributes. By implementing selectors and labels, regular users are able to target provisioned storage by identifiers defined by a cluster administrator.

Motivation

In cases of statically provisioned storage, developers seeking persistent storage are required to know a handful identifying attributes of a PV in order to deploy and bind a PVC. This creates several problematic situations. Regular users might have to contact a cluster administrator to either deploy the PVC or provide the PV values. PV attributes alone do not convey the intended use of the storage volumes, nor do they provide methods by which volumes can be grouped.

Selector and label attributes can be used to abstract away PV details from the user while providing cluster administrators a way of identifying volumes by a descriptive and customizable tag. Through the selector-label method of binding, users are only required to know which labels are defined by the administrator.

The selector-label feature is currently only available for statically provisioned storage and is currently not implemented for storage provisioned dynamically.

Deployment

This section reviews how to define and deploy PVCs.

Prerequisites

  1. A running OKD 3.3+ cluster

  2. A volume provided by a supported storage provider

  3. A user with a cluster-admin role binding

Define the Persistent Volume and Claim

  1. As the cluser-admin user, define the PV. For this example, we will be using a GlusterFS volume. See the appropriate storage provider for your provider’s configuration.

    Example 1. Persistent Volume with Labels
    apiVersion: v1
kind: PersistentVolume
metadata:
  name: gluster-volume
  labels: (1)
    volume-type: ssd
    aws-availability-zone: us-east-1
spec:
  capacity:
    storage: 2Gi
  accessModes:
    - ReadWriteMany
  glusterfs:
    endpoints: glusterfs-cluster
    path: myVol1
    readOnly: false
  persistentVolumeReclaimPolicy: Recycle
    1 A PVC whose selectors match all of a PV’s labels will be bound, assuming a PV is available.

  2. Define the PVC:

    Example 2. Persistent Volume Claim with Selectors
    apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: gluster-claim
spec:
  accessModes:
  - ReadWriteMany
  resources:
     requests:
       storage: 1Gi
  selector: (1)
    matchLabels: (2)
      volume-type: ssd
      aws-availability-zone: us-east-1
    1 Begin selectors section.
    2 List all labels by which the user is requesting storage. Must match all labels of targeted PV.

Deploy the Persistent Volume and Claim

As the cluster-admin user, create the persistent volume:

Example 3. Create the Persistent Volume
# oc create -f gluster-pv.yaml
persistentVolume "gluster-volume" created

# oc get pv
NAME                     LABELS    CAPACITY     ACCESSMODES   STATUS      CLAIM     REASON    AGE
gluster-volume            map[]    2147483648   RWX           Available                       2s

Once the PV is created, any user whose selectors match all its labels can create their PVC.

Example 4. Create the Persistent Volume Claim
# oc create -f gluster-pvc.yaml
persistentVolumeClaim "gluster-claim" created
# oc get pvc
NAME          LABELS    STATUS    VOLUME
gluster-claim           Bound     gluster-volume