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Persistent storage using hostPath

A hostPath volume in an OpenShift Container Platform cluster mounts a file or directory from the host node’s filesystem into your pod. Most pods will not need a hostPath volume, but it does offer a quick option for testing should an application require it.

The cluster administrator must configure pods to run as privileged. This grants access to pods in the same node.

Overview

OpenShift Container Platform supports hostPath mounting for development and testing on a single-node cluster.

In a production cluster, you would not use hostPath. Instead, a cluster administrator would provision a network resource, such as a GCE Persistent Disk volume, an NFS share, or an Amazon EBS volume. Network resources support the use of storage classes to set up dynamic provisioning.

A hostPath volume must be provisioned statically.

Statically provisioning hostPath volumes

A pod that uses a hostPath volume must be referenced by manual (static) provisioning.

Procedure

  1. Define the persistent volume (PV). Create a file, pv.yaml, with the PersistentVolume object definition:

      apiVersion: v1
  kind: PersistentVolume
  metadata:
    name: task-pv-volume (1)
    labels:
      type: local
  spec:
    storageClassName: manual (2)
    capacity:
      storage: 5Gi
    accessModes:
      - ReadWriteOnce (3)
    persistentVolumeReclaimPolicy: Retain
    hostPath:
      path: "/mnt/data" (4)
    1 The name of the volume. This name is how it is identified by persistent volume claims or pods.
    2 Used to bind persistent volume claim requests to this persistent volume.
    3 The volume can be mounted as read-write by a single node.
    4 The configuration file specifies that the volume is at /mnt/data on the cluster’s node.

  2. Create the PV from the file:

    $ oc create -f pv.yaml

  3. Define the persistent volume claim (PVC). Create a file, pvc.yaml, with the PersistentVolumeClaim object definition:

    apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: task-pvc-volume
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
  storageClassName: manual

  4. Create the PVC from the file:

    $ oc create -f pvc.yaml

Mounting the hostPath share in a privileged pod

After the persistent volume claim has been created, it can be used inside by an application. The following example demonstrates mounting this share inside of a pod.

Prerequisites

  • A persistent volume claim exists that is mapped to the underlying hostPath share.

Procedure

  • Create a privileged pod that mounts the existing persistent volume claim:

    apiVersion: v1
kind: Pod
metadata:
  name: pod-name (1)
spec:
  containers:
    ...
    securityContext:
      privileged: true (2)
    volumeMounts:
    - mountPath: /data (3)
      name: hostpath-privileged
  ...
  securityContext: {}
  volumes:
    - name: hostpath-privileged
      persistentVolumeClaim:
        claimName: task-pvc-volume (4)
    1 The name of the pod.
    2 The pod must run as privileged to access the node’s storage.
    3 The path to mount the hostPath share inside the privileged pod.
    4 The name of the PersistentVolumeClaim object that has been previously created.