Managing Volumes

Overview

Containers are not persistent by default; on restart, their contents are cleared. Volumes are mounted file systems available to pods and their containers which may be backed by a number of host-local or network attached storage endpoints.

To ensure that the file system on the volume contains no errors and, if errors are present, to repair them when possible, OKD invokes the fsck utility prior to the mount utility. This occurs when either adding a volume or updating an existing volume.

The simplest volume type is emptyDir, which is a temporary directory on a single machine. Administrators may also allow you to request a persistent volume that is automatically attached to your pods.

You can use the CLI command oc set volume to add, update, or remove volumes and volume mounts for any object that has a pod template like replication controllers or deployment configurations. You can also list volumes in pods or any object that has a pod template.

General CLI Usage

The oc set volume command uses the following general syntax:

$ oc set volume <object_selection> <operation> <mandatory_parameters> <optional_parameters>

This topic uses the form *<object_type>*/*<name>* for *<object_selection>* in later examples. However, you can choose one of the following options:

The *<operation>* can be one of --add, --remove, or --list.

Any *<mandatory_parameters>* or *<optional_parameters>* are specific to the selected operation and are discussed in later sections.

Adding Volumes

To add a volume, a volume mount, or both to pod templates:

$ oc set volume <object_type>/<name> --add [options]

Examples

Add a new volume source emptyDir to deployment configuration registry:

$ oc set volume dc/registry --add

Add volume v1 with secret secret1 for replication controller r1 and mount inside the containers at /data:

$ oc set volume rc/r1 --add --name=v1 --type=secret --secret-name='secret1' --mount-path=/data

Add existing persistent volume v1 with claim name pvc1 to deployment configuration dc.json on disk, mount the volume on container c1 at /data, and update the deployment configuration on the server:

$ oc set volume -f dc.json --add --name=v1 --type=persistentVolumeClaim \
  --claim-name=pvc1 --mount-path=/data --containers=c1

Updating Volumes

Updating existing volumes or volume mounts is the same as adding volumes, but with the --overwrite option:

$ oc set volume <object_type>/<name> --add --overwrite [options]

Examples

Replace existing volume v1 for replication controller r1 with existing persistent volume claim pvc1:

$ oc set volume rc/r1 --add --overwrite --name=v1 --type=persistentVolumeClaim --claim-name=pvc1

Change deployment configuration d1 mount point to /opt for volume v1:

$ oc set volume dc/d1 --add --overwrite --name=v1 --mount-path=/opt

Removing Volumes

To remove a volume or volume mount from pod templates:

$ oc set volume <object_type>/<name> --remove [options]

Examples

Remove a volume v1 from deployment configuration d1:

$ oc set volume dc/d1 --remove --name=v1

Unmount volume v1 from container c1 for deployment configuration d1 and remove the volume v1 if it is not referenced by any containers on d1:

$ oc set volume dc/d1 --remove --name=v1 --containers=c1

Remove all volumes for replication controller r1:

$ oc set volume rc/r1 --remove --confirm

Listing Volumes

To list volumes or volume mounts for pods or pod templates:

$ oc set volume <object_type>/<name> --list [options]

List volume supported options:

Examples

List all volumes for pod p1:

$ oc set volume pod/p1 --list

List volume v1 defined on all deployment configurations:

$ oc set volume dc --all --name=v1

Specifying a Sub-path

Use the volumeMounts.subPath property to specify a subPath inside a volume instead of the volume’s root. subPath allows you to share one volume for multiple uses in a single pod.

To view the list of files in the volume, run the oc rsh command:

$ oc rsh <pod>
sh-4.2$ ls /path/to/volume/subpath/mount
example_file1 example_file2 example_file3

Specify the subPath:

Example subPath Usage

apiVersion: v1
kind: Pod
metadata:
  name: my-site
spec:
    containers:
    - name: mysql
      image: mysql
      volumeMounts:
      - mountPath: /var/lib/mysql
        name: site-data
        subPath: mysql (1)
    - name: php
      image: php
      volumeMounts:
      - mountPath: /var/www/html
        name: site-data
        subPath: html (2)
    volumes:
    - name: site-data
      persistentVolumeClaim:
        claimName: my-site-data