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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, OpenShift Container Platform 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.

emptyDir volume storage may be restricted by a quota based on the pod’s FSGroup, if the FSGroup parameter is enabled by your cluster administrator.

You can use the CLI command oc 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 volume command uses the following general syntax:

$ oc 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:

Table 1. Object Selection
Syntax Description Example

<object_type> <name>

Selects <name> of type <object_type>.

deploymentConfig registry

<object_type>/<name>

Selects <name> of type <object_type>.

deploymentConfig/registry

<object_type> --selector=<object_label_selector>

Selects resources of type <object_type> that matched the given label selector.

deploymentConfig --selector="name=registry"

<object_type> --all

Selects all resources of type <object_type>.

deploymentConfig --all

-f or --filename=<file_name>

File name, directory, or URL to file to use to edit the resource.

-f registry-deployment-config.json

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 volume <object_type>/<name> --add [options]
Table 2. Supported Options for Adding Volumes
Option Description Default

--name

Name of the volume.

Automatically generated, if not specified.

-t, --type

Name of the volume source. Supported values: emptyDir, hostPath, secret, configmap, persistentVolumeClaim or projected.

emptyDir

-c, --containers

Select containers by name. It can also take wildcard '*' that matches any character.

'*'

-m, --mount-path

Mount path inside the selected containers.

--path

Host path. Mandatory parameter for --type=hostPath.

--secret-name

Name of the secret. Mandatory parameter for --type=secret.

--configmap-name

Name of the configmap. Mandatory parameter for --type=configmap.

--claim-name

Name of the persistent volume claim. Mandatory parameter for --type=persistentVolumeClaim.

--source

Details of volume source as a JSON string. Recommended if the desired volume source is not supported by --type. See available volume sources

-o, --output

Display the modified objects instead of updating them on the server. Supported values: json, yaml.

--output-version

Output the modified objects with the given version.

api-version

Examples

Add a new volume source emptyDir to deployment configuration registry:

$ oc volume dc/registry --add

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

$ oc volume rc/r1 --add --name=v1 --type=secret --secret-name='$ecret' --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 volume -f dc.json --add --name=v1 --type=persistentVolumeClaim \
  --claim-name=pvc1 --mount-path=/data --containers=c1

Add volume v1 based on Git repository https://github.com/namespace1/project1 with revision 5125c45f9f563 for all replication controllers:

$ oc volume rc --all --add --name=v1 \
  --source='{"gitRepo": {
                "repository": "https://github.com/namespace1/project1",
                "revision": "5125c45f9f563"
            }}'

Updating Volumes

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

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

Examples

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

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

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

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

Removing Volumes

To remove a volume or volume mount from pod templates:

$ oc volume <object_type>/<name> --remove [options]
Table 3. Supported Options for Removing Volumes
Option Description Default

--name

Name of the volume.

-c, --containers

Select containers by name. It can also take wildcard '*' that matches any character.

'*'

--confirm

Indicate that you want to remove multiple volumes at once.

-o, --output

Display the modified objects instead of updating them on the server. Supported values: json, yaml.

--output-version

Output the modified objects with the given version.

api-version

Examples

Remove a volume v1 from deployment configuration d1:

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

Remove all volumes for replication controller r1:

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

Listing Volumes

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

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

List volume supported options:

Option Description Default

--name

Name of the volume.

-c, --containers

Select containers by name. It can also take wildcard '*' that matches any character.

'*'

Examples

List all volumes for pod p1:

$ oc volume pod/p1 --list

List volume v1 defined on all deployment configurations:

$ oc 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
1 Databases are stored in the mysql folder.
2 HTML content is stored in the html folder.