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, {product-title} 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.
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Note
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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.
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:
| Syntax | Description | Example |
|---|---|---|
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Selects |
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Selects |
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Selects resources of type |
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Selects all resources of type |
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File name, directory, or URL to file to use to edit the resource. |
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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.
To add a volume, a volume mount, or both to pod templates:
$ oc set volume <object_type>/<name> --add [options]
| Option | Description | Default |
|---|---|---|
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Name of the volume. |
Automatically generated, if not specified. |
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Name of the volume source. Supported values: |
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Select containers by name. It can also take wildcard |
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Mount path inside the selected containers. |
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Host path. Mandatory parameter for |
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Name of the secret. Mandatory parameter for |
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Name of the configmap. Mandatory parameter for |
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Name of the persistent volume claim. Mandatory parameter for
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Details of volume source as a JSON string. Recommended if the desired volume
source is not supported by |
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Display the modified objects instead of updating them on the server. Supported
values: |
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Output the modified objects with the given version. |
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Add a new volume source emptyDir to deployment configuration registry:
$ oc set volume dc/registry --add
Add volume v1 with secret $ecret for replication controller r1 and mount inside the containers at /data:
$ oc set 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 set 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 set volume rc --all --add --name=v1 \
--source='{"gitRepo": {
"repository": "https://github.com/namespace1/project1",
"revision": "5125c45f9f563"
}}'
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]
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
To remove a volume or volume mount from pod templates:
$ oc set volume <object_type>/<name> --remove [options]
| Option | Description | Default |
|---|---|---|
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Name of the volume. |
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Select containers by name. It can also take wildcard |
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Indicate that you want to remove multiple volumes at once. |
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Display the modified objects instead of updating them on the server. Supported
values: |
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Output the modified objects with the given version. |
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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
To list volumes or volume mounts for pods or pod templates:
$ oc set volume <object_type>/<name> --list [options]
List volume supported options:
| Option | Description | Default |
|---|---|---|
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Name of the volume. |
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Select containers by name. It can also take wildcard |
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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
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:
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
-
Databases are stored in the
mysqlfolder. -
HTML content is stored in the
htmlfolder.