OpenShift Volume Concepts: Difference between revisions
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==EmptyDir== | ==EmptyDir== | ||
{{External|https://docs.openshift.com/container-platform/latest/dev_guide/volumes.html#dev-guide-volumes}} | |||
{{External|https://kubernetes.io/docs/concepts/storage/volumes/#emptydir}} | |||
An "emptyDir", also known as a "temporary pod volume", is created when the pod is assigned to a node, and exists as long as the pod is running on the node. It is initially empty. Containers in a pod can all read and write the same files in the "emptyDir" volume, though the volume can be mounted at the same or different paths in each container. | |||
When the pod is removed from the node, the data is deleted. If the container crashes, that does not remove the pod from a node, so data in an empty dir is safe across container crashes. | |||
The "emptyDir" volumes are stored on whatever medium is backing the node (disk, network storage). The mapping on the local file system backing the node can be discovered by identifying the container and then executing a [[docker inspect]]: | |||
<syntaxhighlight lang='json'> | |||
"Mounts": [ | |||
{ | |||
"Source": "/var/lib/origin/openshift.local.volumes/pods/1806c74f-0ad4-11e8-85a1-525400360e56/volumes/kubernetes.io~empty-dir/emptydirvol1", | |||
"Destination": "/something", | |||
"Mode": "Z", | |||
"RW": true, | |||
"Propagation": "rprivate" | |||
} | |||
... | |||
</syntaxhighlight> | |||
===EmptyDir Operations=== | |||
{{Internal|Oc_set#EmptyDir_Volume|Adding an EmptyDir Volume}} | |||
==ConfigMap== | ==ConfigMap== | ||
Revision as of 01:29, 6 February 2018
Internal
The Volume Mechanism
Volumes are mounted filesystems available to pods and their containers. Volumes may be backed by a number of host-local or network attached storage endpoints. The simplest volume type is EmptyDir, which is a temporary directory on a single machine. Administrators may also allow to request and attach Persistent Volumes.
Various contexts list the following objects as "volumes":
Volume Types
Persistent Volume Claim
A persistent volume claim is a request for a persistence resource with specific attributes, such as storage size. Persistent volume claims are matched to available volumes and binds the pod to the volume. This process allows a claim to be used as a volume in a pod: OpenShift finds the volume backing the claim and mounts it into the pod. Persistent volume claims are project-specific objects.
The pod can be disassociated from the persistent volume by deleting the persistent volume claim. The persistent volume transitions from a "Bound" to "Released" state. To make the persistent volume "Available" again, edit it and remove the persistent volume claim reference, as shown here. Transitioning the persistent volume from "Released" to "Available" state does not clear the storage content - this will have to be done manually.
All persistent volume claims for the current project can be listed with:
oc get pvc
EmptyDir
An "emptyDir", also known as a "temporary pod volume", is created when the pod is assigned to a node, and exists as long as the pod is running on the node. It is initially empty. Containers in a pod can all read and write the same files in the "emptyDir" volume, though the volume can be mounted at the same or different paths in each container.
When the pod is removed from the node, the data is deleted. If the container crashes, that does not remove the pod from a node, so data in an empty dir is safe across container crashes.
The "emptyDir" volumes are stored on whatever medium is backing the node (disk, network storage). The mapping on the local file system backing the node can be discovered by identifying the container and then executing a docker inspect:
"Mounts": [
{
"Source": "/var/lib/origin/openshift.local.volumes/pods/1806c74f-0ad4-11e8-85a1-525400360e56/volumes/kubernetes.io~empty-dir/emptydirvol1",
"Destination": "/something",
"Mode": "Z",
"RW": true,
"Propagation": "rprivate"
}
...
EmptyDir Operations
ConfigMap
Downward API
Host Path
Secret
NFS
Persistent Volume
Persistent volumes can be listed with oc get pv.