apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotClass
metadata:
name: csi-hostpath-snap
driver: hostpath.csi.k8s.io (1)
deletionPolicy: Delete
This document describes how to use volume snapshots with supported Container Storage Interface (CSI) drivers to help protect against data loss in OKD. Familiarity with persistent volumes is suggested.
A snapshot represents the state of the storage volume in a cluster at a particular point in time. Volume snapshots can be used to provision a new volume.
OKD supports CSI volume snapshots by default. However, a specific CSI driver is required.
With CSI volume snapshots, a cluster administrator can:
Deploy a third-party CSI driver that supports snapshots.
Create a new persistent volume claim (PVC) from an existing volume snapshot.
Take a snapshot of an existing PVC.
Restore a snapshot as a different PVC.
Delete an existing volume snapshot.
With CSI volume snapshots, an app developer can:
Use volume snapshots as building blocks for developing application- or cluster-level storage backup solutions.
Rapidly rollback to a previous development version.
Use storage more efficiently by not having to make a full copy each time.
Be aware of the following when using volume snapshots:
Support is only available for CSI drivers. In-tree and FlexVolumes are not supported.
OKD only ships with select CSI drivers. For CSI drivers that are not provided by an OKD Driver Operator, it is recommended to use the CSI drivers provided by community or storage vendors. Follow the installation instructions provided by the CSI driver.
CSI drivers may or may not have implemented the volume snapshot functionality. CSI drivers that have provided support for volume snapshots will likely use the csi-external-snapshotter
sidecar. See documentation provided by the CSI driver for details.
OKD provides a snapshot controller that is deployed into the control plane. In addition, your CSI driver vendor provides the CSI snapshot sidecar as a helper container that is installed during the CSI driver installation.
The CSI snapshot controller and sidecar provide volume snapshotting through the OKD API. These external components run in the cluster.
The external controller is deployed by the CSI Snapshot Controller Operator.
The CSI snapshot controller binds VolumeSnapshot
and VolumeSnapshotContent
objects. The controller manages dynamic provisioning by creating and deleting VolumeSnapshotContent
objects.
Your CSI driver vendor provides the csi-external-snapshotter
sidecar. This is a separate helper container that is deployed with the CSI driver. The sidecar manages snapshots by triggering CreateSnapshot
and DeleteSnapshot
operations. Follow the installation instructions provided by your vendor.
The CSI Snapshot Controller Operator runs in the openshift-cluster-storage-operator
namespace. It is installed by the Cluster Version Operator (CVO) in all clusters by default.
The CSI Snapshot Controller Operator installs the CSI snapshot controller, which runs in the openshift-cluster-storage-operator
namespace.
During OKD installation, the CSI Snapshot Controller Operator creates the following snapshot custom resource definitions (CRDs) in the snapshot.storage.k8s.io/v1
API group:
VolumeSnapshotContent
A snapshot taken of a volume in the cluster that has been provisioned by a cluster administrator.
Similar to the PersistentVolume
object, the VolumeSnapshotContent
CRD is a cluster resource that points to a real snapshot in the storage back end.
For manually pre-provisioned snapshots, a cluster administrator creates a number of VolumeSnapshotContent
CRDs. These carry the details of the real volume snapshot in the storage system.
The VolumeSnapshotContent
CRD is not namespaced and is for use by a cluster administrator.
VolumeSnapshot
Similar to the PersistentVolumeClaim
object, the VolumeSnapshot
CRD defines a developer request for a snapshot. The CSI Snapshot Controller Operator runs the CSI snapshot controller, which handles the binding of a VolumeSnapshot
CRD with an appropriate VolumeSnapshotContent
CRD. The binding is a one-to-one mapping.
The VolumeSnapshot
CRD is namespaced. A developer uses the CRD as a distinct request for a snapshot.
VolumeSnapshotClass
Allows a cluster administrator to specify different attributes belonging to a VolumeSnapshot
object. These attributes may differ among snapshots taken of the same volume on the storage system, in which case they would not be expressed by using the same storage class of a persistent volume claim.
The VolumeSnapshotClass
CRD defines the parameters for the csi-external-snapshotter
sidecar to use when creating a snapshot. This allows the storage back end to know what kind of snapshot to dynamically create if multiple options are supported.
Dynamically provisioned snapshots use the VolumeSnapshotClass
CRD to specify storage-provider-specific parameters to use when creating a snapshot.
The VolumeSnapshotContentClass
CRD is not namespaced and is for use by a cluster administrator to enable global configuration options for their storage back end.
When you create a VolumeSnapshot
object, OKD creates a volume snapshot.
Logged in to a running OKD cluster.
A PVC created using a CSI driver that supports VolumeSnapshot
objects.
A storage class to provision the storage back end.
No pods are using the persistent volume claim (PVC) that you want to take a snapshot of.
Do not create a volume snapshot of a PVC if a pod is using it. Doing so might cause data corruption because the PVC is not quiesced (paused). Be sure to first tear down a running pod to ensure consistent snapshots. |
To dynamically create a volume snapshot:
Create a file with the VolumeSnapshotClass
object described by the following YAML:
apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotClass
metadata:
name: csi-hostpath-snap
driver: hostpath.csi.k8s.io (1)
deletionPolicy: Delete
1 | The name of the CSI driver that is used to create snapshots of this VolumeSnapshotClass object. The name must be the same as the Provisioner field of the storage class that is responsible for the PVC that is being snapshotted. |
Create the object you saved in the previous step by entering the following command:
$ oc create -f volumesnapshotclass.yaml
Create a VolumeSnapshot
object:
apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
name: mysnap
spec:
volumeSnapshotClassName: csi-hostpath-snap (1)
source:
persistentVolumeClaimName: myclaim (2)
1 | The request for a particular class by the volume snapshot. If the volumeSnapshotClassName setting is absent and there is a default volume snapshot class, a snapshot is created with the default volume snapshot class name. But if the field is absent and no default volume snapshot class exists, then no snapshot is created. |
2 | The name of the PersistentVolumeClaim object bound to a persistent volume. This defines what you want to create a snapshot of. Required for dynamically provisioning a snapshot. |
Create the object you saved in the previous step by entering the following command:
$ oc create -f volumesnapshot-dynamic.yaml
To manually provision a snapshot:
Provide a value for the volumeSnapshotContentName
parameter as the source for the snapshot, in addition to defining volume snapshot class as shown above.
apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
name: snapshot-demo
spec:
source:
volumeSnapshotContentName: mycontent (1)
1 | The volumeSnapshotContentName parameter is required for pre-provisioned snapshots. |
Create the object you saved in the previous step by entering the following command:
$ oc create -f volumesnapshot-manual.yaml
After the snapshot has been created in the cluster, additional details about the snapshot are available.
To display details about the volume snapshot that was created, enter the following command:
$ oc describe volumesnapshot mysnap
The following example displays details about the mysnap
volume snapshot:
apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
name: mysnap
spec:
source:
persistentVolumeClaimName: myclaim
volumeSnapshotClassName: csi-hostpath-snap
status:
boundVolumeSnapshotContentName: snapcontent-1af4989e-a365-4286-96f8-d5dcd65d78d6 (1)
creationTime: "2020-01-29T12:24:30Z" (2)
readyToUse: true (3)
restoreSize: 500Mi
1 | The pointer to the actual storage content that was created by the controller. |
2 | The time when the snapshot was created. The snapshot contains the volume content that was available at this indicated time. |
3 | If the value is set to true , the snapshot can be used to restore as a new PVC.
If the value is set to false , the snapshot was created. However, the storage back end needs to perform additional tasks to make the snapshot usable so that it can be restored as a new volume. For example, Amazon Elastic Block Store data might be moved to a different, less expensive location, which can take several minutes. |
To verify that the volume snapshot was created, enter the following command:
$ oc get volumesnapshotcontent
The pointer to the actual content is displayed. If the boundVolumeSnapshotContentName
field is populated, a VolumeSnapshotContent
object exists and the snapshot was created.
To verify that the snapshot is ready, confirm that the VolumeSnapshot
object has readyToUse: true
.
You can configure how OKD deletes volume snapshots.
Specify the deletion policy that you require in the VolumeSnapshotClass
object, as shown in the following example:
apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotClass
metadata:
name: csi-hostpath-snap
driver: hostpath.csi.k8s.io
deletionPolicy: Delete (1)
1 | When deleting the volume snapshot, if the Delete value is set, the underlying snapshot is deleted along with the VolumeSnapshotContent object. If the Retain value is set, both the underlying snapshot and VolumeSnapshotContent object remain.
If the Retain value is set and the VolumeSnapshot object is deleted without deleting the corresponding VolumeSnapshotContent object, the content remains. The snapshot itself is also retained in the storage back end. |
Delete the volume snapshot by entering the following command:
$ oc delete volumesnapshot <volumesnapshot_name>
volumesnapshot.snapshot.storage.k8s.io "mysnapshot" deleted
If the deletion policy is set to Retain
, delete the volume snapshot content by entering the following command:
$ oc delete volumesnapshotcontent <volumesnapshotcontent_name>
Optional: If the VolumeSnapshot
object is not successfully deleted, enter the following command to remove any finalizers for the leftover resource so that the delete operation can continue:
Only remove the finalizers if you are confident that there are no existing references from either persistent volume claims or volume snapshot contents to the |
$ oc patch -n $PROJECT volumesnapshot/$NAME --type=merge -p '{"metadata": {"finalizers":null}}'
volumesnapshotclass.snapshot.storage.k8s.io "csi-ocs-rbd-snapclass" deleted
The finalizers are removed and the volume snapshot is deleted.
The VolumeSnapshot
CRD content can be used to restore the existing volume to a previous state.
After your VolumeSnapshot
CRD is bound and the readyToUse
value is set to true
, you can use that resource to provision a new volume that is pre-populated with data from the snapshot.
.Prerequisites
* Logged in to a running OKD cluster.
* A persistent volume claim (PVC) created using a Container Storage Interface (CSI) driver that supports volume snapshots.
* A storage class to provision the storage back end.
* A volume snapshot has been created and is ready to use.
Specify a VolumeSnapshot
data source on a PVC as shown in the following:
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: myclaim-restore
spec:
storageClassName: csi-hostpath-sc
dataSource:
name: mysnap (1)
kind: VolumeSnapshot (2)
apiGroup: snapshot.storage.k8s.io (3)
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 1Gi
1 | Name of the VolumeSnapshot object representing the snapshot to use as source. |
2 | Must be set to the VolumeSnapshot value. |
3 | Must be set to the snapshot.storage.k8s.io value. |
Create a PVC by entering the following command:
$ oc create -f pvc-restore.yaml
Verify that the restored PVC has been created by entering the following command:
$ oc get pvc
A new PVC such as myclaim-restore
is displayed.