snapshot.md

How to Create Volume Snapshots and Restore Volumes from Snapshots in Kubernetes Clusters

You must have an existing volume in use in your cluster, which you can create by creating a PersistentVolumeClaim (PVC). For the purposes of this tutorial, presume we have already created a PVC by calling kubectl create -f your_pvc_file.yaml with a YAML file that looks like this:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: cstor-pvc
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 5Gi
  storageClassName: cstor-csi-disk

The example detailed below explains the constructs required for working with snapshots and shows how snapshots can be created and used. Before creating a Volume Snapshot, a VolumeSnapshotClass must be set up.

kind: VolumeSnapshotClass
apiVersion: snapshot.storage.k8s.io/v1
metadata:
  name: csi-cstor-snapshotclass
  annotations:
    snapshot.storage.kubernetes.io/is-default-class: "true"
driver: cstor.csi.openebs.io
deletionPolicy: Delete

The driver points to OpenEBS CStor CSI driver. The deletionPolicy can be set to Delete or Retain. When set to Retain, the underlying physical snapshot on the storage cluster is retained even when the VolumeSnapshot object is deleted.

Note: In some cluster like OpenShift(OCP) 4.5, which only installs the v1beta1 version of VolumeSnapshotClass as supported version, then you may get the API error like:

$ kubectl apply -f snapshotclass.yaml
no matches for kind "VolumeSnapshotClass" in version "snapshot.storage.k8s.io/v1"

in such cases you can change the apiVersion to use v1beta1 version instead of v1 shown below:

kind: VolumeSnapshotClass
apiVersion: snapshot.storage.k8s.io/v1beta1
metadata:
  name: csi-cstor-snapshotclass
  annotations:
    snapshot.storage.kubernetes.io/is-default-class: "true"
driver: cstor.csi.openebs.io
deletionPolicy: Delete

Create a Snapshot of a Volume

To create a snapshot of a volume, here's an example of a YAML file that defines a snapshot:

apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  name: cstor-pvc-snap
spec:
  volumeSnapshotClassName: csi-cstor-snapshotclass
  source:
    persistentVolumeClaimName: cstor-pvc

The snapshot is being created for a PVC named cstor-pvc, and the name of the snapshot is set to cstor-pvc-snap.

$ kubectl create -f snapshot.yaml
volumesnapshot.snapshot.storage.k8s.io/cstor-pvc-snap created

$ kubectl get volumesnapshots
NAME                   AGE
cstor-pvc-snap              10s

This created a VolumeSnapshot object. A VolumeSnapshot is analogous to a PVC and is associated with a VolumeSnapshotContent object that represents the actual snapshot. To identify the VolumeSnapshotContent object for the cstor-pvc-snap VolumeSnapshot by describing it.

$ kubectl describe volumesnapshots cstor-pvc-snap
Name:         cstor-pvc-snap
Namespace:    default
.
.
.
Spec:
  Snapshot Class Name:    cstor-csi-snapshotclass
  Snapshot Content Name:  snapcontent-e8d8a0ca-9826-11e9-9807-525400f3f660
  Source:
    API Group:
    Kind:       PersistentVolumeClaim
    Name:       cstor-pvc
Status:
  Creation Time:  2020-06-20T15:27:29Z
  Ready To Use:   true
  Restore Size:   5Gi
.
.

The SnapshotContentName identifies the VolumeSnapshotContent object which serves this snapshot. The Ready To Use parameter indicates that the Snapshot created successfully and can be used to create a new PVC.

Note: In some cluster like OpenShift(OCP) 4.5, which only installs the v1beta1 version of VolumeSnapshots as supported version, then you may get the API error like:

$ kubectl apply -f snapshot.yaml
no matches for kind "VolumeSnapshot" in version "snapshot.storage.k8s.io/v1"

in such cases you can change the apiVersion to use v1beta1 version instead of v1 shown below:

apiVersion: snapshot.storage.k8s.io/v1beta1
kind: VolumeSnapshot
metadata:
  name: cstor-pvc-snap
spec:
  volumeSnapshotClassName: csi-cstor-snapshotclass
  source:
    persistentVolumeClaimName: cstor-pvc

Create PVCs from VolumeSnapshots

To restore from a given snapshot, you need to create a new PVC that refers to the snapshot.Here's an example of a YAML file that restores from a snapshot and creates a new PVC:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: restore-cstor-pvc
spec:
  storageClassName: cstor-csi-disk
  dataSource:
    name: cstor-pvc-snap
    kind: VolumeSnapshot
    apiGroup: snapshot.storage.k8s.io
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 5Gi

The dataSource shows that the PVC must be created using a VolumeSnapshot named cstor-pvc-snap as the source of the data. This instructs CStor CSI to create a PVC from the snapshot. Once the PVC is created, it can be attached to a pod and used just like any other PVC.

5. Verify that the PVC has been successfully created:

kubectl get pvc
NAME                           STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS              AGE
cstor-pvc                      Bound    pvc-52d88903-0518-11ea-b887-42010a80006c   5Gi        RWO            cstor-csi-disk            1d
restore-cstor-pvc              Bound    pvc-2f2d65fc-0784-11ea-b887-42010a80006c   5Gi        RWO            cstor-csi-disk            5s