On-Demand Volume Snapshots

Beginning with the 20.01 release of Trident, it is now possible to use the Volume Snapshot feature to create snapshots of PVs at the Kubernetes layer. These snapshots can be used to maintain point-in-time copies of volumes that have been created by Trident and can also be used to schedule the creation of additional volumes (clones). This feature is available from Kubernetes 1.17 [Beta] and is GA from 1.20.

Note

Kubernetes Volume Snapshot is GA from Kubernetes 1.20. To understand the

changes involved in moving from beta to GA, take a look at the release blog. With the graduation to GA, the v1 API version is introduced and is backward compatible with v1beta1 snapshots.

Creating volume snapshots requires an external snapshot controller to be created, as well as some Custom Resource Definitions (CRDs). This is the responsibility of the Kubernetes orchestrator that is being used (E.g., Kubeadm, GKE, OpenShift). Check with your Kubernetes orchestrator to confirm these requirements are met. You can create an external snapshot-controller and snapshot CRDs using the code snippet below.

$ cat snapshot-setup.sh
#!/bin/bash
# Create volume snapshot CRDs
kubectl apply -f https://github.com/kubernetes-csi/external-snapshotter/tree/release-3.0/client/config/crd/snapshot.storage.k8s.io_volumesnapshotclasses.yaml
kubectl apply -f https://github.com/kubernetes-csi/external-snapshotter/tree/release-3.0/client/config/crd/snapshot.storage.k8s.io_volumesnapshotcontents.yaml
kubectl apply -f https://github.com/kubernetes-csi/external-snapshotter/tree/release-3.0/client/config/crd/snapshot.storage.k8s.io_volumesnapshots.yaml
# Create the snapshot-controller in the desired namespace. Edit the YAML manifests below to modify namespace.
kubectl apply -f https://raw.githubusercontent.com/kubernetes-csi/external-snapshotter/release-3.0/deploy/kubernetes/snapshot-controller/rbac-snapshot-controller.yaml
kubectl apply -f https://raw.githubusercontent.com/kubernetes-csi/external-snapshotter/release-3.0/deploy/kubernetes/snapshot-controller/setup-snapshot-controller.yaml

CSI Snapshotter provides a Validating Webhook to help users validate existing v1beta1 snapshots and confirm they are valid resource objects. The validating webhook will automatically label invalid snapshot objects and prevent the creation of future invalid objects. As with volume snapshot CRDs and the snapshot controller, the validating webhook is deployed by the Kubernetes orchestrator. Instructions to deploy the validating webhook manually can be found here. Examples of invalid snapshot manifests can be obtained in the examples directory of the external-snapshotter. repository.

Note

Volume snapshot is supported by the ontap-nas, ontap-san, ontap-san-economy, solidfire-san, aws-cvs, gcp-cvs and azure-netapp-files drivers. This feature requires Kubernetes 1.17 and above.

Trident handles the creation of VolumeSnapshots for its drivers as explained below:

  • For the ontap-nas, ontap-san, aws-cvs, gcp-cvs and azure-netapp-files drivers, each PV maps to a FlexVol. As a result, VolumeSnapshots are created as NetApp Snapshots. NetApp’s Snapshot technology delivers more stability, scalability, recoverability, and performance than competing snapshot technologies. These Snapshot copies are extremely efficient both in the time needed to create them and in storage space.
  • For the ontap-san-economy driver, PVs map to LUNs created on shared FlexVols. VolumeSnapshots of PVs are achieved by performing FlexClones of the associated LUN. ONTAP’s FlexClone technology makes it possible to create copies of even the largest datasets almost instantaneously. Copies share data blocks with their parents, consuming no storage except what is required for metadata.
  • For the solidfire-san driver, each PV maps to a LUN created on the Element/HCI cluster. VolumeSnapshots are represented by Element snapshots of the underlying LUN. These snapshots are point-in-time copies and only take up a small amount of system resources and space.

With Trident, you can use VolumeSnapshots to create new PVs from them. Creating PVs from these snapshots is performed by using the FlexClone technology for supported ONTAP & CVS backends. When creating a PV from a snapshot, the backing volume is a FlexClone of the snapshot’s parent volume. The solidfire-san driver uses ElementOS volume clones to create PVs from snapshots. Here it creates a clone from the Element snapshot.

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.

$ cat snap-sc.yaml
#Use apiVersion v1 for Kubernetes 1.20 and above. For Kubernetes 1.17 - 1.19, use apiVersion v1beta1.
apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotClass
metadata:
  name: csi-snapclass
driver: csi.trident.netapp.io
deletionPolicy: Delete

The driver points to Trident’s 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.

Create a VolumeSnapshot

We can now create a snapshot of an existing PVC.

$ cat snap.yaml
#Use apiVersion v1 for Kubernetes 1.20 and above. For Kubernetes 1.17 - 1.19, use apiVersion v1beta1.
apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  name: pvc1-snap
spec:
  volumeSnapshotClassName: csi-snapclass
  source:
    persistentVolumeClaimName: pvc1

The snapshot is being created for a PVC named pvc1, and the name of the snapshot is set to pvc1-snap.

$ kubectl create -f snap.yaml
volumesnapshot.snapshot.storage.k8s.io/pvc1-snap created

$ kubectl get volumesnapshots
NAME                   AGE
pvc1-snap              50s

This created a VolumeSnapshot object. A VolumeSnapshot is analogous to a PVC and is associated with a VolumeSnapshotContent object that represents the actual snapshot.

It is possible to identify the VolumeSnapshotContent object for the pvc1-snap VolumeSnapshot by describing it.

$ kubectl describe volumesnapshots pvc1-snap
Name:         pvc1-snap
Namespace:    default
.
.
.
Spec:
  Snapshot Class Name:    pvc1-snap
  Snapshot Content Name:  snapcontent-e8d8a0ca-9826-11e9-9807-525400f3f660
  Source:
    API Group:
    Kind:       PersistentVolumeClaim
    Name:       pvc1
Status:
  Creation Time:  2019-06-26T15:27:29Z
  Ready To Use:   true
  Restore Size:   3Gi
.
.

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

Create PVCs from VolumeSnapshots

A PVC can be created using the snapshot as shown in the example below:

$ cat pvc-from-snap.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-from-snap
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: golden
  resources:
    requests:
      storage: 3Gi
  dataSource:
    name: pvc1-snap
    kind: VolumeSnapshot
    apiGroup: snapshot.storage.k8s.io

The dataSource shows that the PVC must be created using a VolumeSnapshot named pvc1-snap as the source of the data. This instructs Trident 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.

Note

When deleting a Persistent Volume with associated snapshots, the corresponding Trident volume is updated to a “Deleting state”. For the Trident volume to be deleted, the snapshots of the volume must be removed.