Taking a CSI VolumeGroupSnapshot requires three things on top of regular CSI snapshot support:

1. The VolumeGroupSnapshot CRDs.
2. The CSIVolumeGroupSnapshot feature gate enabled on the snapshot-controller.
3. The same feature gate enabled on the csi-snapshotter deployed by Longhorn.

Prerequisite: CSI snapshot support must be enabled on your cluster. See Enable CSI Snapshot Support.

Warning: Potential Snapshot Outage Install the VolumeGroupSnapshot CRDs before enabling the CSIVolumeGroupSnapshot feature gate on any component. If the feature gate is enabled while the CRDs are missing, the csi-snapshotter sidecar stops serving regular volume snapshots. Every VolumeSnapshot in the cluster will hang in the Pending state even though the sidecar pod reports Running.

Install the VolumeGroupSnapshot CRDs

The CRDs ship with external-snapshotter: VolumeGroupSnapshotClass, VolumeGroupSnapshot, and VolumeGroupSnapshotContent in the groupsnapshot.storage.k8s.io API group.

Use release v8.6.0 or later so they serve the v1 API. Replace <version> in the URLs below with your target release (e.g., v8.6.0) and apply:

kubectl apply -f https://raw.githubusercontent.com/kubernetes-csi/external-snapshotter/<version>/client/config/crd/groupsnapshot.storage.k8s.io_volumegroupsnapshotclasses.yaml
kubectl apply -f https://raw.githubusercontent.com/kubernetes-csi/external-snapshotter/<version>/client/config/crd/groupsnapshot.storage.k8s.io_volumegroupsnapshots.yaml
kubectl apply -f https://raw.githubusercontent.com/kubernetes-csi/external-snapshotter/<version>/client/config/crd/groupsnapshot.storage.k8s.io_volumegroupsnapshotcontents.yaml

Enable the Feature Gate on the snapshot-controller

The snapshot-controller processes VolumeGroupSnapshot objects only when its CSIVolumeGroupSnapshot feature gate is on. The controller must also be from external-snapshotter v8.6.0 or later.

Add the feature gate to the controller arguments, adjusting the namespace to where your snapshot-controller is deployed (default is kube-system):

kubectl -n kube-system patch deploy snapshot-controller --type=json \
  -p='[{"op":"add","path":"/spec/template/spec/containers/0/args/-","value":"--feature-gates=CSIVolumeGroupSnapshot=true"}]'

Enable VolumeGroupSnapshot Support in Longhorn

In Longhorn, VolumeGroupSnapshot support is off by default. Enabling it turns on the CSIVolumeGroupSnapshot feature gate of the csi-snapshotter that Longhorn deploys.

• For Helm installations: Set the chart value csi.volumeGroupSnapshotEnabled to true.

• For kubectl installations: Uncomment the CSI_VOLUME_GROUP_SNAPSHOT_ENABLED environment variable in the longhorn-driver-deployer Deployment of the deploy manifest:

  - name: CSI_VOLUME_GROUP_SNAPSHOT_ENABLED
    value: "true"
  

Troubleshooting:: When the Longhorn toggle is enabled but the VolumeGroupSnapshot CRDs are missing (or not served at v1), the Longhorn driver deployer will fail with an error naming the missing CRDs. However, regular per-volume snapshots will keep working. To recover, simply install the CRDs (or disable the toggle) and redeploy.