Backups in Longhorn are objects in an off-cluster backupstore, and the endpoint to access the backupstore is the backup target. For more information, see

To programmatically create backups, you can use the generic Kubernetes CSI VolumeSnapshot mechanism. To learn more about the CSI VolumeSnapshot mechanism, click here.

To create a CSI VolumeSnapshot associated with a Longhorn backup, you first need to create a VolumeSnapshotClass object with the parameter type set to bak as follow:

For more information about VolumeSnapshotClass, see the kubernetes documentation for VolumeSnapshotClasses.

After that, create a Kubernetes VolumeSnapshot object with volumeSnapshotClassName points to the name of the VolumeSnapshotClass (longhorn-backup-vsc) and the source points to the PVC of the Longhorn volume for which a backup should be created.

Result: A backup is created. The VolumeSnapshot object creation leads to the creation of a VolumeSnapshotContent Kubernetes object. The VolumeSnapshotContent refers to a Longhorn backup in its VolumeSnapshotContent.snapshotHandle field with the name bak://backup-volume/backup-name.

To see the backup, click Backup in the top navigation bar and navigate to the backup-volume mentioned in the VolumeSnapshotContent.snapshotHandle.

How the CSI Mechanism Works in this Scenario

When the VolumeSnapshot object is created with kubectl, the field is used to identify a Longhorn snapshot and the associated VolumeSnapshotContent object.

This creates a new Longhorn snapshot named snapshot-uuid.

Then a backup of that snapshot is initiated, and the CSI request returns.

Afterwards a VolumeSnapshotContent object named snapcontent-uuid is created.

The CSI snapshotter sidecar periodically queries the Longhorn CSI plugin to evaluate the backup status.

Once the backup is completed, the VolumeSnapshotContent.readyToUse flag is set to true.

Create a PersistentVolumeClaim object where the dataSource field points to an existing VolumeSnapshot object that is associated with Longhorn backup.

The csi-provisioner will pick this up and instruct the Longhorn CSI driver to provision a new volume with the data from the associated backup.

Note that the spec.resources.requests.storage value must be the same as the size of VolumeSnapshot object.

Restore a Longhorn Backup that Has No Associated VolumeSnapshot

You can use the CSI mechanism to restore Longhorn backups that have not been created via the CSI mechanism. To restore Longhorn backups that have not been created via the CSI mechanism, you have to first manually create a VolumeSnapshot and VolumeSnapshotContent object for the backup.

Create a object with the snapshotHandle field set to bak://backup-volume/backup-name.

The backup-volume and backup-name values can be retrieved from the Backup page in the Longhorn UI.

Create the associated VolumeSnapshot object with the name field set to test-snapshot-existing-backup, where the source field refers to a VolumeSnapshotContent object via the volumeSnapshotContentName field.

This differs from the creation of a backup, in which case the source field refers to a PerstistentVolumeClaim via the persistentVolumeClaimName field.

Only one type of reference can be set for a VolumeSnapshot object.

Now you can create a PerstistantVolumeClaim object that refers to the newly created VolumeSnapshot object. For an example see above.