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 this section.

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

Prerequisite: CSI snapshot support needs to be enabled on your cluster. If your kubernetes distribution does not provide the kubernetes snapshot controller as well as the snapshot related custom resource definitions, you need to manually deploy them. For more information, see Enable CSI Snapshot Support.

Create a Backup via the CSI Mechanism

To create a backup using the CSI mechanism, create a Kubernetes VolumeSnapshot object via kubectl. An example is here.

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 bs://backup-volume/backup-name.

How the CSI Mechanism Works

When the VolumeSnapshot object is created with kubectl, the VolumeSnapshot.uuid 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.

Viewing the Backup

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

For information on how to restore a volume via a VolumeSnapshot object, refer to this page.

Example VolumeSnapshot

An example VolumeSnapshot object is below. The source needs to point to the PVC of the Longhorn volume for which a backup should be created.

The volumeSnapshotClassName field points to a VolumeSnapshotClass.

We create a default class named longhorn, which uses Delete as its deletionPolicy.

apiVersion: snapshot.storage.k8s.io/v1beta1
kind: VolumeSnapshot
metadata:
  name: test-snapshot-pvc
spec:
  volumeSnapshotClassName: longhorn
  source:
    persistentVolumeClaimName: test-vol

If you want the associated backup for a volume to be retained when the VolumeSnapshot is deleted, create a new VolumeSnapshotClass with Retain set as the deletionPolicy.

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