Project: Longhorn (Runtime / Cloud Native Storage)
File: 20220110-extend-csi-snapshot-to-support-longhorn-snapshot.md

Extend CSI snapshot to support Longhorn snapshot Before this feature, if the user uses , they can only create Longhorn backups (out of cluster). We want to extend the CSI Snapshotter to support creating for Longhorn snapshot (in-cluster) as well. https://github.com/longhorn/longhorn/issues/2534 Extend the CSI Snapshotter to support: Creating Longhorn snapshot Deleting Longhorn snapshot Creating a new PVC from a CSI snapshot that is associated with a Longhorn snapshot Longhorn snapshot Reverting is not a goal because CSI snapshotter doesn't support replace in place for now: https://github.com/container-storage-interface/spec/blob/master/spec.md#createsnapshot Before this feature is implemented, users can only use CSI Snapshotter to create/restore Longhorn backups. This means that users must set up a backup target outside of the cluster. Uploading/downloading data from backup target is a long/costly operation. Sometimes, users might just want to use CSI Snapshotter to take an in-cluster Longhorn snapshot and create a new volume from that snapshot. The Longhorn snapshot operation is cheap and faster than the backup operation and doesn't require setting up a backup target. To use this feature, users need to do: Deploy the CSI snapshot CRDs, Controller as instructed at https://longhorn.io/docs/1.2.3/snapshots-and-backups/csi-snapshot-support/enable-csi-snapshot-support/ Deploy a VolumeSnapshotClass with the parameter `type: longhorn-snapshot`. I.e., ```yaml kind: VolumeSnapshotClass apiVersion: snapshot.storage.k8s.io/v1beta1 metadata: name: longhorn-snapshot driver: driver.longhorn.io deletionPolicy: Delete parameters: type: longhorn-snapshot ``` To create a new CSI snapshot associated with a Longhorn snapshot of the volume `test-vol`, users deploy the following VolumeSnapshot CR: ```yaml apiVersion: snapshot.storage.k8s.io/v1beta1 kind: VolumeSnapshot metadata: name: test-snapshot spec: volumeSnapshotClassName: longhorn-snapshot source: persistentVolumeClaimName: test-vol ``` A new Longhorn snapshot is created for the volume `test-vol` To create a new PVC from the CSI snapshot, users can deploy the following yaml: ```yaml apiVersion: v1 kind: PersistentVolumeClaim metadata: name: test-restore-snapshot-pvc spec: storageClassName: longhorn dataSource: name: test-snapshot kind: VolumeSnapshot apiGroup: snapshot.storage.k8s.io accessModes: ReadWriteOnce resources: requests: storage: 5Gi # should be the same as the size of `test-vol` ``` A new PVC will be created with the same content as in the VolumeSnapshot `test-snapshot` Deleting the VolumeSnapshot `test-snapshot` will lead to the deletion of the corresponding Longhorn snapshot of the volume `test-vol` None We follow the specification in when supporting the CSI snapshot. We define a new parameter in the VolumeSnapshotClass `type`. The value of the parameter `type` can be `longhorn-snapshot` or `longhorn-backup`. When `type` is `longhorn-snapshot` it means that the CSI VolumeSnapshot created with this VolumeSnapshotClass is associated with a Longhorn snapshot. When `type` is `longhorn-backup` it means that the CSI VolumeSnapshot created with this VolumeSnapshotClass is associated with a Longhorn backup. In , we get the value of parameter

If it is `longhorn-backup`, we take a Longhorn backup as before. If it is `longhorn-snapshot` we do: Get the name of the Longhorn volume Check if the volume is in attached state. If it is not, return `codes.FailedPrecondition`. We cannot take a snapshot of non-attached volume. Check if a Longhorn snapshot with the same name as the requested CSI snapshot already exists. If yes, return OK without taking a new Longhorn snapshot. Take a new Longhorn snapshot. Encode the snapshotId in the format `snap://volume-name/snapshot-name`. This snaphotId will be used in the later CSI CreateVolume and DeleteSnapshot call. In : If the VolumeContentSource is a `VolumeContentSource_Snapshot` type, decode the snapshotId in the format from the above step. Create a new volume with the `dataSource` set to `snap://volume-name/snapshot-name`. This will trigger Longhorn to clone the content of the snapshot to the new volume. Note that if the source volume is not attached, Longhorn cannot verify the existence of the snapshot inside the Longhorn volume. This means that and new PVC cannot be provisioned. In : Decode the snapshotId in the format from the above step. If the type is `longhorn-backup` we delete the backup as before. If the type is `longhorn-snapshot`, we delete the corresponding Longhorn snapshot of the source volume. If the source volume or the snapshot is no longer exist, we return OK as specified in Integration test plan. Deploy the CSI snapshot CRDs, Controller as instructed at https://longhorn.io/docs/1.2.3/snapshots-and-backups/csi-snapshot-support/enable-csi-snapshot-support/ Deploy 4 VolumeSnapshotClass: ```yaml kind: VolumeSnapshotClass apiVersion: snapshot.storage.k8s.io/v1beta1 metadata: name: longhorn-backup-1 driver: driver.longhorn.io deletionPolicy: Delete ``` ```yaml kind: VolumeSnapshotClass apiVersion: snapshot.storage.k8s.io/v1beta1 metadata: name: longhorn-backup-2 driver: driver.longhorn.io deletionPolicy: Delete parameters: type: longhorn-backup ``` ```yaml kind: VolumeSnapshotClass apiVersion: snapshot.storage.k8s.io/v1beta1 metadata: name: longhorn-snapshot driver: driver.longhorn.io deletionPolicy: Delete parameters: type: longhorn-snapshot ``` ```yaml kind: VolumeSnapshotClass apiVersion: snapshot.storage.k8s.io/v1beta1 metadata: name: invalid-class driver: driver.longhorn.io deletionPolicy: Delete parameters: type: invalid ``` Create Longhorn volume `test-vol` of 5GB. Create PV/PVC for the Longhorn volume. Create a workload that uses the volume. Write some data to the volume. Make sure data persist to the volume by running `sync` Set up a backup target for Longhorn `type` is `longhorn-backup` or `""` Create a VolumeSnapshot with the following yaml ```yaml apiVersion: snapshot.storage.k8s.io/v1beta1 kind: VolumeSnapshot metadata: name: test-snapshot-longhorn-backup spec: volumeSnapshotClassName: longhorn-backup-1 source: persistentVolumeClaimName: test-vol ``` Verify that a backup is created. Delete the `test-snapshot-longhorn-backup` Verify that the backup is deleted Create the `test-snapshot-longhorn-backup` VolumeSnapshot with `volumeSnapshotClassName: longhorn-backup-2` Verify that a backup is created. `type` is `longhorn-snapshot` volume is in detached state. Scale down the workload of `test-vol` to detach the volume. Create `test-snapshot-longhorn-snapshot` VolumeSnapshot with `volumeSnapshotClassName: longhorn-snapshot`. Verify the error `volume

invalid state ... for taking snapshot` in the Longhorn CSI plugin. volume is in attached state. Scale up the workload to attach `test-vol` Verify that a Longhorn snapshot is created for the `test-vol`. invalid type Create `test-snapshot-invalid` VolumeSnapshot with `volumeSnapshotClassName: invalid-class`. Verify the error `invalid snapshot type: %v. Must be %v or %v or` in the Longhorn CSI plugin. Delete `test-snapshot-invalid` VolumeSnapshot. From `longhorn-backup` type Create a new PVC with the flowing yaml: ```yaml apiVersion: v1 kind: PersistentVolumeClaim metadata: name: test-restore-pvc spec: storageClassName: longhorn dataSource: name: test-snapshot-longhorn-backup kind: VolumeSnapshot apiGroup: snapshot.storage.k8s.io accessModes: ReadWriteOnce resources: requests: storage: 5Gi ``` Attach the PVC `test-restore-pvc` and verify the data Delete the PVC From `longhorn-snapshot` type Source volume is attached && Longhorn snapshot exist Create a PVC with the following yaml: ```yaml apiVersion: v1 kind: PersistentVolumeClaim metadata: name: test-restore-pvc spec: storageClassName: longhorn dataSource: name: test-snapshot-longhorn-snapshot kind: VolumeSnapshot apiGroup: snapshot.storage.k8s.io accessModes: ReadWriteOnce resources: requests: storage: 5Gi ``` Attach the PVC `test-restore-pvc` and verify the data Delete the PVC Source volume is detached Scale down the workload to detach the `test-vol` Create the same PVC `test-restore-pvc` as in the `Source volume is attached && Longhorn snapshot exist` section Verify that PVC provisioning failed because the source volume is detached so Longhorn cannot verify the existence of the Longhorn snapshot in the source volume. Scale up the workload to attach `test-vol` Wait for PVC to finish provisioning and be bounded Attach the PVC `test-restore-pvc` and verify the data Delete the PVC Source volume is attached && Longhorn snapshot doesnt exist Find the VolumeSnapshotContent of the VolumeSnapshot `test-snapshot-longhorn-snapshot`. Find the Longhorn snapshot name inside the field `VolumeSnapshotContent.snapshotHandle`. Go to Longhorn UI. Delete the Longhorn snapshot. Repeat steps in the section `Longhorn snapshot exist` above. PVC should be stuck in provisioning because Longhorn snapshot of the source volume doesn't exist. Delete the PVC `test-restore-pvc` PVC `longhorn-backup` type Done in the above step `longhorn-snapshot` type volume is attached && snapshot doesnt exist Delete the VolumeSnapshot `test-snapshot-longhorn-snapshot` and verify that the VolumeSnapshot is deleted. volume is attached && snapshot exist Recreate the VolumeSnapshot `test-snapshot-longhorn-snapshot` Verify the creation of Longhorn snapshot with the name in the field `VolumeSnapshotContent.snapshotHandle` Delete the VolumeSnapshot `test-snapshot-longhorn-snapshot` Verify that Longhorn snapshot is removed or marked as removed Verify that the VolumeSnapshot `test-snapshot-longhorn-snapshot` is deleted. volume is detached Recreate the VolumeSnapshot `test-snapshot-longhorn-snapshot` Scale down the workload to detach `test-vol` Delete the VolumeSnapshot `test-snapshot-longhorn-snapshot` Verify that VolumeSnapshot `test-snapshot-longhorn-snapshot` is stuck in deleting No upgrade strategy needed We need to update the docs and examples to reflect the new parameter in the VolumeSnapshotClass, `type`.