Project: Longhorn (Runtime / Cloud Native Storage)
File: 20200904-csi-snapshot-support.md

To allow users to create/restore/delete backups programmatically, we want to add support for the csi snapshot mechanism. This way existing tools can be used to create kubernetes `VolumeSnapshot` api resources, which we can react to in the csi plugin. https://github.com/longhorn/longhorn/issues/304 https://github.com/longhorn/longhorn/issues/610 https://github.com/longhorn/longhorn/issues/1127 https://github.com/kubernetes/community/blob/master/contributors/design-proposals/storage/csi-snapshot.md Provide user with programmatic access for backup operations via the standardized csi interface. https://kubernetes.io/docs/concepts/storage/volume-snapshots/#provisioning-volume-snapshot add csi snapshot support to our csi driver VolumeBackup crd refactor Changes to the longhorn backup code support csi CreateSnapshot call support csi DeleteSnapshot call support snapshot as ContentSource for restoration during CreateVolume calls Currently, it's hard for users to interact with the backup system programmatically, after this enhancement the users will be able to use the standard kubernetes csi mechanisms for backup creation / deletion and restoration of a new volume based on a backup. The user can request a backup of a volume by creation of a kubernetes `VolumeSnapshot` object. Example below for a volume named `test-vol` ```yaml apiVersion: snapshot.storage.k8s.io/v1beta1 kind: VolumeSnapshot metadata: name: test-snapshot-pvc spec: volumeSnapshotClassName: longhorn source: persistentVolumeClaimName: test-vol ``` The user can request the creation of a volume based on a prior created `VolumeSnapshot` object. Example below for a volume named `test-vol-restore` ```yaml apiVersion: v1 kind: PersistentVolumeClaim metadata: name: test-vol-restore spec: storageClassName: longhorn dataSource: name: test-vol-snapshot kind: VolumeSnapshot apiGroup: snapshot.storage.k8s.io accessModes: ReadWriteOnce resources: requests: storage: 2Gi ``` The user can request the creation of a volume based on a prior longhorn backup, that was not created via the csi layer. The user needs to create a `VolumeSnapshotContent` object with an associated `VolumeSnapshot` object. The `snapshotHandle` of the `VolumeSnapshotContent` needs to point to an existing longhorn backup. Example below for a volume named `test-restore-existing-backup` ```yaml apiVersion: snapshot.storage.k8s.io/v1beta1 kind: VolumeSnapshotContent metadata: name: test-existing-backup spec: volumeSnapshotClassName: longhorn driver: driver.longhorn.io deletionPolicy: Delete source: snapshotHandle: bs://test-vol/backup-625159fb469e492e volumeSnapshotRef: name: test-snapshot-existing-backup namespace: default ``` ```yaml apiVersion: snapshot.storage.k8s.io/v1beta1 kind: VolumeSnapshot metadata: name: test-snapshot-existing-backup spec: volumeSnapshotClassName: longhorn source: volumeSnapshotContentName: test-existing-backup ``` ```yaml apiVersion: v1 kind: PersistentVolumeClaim metadata: name: test-restore-existing-backup spec: storageClassName: longhorn dataSource: name: test-snapshot-existing-backup kind: VolumeSnapshot apiGroup: snapshot.storage.k8s.io accessModes: ReadWriteOnce resources: requests: storage: 2Gi ``` The user can request the deletion of a backup by removing the associated `VolumeSnapshot` object. If the DeletionPolicy is Delete, then the referenced longhorn backup will be deleted along with the `VolumeSnapshotContent` object. If the DeletionPolicy is Retain, then both the referenced longhorn backup and `VolumeSnapshotContent` object remain. The default DeletionPolicy is set to Delete, if the user wants to retain the longhorn backups, the user can create a snapshotClass with DeletionPolicy set to Retain. https://kubernetes.io/docs/concepts/storage/volume-snapshot-classes/#deletionpolicy Example below for a snapshot named `test-snapshot-pvc` `kubectl delete volumesnapshots test-snapshot-pvc` Deletion is triggered by deleting the VolumeSnapshot object, and the DeletionPolicy will be followed. The default deletion policy no changes necessary The creation of a `VolumeSnapshot` resource triggers the creation of a longhorn snapshot afterwards, that snapshot will be backed up via the longhorn backup mechanism to a user defined backupstore (s3, nfs). While the backup isn't completed the csi snapshot will be marked not ready to use. The csi-snapshot-request name is generated by the csi snapshotter, based on the configured prefix + `VolumeSnapshot.uuid` This information is also used to generate the `VolumeSnapshotContent.name = snapcontent-uuid` The csi-snapshotter will always call the longhorn csi plugin with the same csi snapshot request name for a specific Snapshot

This means we have to use the csi snapshotter generated name, for the longhorn snapshot or introduce a CRD (VolumeBackup) so that we have a persisted way of associating csiSnapshot - longhornSnapshot - longhornBackup If we would ignore the requested name, we would end up generating a new snapshot for each successive call, since a backup can take a long time for very big volumes, that would not be the desired behavior. To be able to lookup the backup during a following `DeleteSnapshot` or `CreateVolume` call, we encode the backupVolume and backupName as part of the snapshotID which is returned from the csi CreateSnapshot call. this will be set as the `VolumeSnapshotContent.snapshotHandle` for the kubernetes created `VolumeSnapshotContent` object. We use the format `type://backupVolume/backupName` where the default type equals `bs` for direct references to longhorn backups. This is so that in the future we can refer to a custom kubernetes resource, which we can use for backup metadata persistence. For backup deletion all we have todo is decode the snapshotID then trigger the backup delete calls via the longhorn api. For the volume creation based on a CSI snapshot we can decode the snapshotID to lookup the backup in the backupstore. This will provide us with the backupURL which we can add to the `fromBackup` field in the longhorn created Volume resource. As part of prior work longhorn already knows how to restore these backups, this was initially used for a StorageClass parameter, by reusing the same mechanism we don't have to maintain multiple code paths for volume restoration. See examples of the necessary yaml manifests in the `User Experience In Detail` section. Creation test: create volume write data to volume create a `VolumeSnapshot` object wait for `VolumeSnapshot` to be ready to use check for backup existence on the backupstore Deletion test: create volume write data to volume create a `VolumeSnapshot` object wait for `VolumeSnapshot` to be ready to use check for backup existence on the backupstore delete `VolumeSnapshot` object wait for backup removal from the backupstore Restore csi snapshot test: create volume write data to volume create a `VolumeSnapshot` object wait for `VolumeSnapshot` to be ready to use check for backup existence on the backupstore create PVC with content source set to the `VolumeSnapshot` object wait for volume restoration verify restored volume data == previously written data Restore existing longhorn backup test: create volume write data to volume create a longhorn backup check for backup existence on the backupstore create a `VolumeSnapshotContent` object pointing to the longhorn backup create a `VolumeSnapshot` object pointing to the `VolumeSnapshotContent` object create PVC with content source set to the `VolumeSnapshot` object wait for volume restoration verify restored volume data == previously written data For csi snapshot support the user needs to update their kubernetes installation to at least 1.17 For environments where the user has pinned their csi images (airgap) the users need to manually provide the following images: longhornio/csi-provisioner:v1.6.0 longhornio/csi-snapshotter:v2.1.1 We upgraded the csi-provsioner from 1.4 to 1.6, which still supports kubernetes 1.13 as a minimum version Since we cannot assume that the users distribution has csi snapshotter support, the user needs to create a `VolumeSnapshotClass` to be able to use the csi snapshot support. Example longhorn `VolumeSnapshotClass` ```yaml kind: VolumeSnapshotClass apiVersion: snapshot.storage.k8s.io/v1beta1 metadata: name: longhorn driver: driver.longhorn.io deletionPolicy: Delete ``` The CRDs and snapshot controller installations are the responsibility of the Kubernetes distribution. See: https://kubernetes.io/docs/concepts/storage/volume-snapshots/#introduction We are discussing whether longhorn can provide these as part of the longhorn installation, but there isn't really a good way of making sure that there isn't a snapshot controller already deployed in the cluster. Make sure