Add a blog for volume group snapshots beta
Xing Yang
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layout: blog
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title: "Kubernetes 1.32: Moving Volume Group Snapshots to Beta"
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date: 2024-12-11
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slug: kubernetes-1-32-volume-group-snapshot-beta
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draft: true
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author: >
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Xing Yang (VMware by Broadcom)
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---
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Volume group snapshots were [introduced](/blog/2023/05/08/kubernetes-1-27-volume-group-snapshot-alpha/)
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as an Alpha feature with the Kubernetes 1.27 release.
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The recent release of Kubernetes v1.32 moved that support to **beta**.
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The support for volume group snapshots relies on a set of
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[extension APIs for group snapshots](https://kubernetes-csi.github.io/docs/group-snapshot-restore-feature.html#volume-group-snapshot-apis).
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These APIs allow users to take crash consistent snapshots for a set of volumes.
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Behind the scenes, Kubernetes uses a label selector to group multiple PersistentVolumeClaims
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for snapshotting.
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A key aim is to allow you restore that set of snapshots to new volumes and
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recover your workload based on a crash consistent recovery point.
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This new feature is only supported for [CSI](https://kubernetes-csi.github.io/docs/) volume drivers.
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## An overview of volume group snapshots
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Some storage systems provide the ability to create a crash consistent snapshot of
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multiple volumes. A group snapshot represents _copies_ made from multiple volumes, that
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are taken at the same point-in-time. A group snapshot can be used either to rehydrate
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new volumes (pre-populated with the snapshot data) or to restore existing volumes to
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a previous state (represented by the snapshots).
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## Why add volume group snapshots to Kubernetes?
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The Kubernetes volume plugin system already provides a powerful abstraction that
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automates the provisioning, attaching, mounting, resizing, and snapshotting of block
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and file storage.
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Underpinning all these features is the Kubernetes goal of workload portability:
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Kubernetes aims to create an abstraction layer between distributed applications and
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underlying clusters so that applications can be agnostic to the specifics of the
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cluster they run on and application deployment requires no cluster specific knowledge.
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There was already a [VolumeSnapshot](/docs/concepts/storage/volume-snapshots/) API
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that provides the ability to take a snapshot of a persistent volume to protect against
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data loss or data corruption. However, there are other snapshotting functionalities
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not covered by the VolumeSnapshot API.
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Some storage systems support consistent group snapshots that allow a snapshot to be
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taken from multiple volumes at the same point-in-time to achieve write order consistency.
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This can be useful for applications that contain multiple volumes. For example,
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an application may have data stored in one volume and logs stored in another volume.
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If snapshots for the data volume and the logs volume are taken at different times,
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the application will not be consistent and will not function properly if it is restored
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from those snapshots when a disaster strikes.
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It is true that you can quiesce the application first, take an individual snapshot from
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each volume that is part of the application one after the other, and then unquiesce the
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application after all the individual snapshots are taken. This way, you would get
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application consistent snapshots.
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However, sometimes the application quiesce can be so time consuming that you want to do it less frequently,
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or it may not be possible to quiesce an application at all.
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For example, a user may want to run weekly backups with application quiesce
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and nightly backups without application quiesce but with consistent group support which
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provides crash consistency across all volumes in the group.
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## Kubernetes APIs for volume group snapshots
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Kubernetes' support for _volume group snapshots_ relies on three API kinds that
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are used
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for managing snapshots:
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VolumeGroupSnapshot
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: Created by a Kubernetes user (or perhaps by your own automation) to request
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creation of a volume group snapshot for multiple persistent volume claims.
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It contains information about the volume group snapshot operation such as the
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timestamp when the volume group snapshot was taken and whether it is ready to use.
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The creation and deletion of this object represents a desire to create or delete a
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cluster resource (a group snapshot).
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VolumeGroupSnapshotContent
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: Created by the snapshot controller for a dynamically created VolumeGroupSnapshot.
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It contains information about the volume group snapshot including the volume group
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snapshot ID.
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This object represents a provisioned resource on the cluster (a group snapshot).
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The VolumeGroupSnapshotContent object binds to the VolumeGroupSnapshot for which it
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was created with a one-to-one mapping.
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VolumeGroupSnapshotClass
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: Created by cluster administrators to describe how volume group snapshots should be
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created, including the driver information, the deletion policy, etc.
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These three API kinds are defined as
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[CustomResourceDefinitions](/docs/concepts/extend-kubernetes/api-extension/custom-resources/)
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(CRDs).
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These CRDs must be installed in a Kubernetes cluster for a CSI Driver to support
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volume group snapshots.
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## What components are needed to support volume group snapshots
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Volume group snapshots are implemented in the
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[external-snapshotter](https://github.com/kubernetes-csi/external-snapshotter) repository.
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Implementing volume group snapshots meant adding or changing several components:
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* Added new CustomResourceDefinitions for VolumeGroupSnapshot and two supporting APIs.
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* Volume group snapshot controller logic is added to the common snapshot controller.
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* Adding logic to make CSI calls into the snapshotter sidecar controller.
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The volume snapshot controller and CRDs are deployed once per
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cluster, while the sidecar is bundled with each CSI driver.
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Therefore, it makes sense to deploy the volume snapshot controller and CRDs as a cluster addon.
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The Kubernetes project recommends that Kubernetes distributors
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bundle and deploy the volume snapshot controller and CRDs as part
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of their Kubernetes cluster management process (independent of any CSI Driver).
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## What's new in Beta?
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* The VolumeGroupSnapshot feature in CSI spec moved to GA in the [v1.11.0 release](https://github.com/container-storage-interface/spec/releases/tag/v1.11.0).
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* The snapshot validation webhook was deprecated in external-snapshotter v8.0.0 and it is now removed.
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Most of the validation webhook logic was added as validation rules into the CRDs.
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Minimum required Kubernetes version is 1.25 for these validation rules.
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One thing in the validation webhook not moved to CRDs is the prevention of creating
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multiple default volume snapshot classes and multiple default volume group snapshot classes
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for the same CSI driver.
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With the removal of the validation webhook, an error will still be raised when dynamically
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provisioning a VolumeSnapshot or VolumeGroupSnapshot when multiple default volume snapshot
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classes or multiple default volume group snapshot classes for the same CSI driver exist.
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* The `enable-volumegroup-snapshot` flag in the snapshot-controller and the CSI snapshotter
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sidecar has been replaced by a feature gate.
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Since VolumeGroupSnapshot is a new API, the feature moves to Beta but the feature gate is
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disabled by default.
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To use this feature, enable the feature gate by adding the flag `--feature-gates=CSIVolumeGroupSnapshot=true`
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when starting the snapshot-controller and the CSI snapshotter sidecar.
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* The logic to dynamically create the VolumeGroupSnapshot and its corresponding individual
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VolumeSnapshot and VolumeSnapshotContent objects are moved from the CSI snapshotter to the common
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snapshot-controller.
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New RBAC rules are added to the common snapshot-controller and some RBAC rules are removed from
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the CSI snapshotter sidecar accordingly.
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## How do I use Kubernetes volume group snapshots
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### Creating a new group snapshot with Kubernetes
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Once a VolumeGroupSnapshotClass object is defined and you have volumes you want to
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snapshot together, you may request a new group snapshot by creating a VolumeGroupSnapshot
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object.
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The source of the group snapshot specifies whether the underlying group snapshot
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should be dynamically created or if a pre-existing VolumeGroupSnapshotContent
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should be used.
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A pre-existing VolumeGroupSnapshotContent is created by a cluster administrator.
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It contains the details of the real volume group snapshot on the storage system which
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is available for use by cluster users.
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One of the following members in the source of the group snapshot must be set.
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* `selector` - a label query over PersistentVolumeClaims that are to be grouped
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together for snapshotting. This selector will be used to match the label
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added to a PVC.
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* `volumeGroupSnapshotContentName` - specifies the name of a pre-existing
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VolumeGroupSnapshotContent object representing an existing volume group snapshot.
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#### Dynamically provision a group snapshot
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In the following example, there are two PVCs.
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```console
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NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS VOLUMEATTRIBUTESCLASS AGE
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pvc-0 Bound pvc-6e1f7d34-a5c5-4548-b104-01e72c72b9f2 100Mi RWO csi-hostpath-sc <unset> 2m15s
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pvc-1 Bound pvc-abc640b3-2cc1-4c56-ad0c-4f0f0e636efa 100Mi RWO csi-hostpath-sc <unset> 2m7s
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```
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Label the PVCs.
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```console
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% kubectl label pvc pvc-0 group=myGroup
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persistentvolumeclaim/pvc-0 labeled
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% kubectl label pvc pvc-1 group=myGroup
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persistentvolumeclaim/pvc-1 labeled
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```
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For dynamic provisioning, a selector must be set so that the snapshot controller can find PVCs
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with the matching labels to be snapshotted together.
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```yaml
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apiVersion: groupsnapshot.storage.k8s.io/v1beta1
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kind: VolumeGroupSnapshot
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metadata:
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name: snapshot-daily-20241217
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namespace: demo-namespace
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spec:
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volumeGroupSnapshotClassName: csi-groupSnapclass
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source:
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selector:
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matchLabels:
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group: myGroup
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```
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In the VolumeGroupSnapshot spec, a user can specify the VolumeGroupSnapshotClass which
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has the information about which CSI driver should be used for creating the group snapshot.
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A VolumGroupSnapshotClass is required for dynamic provisioning.
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```yaml
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apiVersion: groupsnapshot.storage.k8s.io/v1beta1
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kind: VolumeGroupSnapshotClass
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metadata:
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name: csi-groupSnapclass
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annotations:
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kubernetes.io/description: "Example group snapshot class"
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driver: example.csi.k8s.io
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deletionPolicy: Delete
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```
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As a result of the volume group snapshot creation, a corresponding VolumeGroupSnapshotContent
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object will be created with a volumeGroupSnapshotHandle pointing to a resource on the storage
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system.
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Two individual volume snapshots will be created as part of the volume group snapshot creation.
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```console
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NAME READYTOUSE SOURCEPVC RESTORESIZE SNAPSHOTCONTENT AGE
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snapshot-0962a745b2bf930bb385b7b50c9b08af471f1a16780726de19429dd9c94eaca0 true pvc-0 100Mi snapcontent-0962a745b2bf930bb385b7b50c9b08af471f1a16780726de19429dd9c94eaca0 16m
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snapshot-da577d76bd2106c410616b346b2e72440f6ec7b12a75156263b989192b78caff true pvc-1 100Mi snapcontent-da577d76bd2106c410616b346b2e72440f6ec7b12a75156263b989192b78caff 16m
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```
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#### Importing an existing group snapshot with Kubernetes
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To import a pre-existing volume group snapshot into Kubernetes, you must also import
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the corresponding individual volume snapshots.
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Identify the individual volume snapshot handles, manually construct a
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VolumeSnapshotContent object first, then create a VolumeSnapshot object pointing to
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the VolumeSnapshotContent object. Repeat this for every individual volume snapshot.
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Then manually create a VolumeGroupSnapshotContent object, specifying the
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volumeGroupSnapshotHandle and individual volumeSnapshotHandles already existing
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on the storage system.
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```yaml
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apiVersion: groupsnapshot.storage.k8s.io/v1beta1
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kind: VolumeGroupSnapshotContent
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metadata:
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name: static-group-content
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spec:
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deletionPolicy: Delete
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driver: hostpath.csi.k8s.io
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source:
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groupSnapshotHandles:
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volumeGroupSnapshotHandle: e8779136-a93e-11ef-9549-66940726f2fd
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volumeSnapshotHandles:
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- e8779147-a93e-11ef-9549-66940726f2fd
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- e8783cd0-a93e-11ef-9549-66940726f2fd
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volumeGroupSnapshotRef:
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name: static-group-snapshot
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namespace: demo-namespace
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```
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After that create a VolumeGroupSnapshot object pointing to the VolumeGroupSnapshotContent
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object.
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```yaml
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apiVersion: groupsnapshot.storage.k8s.io/v1beta1
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kind: VolumeGroupSnapshot
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metadata:
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name: static-group-snapshot
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namespace: demo-namespace
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spec:
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source:
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volumeGroupSnapshotContentName: static-group-content
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```
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### How to use group snapshot for restore in Kubernetes
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At restore time, the user can request a new PersistentVolumeClaim to be created from
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a VolumeSnapshot object that is part of a VolumeGroupSnapshot. This will trigger
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provisioning of a new volume that is pre-populated with data from the specified
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snapshot. The user should repeat this until all volumes are created from all the
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snapshots that are part of a group snapshot.
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```yaml
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apiVersion: v1
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kind: PersistentVolumeClaim
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metadata:
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name: examplepvc-restored-2024-12-17
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namespace: demo-namespace
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spec:
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storageClassName: example-foo-nearline
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dataSource:
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name: snapshot-0962a745b2bf930bb385b7b50c9b08af471f1a16780726de19429dd9c94eaca0
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kind: VolumeSnapshot
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apiGroup: snapshot.storage.k8s.io
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accessModes:
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- ReadWriteOncePod
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resources:
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requests:
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storage: 100Mi # must be enough storage to fit the existing snapshot
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```
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## As a storage vendor, how do I add support for group snapshots to my CSI driver?
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To implement the volume group snapshot feature, a CSI driver **must**:
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* Implement a new group controller service.
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* Implement group controller RPCs: `CreateVolumeGroupSnapshot`, `DeleteVolumeGroupSnapshot`, and `GetVolumeGroupSnapshot`.
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* Add group controller capability `CREATE_DELETE_GET_VOLUME_GROUP_SNAPSHOT`.
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See the [CSI spec](https://github.com/container-storage-interface/spec/blob/master/spec.md)
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and the [Kubernetes-CSI Driver Developer Guide](https://kubernetes-csi.github.io/docs/)
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for more details.
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As mentioned earlier, it is strongly recommended that Kubernetes distributors
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bundle and deploy the volume snapshot controller and CRDs as part
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of their Kubernetes cluster management process (independent of any CSI Driver).
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As part of this recommended deployment process, the Kubernetes team provides a number of
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sidecar (helper) containers, including the
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[external-snapshotter sidecar container](https://kubernetes-csi.github.io/docs/external-snapshotter.html)
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which has been updated to support volume group snapshot.
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The external-snapshotter watches the Kubernetes API server for
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VolumeGroupSnapshotContent objects, and triggers `CreateVolumeGroupSnapshot` and
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`DeleteVolumeGroupSnapshot` operations against a CSI endpoint.
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## What are the limitations?
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The beta implementation of volume group snapshots for Kubernetes has the following limitations:
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* Does not support reverting an existing PVC to an earlier state represented by
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a snapshot (only supports provisioning a new volume from a snapshot).
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* No application consistency guarantees beyond any guarantees provided by the storage system
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(e.g. crash consistency). See this [doc](https://github.com/kubernetes/community/blob/30d06f49fba22273f31b3c616b74cf8745c19b3d/wg-data-protection/data-protection-workflows-white-paper.md#quiesce-and-unquiesce-hooks)
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for more discussions on application consistency.
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## What’s next?
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Depending on feedback and adoption, the Kubernetes project plans to push the volume
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group snapshot implementation to general availability (GA) in a future release.
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## How can I learn more?
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- The [design spec](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/3476-volume-group-snapshot)
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for the volume group snapshot feature.
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- The [code repository](https://github.com/kubernetes-csi/external-snapshotter) for volume group
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snapshot APIs and controller.
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- CSI [documentation](https://kubernetes-csi.github.io/docs/) on the group snapshot feature.
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## How do I get involved?
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This project, like all of Kubernetes, is the result of hard work by many contributors
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from diverse backgrounds working together. On behalf of SIG Storage, I would like to
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offer a huge thank you to the contributors who stepped up these last few quarters
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to help the project reach beta:
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* Ben Swartzlander ([bswartz](https://github.com/bswartz))
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* Cici Huang ([cici37](https://github.com/cici37))
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* Hemant Kumar ([gnufied](https://github.com/gnufied))
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* James Defelice ([jdef](https://github.com/jdef))
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* Jan Šafránek ([jsafrane](https://github.com/jsafrane))
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* Madhu Rajanna ([Madhu-1](https://github.com/Madhu-1))
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* Manish M Yathnalli ([manishym](https://github.com/manishym))
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* Michelle Au ([msau42](https://github.com/msau42))
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* Niels de Vos ([nixpanic](https://github.com/nixpanic))
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* Leonardo Cecchi ([leonardoce](https://github.com/leonardoce))
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* Rakshith R ([Rakshith-R](https://github.com/Rakshith-R))
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* Raunak Shah ([RaunakShah](https://github.com/RaunakShah))
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* Saad Ali ([saad-ali](https://github.com/saad-ali))
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* Xing Yang ([xing-yang](https://github.com/xing-yang))
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* Yati Padia ([yati1998](https://github.com/yati1998))
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For those interested in getting involved with the design and development of CSI or
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any part of the Kubernetes Storage system, join the
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[Kubernetes Storage Special Interest Group](https://github.com/kubernetes/community/tree/master/sig-storage) (SIG).
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We always welcome new contributors.
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We also hold regular [Data Protection Working Group meetings](https://github.com/kubernetes/community/tree/master/wg-data-protection).
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New attendees are welcome to join our discussions.
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