Use volume snapshots created from disks - User Guide for Kubernetes Clusters| Alibaba Cloud Documentation Center

Container Service for Kubernetes (ACK) allows you to create volume snapshots from disks and use the volume snapshots to restore application data. This topic describes the basic terms related to volume snapshots and how to use volume snapshots in ACK clusters. This topic also describes how to dynamically and statically create volume snapshots.

Prerequisites

ACK clusters that use Kubernetes V1.18 and later support volume snapshots. To use volume snapshots that are created from disks, make sure that Kubernetes V1.18 or later is used in your ACK cluster. For more information, see Create an ACK managed cluster.
Log on the Elastic Compute Service (ECS) console and select the region where your cluster is deployed. Make sure that the volume snapshot feature is enabled. For more information, see Activate ECS Snapshot.

Background information

When you deploy stateful applications in an ACK cluster, disks are commonly used to store application data. You can create snapshots from disks and use these snapshots to restore application data. ACK also allows you to use snapshots to back up and restore data. You can back up and restore data in your ACK cluster in the following ways:

Create backups (volume snapshots) from disks by using VolumeSnapshots.
Restore data by setting dataSource to the related persistent volume claim (PVC).

Instruction

To enable volume snapshots, you can use CustomResourceDefinitions (CRDs) in ACK to define the following resources:


Resource name	Description
VolumeSnapshotContent	A snapshot that is created from a volume in the ACK cluster. It is created and managed by administrators. A VolumeSnapshotContent does not belong to any namespace. A VolumeSnapshotContent is a cluster resource similar to a persistent volume (PV).
VolumeSnapshot	A request for a volume snapshot. It is created and managed by users. A VolumeSnapshot belongs to a specific namespace. A VolumeSnapshot is a cluster resource similar to a PVC.
VolumeSnapshotClass	Specifies the attributes of a VolumeSnapshot, such as the parameters and controllers that are used to create snapshots. A VolumeSnapshotClass is a cluster resource similar to a StorageClass.

To use volume snapshots, you must associate these resources with each other based on the following rules:

Before you can use volume snapshots, associate a VolumeSnapshot with a VolumeSnapshotContent in the same way that you associate a PV with a PVC.
After you specify a valid value in the VolumeSnapshotClassName field for a VolumeSnapshot, the ACK cluster automatically creates a VolumeSnapshotContent for the VolumeSnapshot. If you specify an invalid value or do not specify a value in the VolumeSnapshotClassName field, the VolumeSnapshotContent cannot be automatically created. In this case, you must manually create a VolumeSnapshotContent and associate the VolumeSnapshotContent with the VolumeSnapshot.
Each VolumeSnapshotContent can be associated with only one VolumeSnapshot.

Notice When you delete a VolumeSnapshotContent, the associated snapshot is also deleted.

Dynamically create a volume snapshot

The following figure shows the procedure to dynamically create a volume snapshot from the disk that is used in an ACK cluster.

The following table describes the steps that are performed in the procedure.


Step	Description
①	Create an application and create a disk volume to store application data.
②	Create a VolumeSnapshot. Then, the ACK cluster automatically creates a VolumeSnapshotContent and a volume snapshot.
3	Create another application, create a PVC for the application, and then specify the volume snapshot that is created in Step 2 as the source of the PVC.

The preceding steps are performed to enable the following features:

Backup: Snapshot 1 is created to back up data in Volume 1.
Restoration: Snapshot 1 is used to restore data in Volume 1 to Volume 2.

The following example shows how to create an NGINX application and restore the data of the application by using a volume snapshot. The following procedure demonstrates how to use a volume snapshot to restore the data of an application.

Create a VolumeSnapshotClass.

Create a volumesnapshotclass.yaml file and copy the following content to the file:

apiVersion: snapshot.storage.k8s.io/v1beta1
kind: VolumeSnapshotClass
metadata:
  name: default-snapclass
driver: diskplugin.csi.alibabacloud.com
parameters:
   snapshotType: "xxx"
   instantAccessRetentionDays: "1"
deletionPolicy: Delete


Parameter	Description
deletionPolicy	If the value is set to `Delete`, the corresponding VolumeSnapshotContent and snapshot are deleted when you delete a VolumeSnapshot. If the value is set to `Retain`, the corresponding VolumeSnapshotContent and snapshot are retained when you delete a VolumeSnapshot.
parameters.snapshotType	If the value is set to `InstantAccess`, the instant access mode is enabled to dynamically create snapshots. This feature is applicable to only enhanced SSDs. For more information, see Enable or disable the instant access feature. The default value is `normal`, which indicates that a normal snapshot is created.
parameters.instantAccessRetentionDays	You must set this parameter if parameters.snapshotType is set to InstantAccess. This parameter specifies the retention period of snapshot that is created in instant access mode. After the feature is disabled, the snapshot that is created in instant access mode is converted to a normal snapshot.

Run the following command to create a VolumeSnapshotClass:
```
kubectl apply -f volumesnapshotclass.yaml
```

Create an application and write data to the application.

Create an nginx.yaml file and copy the following content to the file:

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  selector:
    matchLabels:
      app: nginx
  serviceName: "nginx"
  replicas: 1
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        volumeMounts:
        - name: disk-ssd
          mountPath: /data
  volumeClaimTemplates:
  - metadata:
      name: disk-ssd
    spec:
      accessModes: [ "ReadWriteOnce" ]
      storageClassName: "alicloud-disk-ssd"
      resources:
        requests:
          storage: 20Gi

Run the following command to create an NGINX application:
```
kubectl apply -f nginx.yaml
```

Run the following command to write data to pod web-0:

kubectl exec -it web-0 touch /data/test
kubectl exec -it web-0 ls /data

The following output is returned:

lost+found test

Create a VolumeSnapshot.

Create a snapshot.yaml file and copy the following content to the file:

apiVersion: snapshot.storage.k8s.io/v1beta1
kind: VolumeSnapshot
metadata:
  name: new-snapshot-demo
  namespace: default
spec:
  volumeSnapshotClassName: default-snapclass
  source:
    persistentVolumeClaimName: disk-ssd-web-0

Run the following command to create a VolumeSnapshot:
```
kubectl apply -f snapshot.yaml
```
Run the following command to check whether the VolumeSnapshot and VolumeSnapshotContent are created. You can also log on to the ECS console to view the snapshot.
Run the following command to view the VolumeSnapshot:
```
kubectl get volumesnapshots.snapshot.storage.k8s.io
```
The following output is returned:
```
NAME                                            AGE
new-snapshot-demo                                36m
```
Run the following command to view the VolumeSnapshotContent:
```
kubectl get VolumeSnapshotContent
```
The following output is returned:
```
NAME                                            AGE
snapshotcontent-222222                           36m
```

Restore data.

Create an nginx-restore file and copy the following content to the file:

apiVersion: v1
kind: Service
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: nginx
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web-restore
spec:
  selector:
    matchLabels:
      app: nginx
  serviceName: "nginx"
  replicas: 1
  template:
    metadata:
      labels:
        app: nginx
    spec:
      hostNetwork: true
      containers:
      - name: nginx
        image: nginx
        command: ["sh", "-c"]
        args: ["sleep 10000"]
        volumeMounts:
        - name: disk-ssd
          mountPath: /data
  volumeClaimTemplates:
  - metadata:
      name: disk-ssd
    spec:
      accessModes: [ "ReadWriteOnce" ]
      storageClassName: alicloud-disk-ssd
      resources:
        requests:
          storage: 20Gi
      dataSource:
        name: new-snapshot-demo
        kind: VolumeSnapshot
        apiGroup: snapshot.storage.k8s.io

Note In the dataSource field of the volumeClaimTemplates section, set kind to VolumeSnapshot and set name to new-snapshot-demo. The new-snapshot-demo snapshot is created in Step 3.

Run the following command to restore the application data:
```
kubectl apply -f nginx-restore.yaml
```

Run the following command to view the application data in pod web-restore-0:
```
kubectl exec -it web-restore-0 ls /data
```
The following output is returned:
```
lost+found test
```
The output shows that the same application data is returned. This indicates that the application data is restored.

Statically create a volume snapshot (import an existing snapshot from an ECS instance)

The following procedure demonstrates how to import an existing snapshot from an ECS instance to an ACK cluster.

Use the following YAML template to create a VolumeSnapshotContent:

apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotContent
metadata:
  name: new-snapshot-content-test
spec:
  deletionPolicy: Retain
  driver: diskplugin.csi.alibabacloud.com
  source:
    snapshotHandle: <your-snapshotid>
  volumeSnapshotRef:
    name: new-snapshot-demo
    namespace: default


Parameter	Description
snapshotHandle	Enter the snapshot ID that is generated on the ECS instance page.
volumeSnapshotRef	Enter the following information for the VolumeSnapshot that you want to create: name: the name of the VolumeSnapshot. namespace: the namespace to which the VolumeSnapshot belongs.

Use the following YAML template to create a VolumeSnapshot:

apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  name: new-snapshot-demo
  namespace: default
spec:
  source:
    volumeSnapshotContentName: new-snapshot-content-test


Parameter	Description
metadata.name	The name of the VolumeSnapshot. The name must be the same as the VolumeSnapshot name that is specified in the preceding VolumeSnapshotContent.
spec.source.volumeSnapshotContentName	The name of the VolumeSnapshotContent that is associated with the VolumeSnapshot. The name must be the same as the name of the VolumeSnapshotContent that is created in the preceding step.

Restore data.

Create an nginx-restore file and copy the following content to the file:

apiVersion: v1
kind: Service
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: nginx
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web-restore
spec:
  selector:
    matchLabels:
      app: nginx
  serviceName: "nginx"
  replicas: 1
  template:
    metadata:
      labels:
        app: nginx
    spec:
      hostNetwork: true
      containers:
      - name: nginx
        image: nginx
        command: ["sh", "-c"]
        args: ["sleep 10000"]
        volumeMounts:
        - name: disk-ssd
          mountPath: /data
  volumeClaimTemplates:
  - metadata:
      name: disk-ssd
    spec:
      accessModes: [ "ReadWriteOnce" ]
      storageClassName: alicloud-disk-ssd
      resources:
        requests:
          storage: 20Gi
      dataSource:
        name: new-snapshot-demo
        kind: VolumeSnapshot
        apiGroup: snapshot.storage.k8s.io

Note In the dataSource field of the volumeClaimTemplates section, set kind to VolumeSnapshot and set name to new-snapshot-demo. The new-snapshot-demo snapshot is created in Step 2.

Run the following command to restore the application data:
```
kubectl apply -f nginx-restore.yaml
```

Run the following command to view the application data in pod web-restore-0:
```
kubectl exec -it web-restore-0 ls /data
```
The following output is returned:
```
lost+found test
```
The output shows that the same application data is returned. This indicates that the application data is restored.