Use dynamic disks to create PVs for stateful services - Best Practices| Alibaba Cloud Documentation Center

Background

When to use dynamic disks:

You have not purchased disks. When you deploy an application, the system automatically purchases a disk.

How to use dynamic disks:

Create a persistent volume claim (PVC) and specify the StorageClass in the PVC.
When you deploy an application, the system automatically creates a PV based on the StorageClass.

Prerequisites

A Container Service for Kubernetes (ACK) cluster is created. For more information, see Create a cluster of ACK Managed Edition.
The cluster is connected through kubectl. For more information, see Use kubectl to connect to a cluster.
A provisioner is installed for the cluster. The provisioner can automatically create a disk based on the StorageClass.

Install a provisioner

By default, a provisioner is automatically installed during cluster creation.

Create a StorageClass

By default, a cluster has four StorageClasses. Each StorageClass uses the default settings. The four StorageClasses apply to a cluster where nodes are deployed in the same zone. If a cluster has nodes running across multiple zones, you must create a StorageClass. The following list describes the four StorageClasses:

alicloud-disk-common: creates a basic disk.
alicloud-disk-efficiency: creates an ultra disk.
alicloud-disk-ssd: creates an SSD.
alicloud-disk-available: This option ensures high availability. The system attempts to create an ultra disk first. If no ultra disk is available in the specified zone, the system attempts to create an SSD. If no SSD is available, the system attempts to create a basic disk.

Add the following content to the storageclass.yaml file:

kind: StorageClass
apiVersion: storage.k8s.io/v1beta1
metadata:
  name: alicloud-disk-ssd-hangzhou-b
provisioner: alicloud/disk
reclaimPolicy: Retain
parameters:
  type: cloud_ssd
  regionid: cn-hangzhou
  zoneid: cn-hangzhou-b
  fstype: "ext4"
  readonly: "false"


Parameter	Description
`provisioner`	Automatically creates a disk for the cluster. Set the value to alicloud/disk.
`reclaimPolicy`	The policy for reclaiming the disk. Valid values: Delete and Retain. Default value: Delete. Note If you set the value to Delete, the disk is automatically deleted when you delete the PVC. The disk data cannot be restored.
`type`	The type of the disk. Valid values: cloud, cloud_efficiency, cloud_ssd, and available.
`regionid`	Optional. The ID of the region to which the disk belongs. Set the value to the region ID of the cluster.
`zoneid`	Optional. The ID of the zone to which the disk belongs. If all nodes in the cluster are running in the same zone, set the value to the zone ID of the cluster. If the cluster has nodes running across multiple zones, specify multiple zone IDs based on the following example. `zoneid: cn-hangzhou-a,cn-hangzhou-b,cn-hangzhou-c`
`fstype`	Optional. The type of the disk file system. Default value: ext4.
`readonly`	Specifies whether the disk is read-only. This parameter is optional. Valid values: true and false. true: The disk is read-only. false: You can perform read and write operations on the disk. Default value: false.
`encrypted`	Specifies whether to encrypt the disk. This parameter is optional. Valid values: true and false. true: encrypts the disk. false: does not encrypt the disk. Default value: false.

Run the following command to create a StorageClass:
```
kubectl create -f storageclass.yaml
```

Create a PVC

Add the following content to the pvc-ssd.yaml file:

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: disk-ssd
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: alicloud-disk-ssd-hangzhou-b
  resources:
    requests:
      storage: 20Gi

Run the following command to create a PVC:
```
kubectl create -f pvc-ssd.yaml
```

In the left-side navigation pane of the management page of the cluster, click Persistent Volumes. On the Persistent Volume Claims tab, you can view the PVC. The StorageClass of the PVC is alicloud-disk-ssd-hangzhou-b, and the specified PV is bound to the PVC.

Create an application

Add the following content to the pvc-dynamic.yaml file:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-dynamic
  labels:
    app: nginx
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        volumeMounts:
          - name: disk-pvc
            mountPath: "/data"
      volumes:
        - name: disk-pvc
          persistentVolumeClaim:
            claimName: disk-ssd

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

In the left-side navigation pane of the details page of the cluster, click Workload. On the Deployments tab, view the application.

Use dynamic disks for persistent storage

Run the following command to query the pod that runs the application:
```
kubectl get pod | grep dynamic
```
The following command output appears:
```
nginx-dynamic-5c74594ccb-zl9pf     2/2     Running     0          3m
```
Run the following command to check whether a new disk is mounted to the /data path:
```
kubectl exec nginx-dynamic-5c74594ccb-zl9pf df | grep data
```
The following command output appears:
```
/dev/vdh        20511312    45080  20449848   1% /data
```
Run the following command to query the files in the /data path:
```
kubectl exec nginx-dynamic-5c74594ccb-zl9pf ls /data
```
The following command output appears:
```
lost+found
```

Run the following command to create file dynamic in the /data path:

kubectl exec nginx-dynamic-5c74594ccb-zl9pf touch /data/dynamic

Run the following command to query the files in the /data path:
```
kubectl exec nginx-dynamic-5c74594ccb-zl9pf ls /data
```
The following command output appears:
```
dynamic
lost+found
```
Run the following command to delete pod nginx-dynamic-5c74594ccb-zl9pf:
```
kubectl delete pod nginx-dynamic-5c74594ccb-zl9pf
```
The following command output appears:
```
pod "nginx-dynamic-5c74594ccb-zl9pf" deleted
```

Open another kubectl CLI and run the following command to query how the pod is deleted and a new pod is created:

kubectl get pod -w -l app=nginx

The following command output appears:

NAME                               READY   STATUS    RESTARTS   AGE
nginx-dynamic-5c74594ccb-zl9pf     2/2     Running   0          6m48s
nginx-dynamic-5c74594ccb-zl9pf   2/2   Terminating   0     7m32s
nginx-dynamic-5c74594ccb-45sd4   0/2   Pending   0     0s
nginx-dynamic-5c74594ccb-45sd4   0/2   Pending   0     0s
nginx-dynamic-5c74594ccb-45sd4   0/2   Init:0/1   0     0s
nginx-dynamic-5c74594ccb-zl9pf   0/2   Terminating   0     7m32s
nginx-dynamic-5c74594ccb-zl9pf   0/2   Terminating   0     7m33s
nginx-dynamic-5c74594ccb-zl9pf   0/2   Terminating   0     7m33s
nginx-dynamic-5c74594ccb-45sd4   0/2   PodInitializing   0     5s
nginx-dynamic-5c74594ccb-45sd4   2/2   Running   0     22s

Run the following command to query the new pod:

kubectl get pod

The following command output appears:

NAME                               READY   STATUS      RESTARTS   AGE
nginx-dynamic-5c74594ccb-45sd4     2/2     Running     0          2m

Run the following command to verify that file dynamic in the /data path is not deleted. This indicates that data in the dynamic disk is persistently stored.
```
kubectl exec nginx-dynamic-5c74594ccb-45sd4 ls /data
```
The following command output appears:
```
dynamic
lost+found
```