Use dynamically provisioned disks for stateful applications - Container Service for Kubernetes

This topic describes when and how to use dynamically provisioned disks for stateful applications.

Background information

When to use a dynamically provisioned disk:

If no disk is available when you deploy an application in a Container Service for Kubernetes (ACK) cluster, the system automatically creates a disk and uses it as a dynamic volume.

How to use a dynamically provisioned disk:

Manually create a persistent volume claim (PVC) and specify a StorageClass in the PVC.
When you deploy an application, the system automatically creates a persistent volume (PV) of the specified StorageClass.

Prerequisites

An ACK cluster is created. For more information, see Create an ACK managed cluster.
You are connected to the cluster through kubectl. For more information, see Step 2: Select a type of cluster credentials.
A provisioner is installed for the cluster. The provisioner can automatically create a disk of the specified StorageClass.

Provisioner

By default, a provisioner is automatically installed in each ACK cluster.

Create a StorageClass

By default, ACK creates four StorageClasses when the system is initialized. All of the StorageClasses use the default settings. Only single-zone clusters can use the four StorageClasses to dynamically provision disks. If your cluster is deployed in more than one zone, you must create new StorageClasses to mount disks as dynamic volumes. 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: a high-availability mode. In this mode, the system attempts to create an SSD. If SSD resources are exhausted, the system then attempts to create an ultra disk.

Create a storageclass.yaml file.

kind: StorageClass
apiVersion: storage.k8s.io/v1
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`	The value is set to alicloud/disk to automatically create a disk by using the provisioner.
`reclaimPolicy`	Specifies how the disk is handled after the corresponding PVC is deleted. 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 disk. Valid values: cloud, cloud_efficiency, cloud_ssd, and available.
`regionId`	The ID of the region to which the disk belongs. The value must be set to the region ID of the cluster. This parameter is optional.
`zoneId`	The ID of the zone to which the disk belongs. This parameter is optional. If your cluster is deployed in one zone, set the value to the ID of the zone. If your cluster is deployed in multiple zones, set the value to the IDs of the zones. Example: `zoneid: cn-hangzhou-a,cn-hangzhou-b,cn-hangzhou-c`
`fstype`	The file system of the disk. This parameter is optional. 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

Create a 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
```

On the details page of the cluster, click Volumes and choose Persistent Volume Claims in the left-side navigation pane. On the Persistent Volume Claims page, you can view the created PVC and the PV that is bound to the PVC. The StorageClass of the PVC is alicloud-disk-ssd-hangzhou-b.

Create a Deployment

Create a 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 a Deployment:
```
kubectl create -f nginx-dynamic.yaml
```

On the details page of the cluster, click Workloads and choose Deployments in the left-side navigation pane. On the Deployments page, you can view the created Deployment.

Use the disk for persistent storage

Run the following command to query the pod that hosts the Deployment:
```
kubectl get pod | grep dynamic
```
The following output is returned:
```
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 output is returned:

/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 output is returned:
```
lost+found
```
Run the following command to create the dynamic file 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 output is returned:
```
dynamic
lost+found
```
Run the following command to delete the pod nginx-dynamic-5c74594ccb-zl9pf:
```
kubectl delete pod nginx-dynamic-5c74594ccb-zl9pf
```
The following output is returned:
```
pod "nginx-dynamic-5c74594ccb-zl9pf" deleted
```

Open another kubectl command-line interface (CLI) and run the following command to query how the pod is deleted and recreated:

kubectl get pod -w -l app=nginx

The following output is returned:

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 name of the recreated pod:

kubectl get pod

The following output is returned:

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

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