Use statically provisioned disk volumes for persistent storage - Container Service for Kubernetes

When a node that hosts running containers fails, stateful applications may lose the business data stored in the containers. This issue can be resolved by using persistent storage. This topic describes how to use a statically provisioned disk volume to persist data.

Prerequisites

Before you start, make sure that you have performed the following operations:

Background information

Scenarios

Provide storage space for applications that require high disk I/O and do not require data sharing. For example, storage services such as MySQL and Redis.
Write log data at high speeds.
Store data in a way that is independent of the lifetime of a pod.

You must create a disk before you can statically provision a disk volume.

You must manually create a persistent volume (PV) and a persistent volume claim (PVC) to use a statically provisioned disk volume. For more information, see Mount a statically provisioned disk volume.

Limits

The disks provided by Alibaba Cloud cannot be shared. Each disk can be mounted only to one pod.
A disk can be mounted only to a node that is deployed in the same zone as the disk.

Create a PV

Create a file named pv-static.yaml.
```
apiVersion: v1
kind: PersistentVolume
metadata:
  name: <your-disk-id>
  labels:
    alicloud-pvname: <your-disk-id>
    failure-domain.beta.kubernetes.io/zone: <your-zone>
    failure-domain.beta.kubernetes.io/region: <your-region>
spec:
  capacity:
    storage: 20Gi
  accessModes:
    - ReadWriteOnce
  flexVolume:
    driver: "alicloud/disk"
    fsType: "ext4"
    options:
      volumeId: "<your-disk-id>"
```
Note
- alicloud-pvname: <your-disk-id>: the name of the PV. Set the value to the disk ID.
- failure-domain.beta.kubernetes.io/zone: <your-zone>: the zone where the disk is deployed. Example: cn-hangzhou-b.
- failure-domain.beta.kubernetes.io/region: <your-region>: the region where the disk is deployed. Example: cn-hangzhou.
If your cluster is deployed across zones, you must specify failure-domain.beta.kubernetes.io/zone and failure-domain.beta.kubernetes.io/region. This ensures that your pods are scheduled to the zone where the disk is deployed.
Run the following command to create a PV:
```
kubectl create -f pv-static.yaml
```
Verify the result
1. Log on to the ACK console.
2. In the left-side navigation pane, click Clusters.
3. On the Clusters page, find the cluster that you want to manage, and click the name of the cluster or click Details in the Actions column.
4. In the left-side navigation pane of the details page, choose Volumes > Persistent Volumes. Verify that the newly created PV is displayed.

Create a PVC

Create a file named pvc-static.yaml.

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: pvc-disk
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 20Gi
  selector:
    matchLabels:
      alicloud-pvname: <your-disk-id>

Run the following command to create a PVC:
```
kubectl create -f pvc-static.yaml
```
View the result
1. Log on to the ACK console.
2. In the left-side navigation pane, click Clusters.
3. On the Clusters page, find the cluster that you want to manage, and click the name of the cluster or click Details in the Actions column.
4. In the left-side navigation pane of the details page, choose Volumes > Persistent Volume Claims.
5. On the Persistent Volume Claims page, verify that the newly created PVC is displayed.

Create an application

Create a file named static.yaml.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-static
  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: pvc-disk

Run the following command to deploy an application that uses the statically provisioned disk volume:
```
kubectl create -f static.yaml
```
View the result
1. Log on to the ACK console.
2. In the left-side navigation pane, click Clusters.
3. On the Clusters page, find the cluster that you want to manage, and click the name of the cluster or click Details in the Actions column.
4. In the left-side navigation pane of the details page, choose Workloads > Deployments.
5. On the Deployments page, verify that the newly created application is displayed.

Verify data persistence

Run the following command to query the pods that host the application:

kubectl get pod | grep static

Expected output:

nginx-static-78c7dcb9d7-g****   2/2     Running     0          32s

Run the following command to check whether a new disk is mounted to the /data path:

kubectl exec nginx-static-78c7dcb9d7-g**** -- df | grep data

Expected output:

/dev/vdf        20511312    45080  20449848   1% /data

Run the following command to query the files in the /data path:
```
kubectl exec nginx-static-78c7dcb9d7-g**** -- ls /data
```
Expected output:
```
lost+found
```
Run the following command to create a file named static in the /data path:
```
kubectl exec nginx-static-78c7dcb9d7-g**** -- touch /data/static
```
Run the following command to query the files in the /data path:
```
kubectl exec nginx-static-78c7dcb9d7-g**** -- ls /data
```
Expected output:
```
static
lost+found
```
Run the following command to delete the pod named nginx-static-78c7dcb9d7-g****.
```
kubectl delete pod nginx-static-78c7dcb9d7-g****
```
Expected output:
```
pod "nginx-static-78c7dcb9d7-g****" deleted
```

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

kubectl get pod -w -l app=nginx

Expected output:

NAME                            READY   STATUS            RESTARTS   AGE
nginx-static-78c7dcb9d7-g****   2/2     Running           0          50s
nginx-static-78c7dcb9d7-g****   2/2     Terminating       0          72s
nginx-static-78c7dcb9d7-h****   0/2     Pending           0          0s
nginx-static-78c7dcb9d7-h****   0/2     Pending           0          0s
nginx-static-78c7dcb9d7-h****   0/2     Init:0/1          0          0s
nginx-static-78c7dcb9d7-g****   0/2     Terminating       0          73s
nginx-static-78c7dcb9d7-h****   0/2     Init:0/1          0          5s
nginx-static-78c7dcb9d7-g****   0/2     Terminating       0          78s
nginx-static-78c7dcb9d7-g****   0/2     Terminating       0          78s
nginx-static-78c7dcb9d7-h****   0/2     PodInitializing   0          6s
nginx-static-78c7dcb9d7-h****   2/2     Running           0          8s

Run the following command to query the recreated pod:

kubectl get pod

Expected output:

NAME                            READY   STATUS      RESTARTS   AGE
nginx-static-78c7dcb9d7-h****   2/2     Running     0          14s

Run the following command to verify that the static file still exists in the /data path. This indicates that data is persisted to the disk.
```
kubectl exec nginx-static-78c7dcb9d7-h6brd -- ls /data
```
Expected output:
```
static
lost+found
```