Use OSS 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 an Object Storage Service (OSS) volume to persist data.

Background information

OSS is a secure, cost-effective, and highly reliable cloud storage service provided by Alibaba Cloud. You can mount an OSS volume on multiple pods of a Container Service for Kubernetes (ACK) cluster.

Scenarios

Average requirements on disk I/O
Sharing of data, including configuration files, images, and small video files

Procedure

Create an OSS bucket.
Obtain an AccessKey ID and AccessKey secret.
Create a persistent volume (PV) and a persistent volume claim (PVC).

Prerequisites

Create an ACK managed cluster.
Obtain the kubeconfig file of a cluster and use kubectl to connect to the cluster.
An OSS bucket is created in the OSS console. For more information, see Create buckets.

Precautions

kubelet and the OSSFS driver may be restarted when the ACK cluster is upgraded. As a result, the mounted OSS directory becomes unavailable. In this case, you must recreate the pods on which the OSS volume is mounted. You can add health check settings in the YAML file to restart the pods and remount the OSS volume when the OSS directory becomes unavailable.
If your ACK cluster is of the latest Kubernetes version, the preceding issue is fixed.

Create a PV

Create a file named pv-oss.yaml.
```
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-oss
  labels:
    alicloud-pvname: pv-oss
spec:
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteMany
  storageClassName: oss
  flexVolume:
    driver: "alicloud/oss"
    options:
      bucket: "docker"                        //Replace the value with the bucket name. 
      path: /path                             //Replace the value with the relative path of the sub directory.
      url: "oss-cn-hangzhou.aliyuncs.com"     //Replace the value with the endpoint of the OSS bucket. 
      akId: "***"                             //Replace the value with the AccessKey ID. 
      akSecret: "***"                         //Replace the value with the AccessKey secret. 
      otherOpts: "-o max_stat_cache_size=0 -o allow_other"   //Replace the value with custom parameter values. 
```
Parameter description
- alicloud-pvname: the name of the PV. This value must be used in the selector field of the PVC that is associated with the PV.
- bucket: the name of the OSS bucket. Only OSS buckets can be mounted to the ACK cluster. You cannot mount the subdirectories or files in an OSS bucket to the ACK cluster.
- path: the path relative to the root directory of the OSS bucket to be mounted. The default value is /. This parameter is supported by csi-plugin 1.14.8.32-c77e277b-aliyun and later.
- url: the endpoint of the OSS bucket. For more information, see Regions and endpoints. To obtain the endpoint, log on to the OSS console. In the left-side navigation pane, find the OSS bucket that you want to manage. On the Overview page, find the Domain Names section and view the endpoint of the OSS bucket in the Endpoint column.
- akId: the AccessKey ID. Log on to the ACK console, move the pointer over the icon in the upper-right corner of the page and select AccessKey Management from the shortcut menu. On the page that appears, create an AccessKey ID and an AccessKey secret.
- akSecret: the AccessKey secret. To obtain the AccessKey secret, perform the steps described in akId.
- otherOpts: the custom parameters that are used to mount the OSS bucket. The parameters must be in the following format: -o *** -o ***.
Run the following command to create a PV:
```
kubectl create -f pv-oss.yaml
```

Expected result

Log on to the ACK console.
In the left-side navigation pane, click Clusters.
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.
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 PVC of the OSS type. Set the selector parameter to configure how to select the PV to which the PVC is bound. Set the storageClassName parameter to bind the PVC with the PV of the OSS type.

Create a file named pvc-oss.yaml.

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: pvc-oss
spec:
  accessModes:
    - ReadWriteMany
  storageClassName: oss
  resources:
    requests:
      storage: 5Gi
  selector:
    matchLabels:
      alicloud-pvname: pv-oss

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

Expected result

Log on to the ACK console.
In the left-side navigation pane, click Clusters.
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.
In the left-side navigation pane of the details page, choose Volumes > Persistent Volume Claims. Verify that the newly created PVC is displayed.

Create an application

Create a file named oss-static.yaml.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: oss-static
  labels:
    app: nginx
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        ports:
        - containerPort: 80
        volumeMounts:
          - name: pvc-oss
            mountPath: "/data"
          - name: pvc-oss
            mountPath: "/data1"
        livenessProbe:
          exec:
            command:
            - sh
            - -c
            - cd /data
          initialDelaySeconds: 30
          periodSeconds: 30
      volumes:
        - name: pvc-oss
          persistentVolumeClaim:
            claimName: pvc-oss

Note

For more information about how to set livenessProbe to configure health checks, see OSS volume overview.

Run the following command to deploy an application:
```
kubectl create -f oss-static.yaml d
```

Expected result

Log on to the ACK console.
In the left-side navigation pane, click Clusters.
On the Clusters page, find the cluster that you want to manage, and click the name of the cluster or click Applications in the Actions column.
In the left-side navigation pane of the cluster details page, choose Workloads > Deployments. Verify that the newly created application is displayed.

Verify data persistence

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

kubectl get pod

Expected output:

NAME                             READY   STATUS    RESTARTS   AGE
oss-static-66fbb85b67-dqbl2      1/1     Running   0          1h

Run the following command to query the files in the /data path:
```
kubectl exec oss-static-66fbb85b67-dqbl2 -- ls /data | grep tmpfile
```
Note
The output indicates that no file exists in the /data path.
Run the following command to create a file named tmpfile in the /data path:
```
kubectl exec oss-static-66fbb85b67-dqbl2 -- touch /data/tmpfile
```
Run the following command to query the files in the /data path:
```
kubectl exec oss-static-66fbb85b67-dqbl2 -- ls /data | grep tmpfile
```
Expected output:
```
tmpfile
```
Run the following command to delete the pod named oss-static-66fbb85b67-dqbl2:
```
kubectl delete pod oss-static-66fbb85b67-dqbl2
```
Expected output:
```
pod "oss-static-66fbb85b67-dqbl2" 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
oss-static-66fbb85b67-dqbl2   1/1     Running           0          78m
oss-static-66fbb85b67-dqbl2   1/1     Terminating       0          78m
oss-static-66fbb85b67-zlvmw   0/1     Pending           0          <invalid>
oss-static-66fbb85b67-zlvmw   0/1     Pending           0          <invalid>
oss-static-66fbb85b67-zlvmw   0/1     ContainerCreating 0          <invalid>
oss-static-66fbb85b67-dqbl2   0/1     Terminating       0          78m
oss-static-66fbb85b67-dqbl2   0/1     Terminating       0          78m
oss-static-66fbb85b67-dqbl2   0/1     Terminating       0          78m
oss-static-66fbb85b67-zlvmw   1/1     Running           0          <invalid>

Run the following command to query the recreated pod:

kubectl get pod

Expected output:

NAME                             READY   STATUS    RESTARTS   AGE
oss-static-66fbb85b67-zlvmw      1/1     Running   0          40s

Run the following command to verify that the tmpfile file exists in the /data path. This indicates that data is persisted to the OSS volume.
```
kubectl exec oss-static-66fbb85b67-zlvmw -- ls /data | grep tmpfile
```
Expected output:
```
tmpfile
```