Use NAS volumes with Flexvolume to share and persist data - File Storage NAS

You can use a File Storage NAS (NAS) file system to persist data and share the data among multiple pods. This topic describes how to use a NAS file system to persist and share data.

Prerequisites

Create an ACK managed cluster.
Obtain the kubeconfig file of a cluster and use kubectl to connect to the cluster.
A NAS file system is created in the NAS File System console. For more information, see Mount an NFS file system on a Linux ECS instance. The NAS file system and the cluster are deployed in the same zone.
A mount target is added to the NAS file system. For more information, see Manage mount targets. The NAS file system and the cluster are deployed in the same virtual private cloud (VPC).

Background information

If a NAS file system is mounted to multiple pods, the data in the file system is shared by the pods. In this case, the application must be able to synchronize data across these pods when data modifications are made by multiple pods.

Scenarios:

Your application requires high disk I/O.
You need a storage service that offers higher read and write throughput than Object Storage Service (OSS).
You want to share files across hosts. For example, you want to use a NAS file system as a file server.

Procedure

Create a NAS file system and a mount target.
Create a persistent volume (PV) and a persistent volume claim (PVC).

The following section describes how to create a PV and a PVC by using the FlexVolume plug-in provided by Alibaba Cloud and then mount a NAS file system.

Create a PV

Create a file named pv-nas.yaml.

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-nas
  labels:
    alicloud-pvname: pv-nas
spec:
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteMany
  flexVolume:
    driver: "alicloud/nas"
    options:
      server: "***-**.cn-hangzhou.nas.aliyuncs.com"   # Replace the value with the mount target. 
      path: "/k8s1"
      vers: "4.0"

Parameter	Description
`alicloud-pvname`	The name of the PV.
`server`	The mount target of the NAS file system. To obtain the mount target, log on to the NAS File System console. In the left-side navigation pane, click File System List, find the created file system, and then click Manage in the Actions column. On the page that appears, click Mount Targets. In the Mount Target section, copy the mount address in the IP Address of Mount Target column.
`path`	The mounted directory of the NAS file system. You can specify a subdirectory of a NAS file system. If no subdirectories exist, the system automatically creates a subdirectory.
`vers`	The version number of the Network File System (NFS) protocol. This parameter is optional. Valid values: 3 and 4.0. Default value: 3.
`mode`	The permissions to access the mounted directory. This parameter is optional. By default, this parameter is left empty. Note You are not allowed to grant permissions to access the root directory of a NAS file system. If you set the `mode` parameter for a NAS file system that stores a large amount of data, the process of mounting the NAS file system may be time-consuming or even fail. We recommend that you leave this parameter empty.

Run the following command to create the PV:
```
kubectl create -f pv-nas.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 its name 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

When you create a PVC of the NAS type, set the selector parameter to configure how to select a PV and bind it to the PVC.

Create a file named pvc-nas.yaml.

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

Run the following command to create the PVC:
```
kubectl create -f pvc-nas.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 its name 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 nas.yaml.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nas-static
  labels:
    app: nginx
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        ports:
        - containerPort: 80
        volumeMounts:
          - name: pvc-nas
            mountPath: "/data"
      volumes:
        - name: pvc-nas
          persistentVolumeClaim:
            claimName: pvc-nas

Run the following command to deploy an application:
```
kubectl create -f nas.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 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 sharing

Run the following command to query the application pods where the Deployment is running:

kubectl get pod

Expected output:

NAME                             READY   STATUS    RESTARTS   AGE
nas-static-f96b6b5d7-r****       1/1     Running   0          9m
nas-static-f96b6b5d7-w****       1/1     Running   0          9m

Run the following command to query files in the /data path:

kubectl exec nas-static-f96b6b5d7-r**** -- ls /data

Expected output:

kubectl exec nas-static-f96b6b5d7-w**** -- ls /data

Note

The output indicates that no file exists in the /data path.

Run the following command to create a file named nas in the /data path of a pod:
```
kubectl exec nas-static-f96b6b5d7-r**** -- touch /data/nas
```
Query files in the pods.
Run the following command to query files in the /data path of one pod:
```
kubectl exec nas-static-f96b6b5d7-r**** -- ls /data
```
Expected output:
```
nas
```
Run the following command to query files in the /data path of the other pod:
```
kubectl exec nas-static-f96b6b5d7-w**** -- ls /data
```
Expected output:
```
nas
```
Note
When you create a file in the /data path of one pod, you can also find the file in the /data path of the other pod. This indicates that data in the NAS file system is shared by the two pods.

Verify data persistence

Run the following command to delete all application pods:

kubectl delete pod nas-static-f96b6b5d7-r**** nas-static-f96b6b5d7-wthmb

Expected output:

pod "nas-static-f96b6b5d7-r****" deleted
pod "nas-static-f96b6b5d7-w****" deleted

Run the following command to view how the pods are deleted and recreated:

kubectl get pod -w -l app=nginx

Expected output:

NAME                             READY   STATUS              RESTARTS       AGE
nas-static-f96b6b5d7-r****       1/1     Running             0              27m
nas-static-f96b6b5d7-w****       1/1     Running             0              27m
nas-static-f96b6b5d7-r****       1/1     Terminating         0              28m
nas-static-f96b6b5d7-w****       0/1     Pending             0              0s
nas-static-f96b6b5d7-w****       0/1     Pending             0              0s
nas-static-f96b6b5d7-w****       0/1     ContainerCreating   0              0s
nas-static-f96b6b5d7-w****       1/1     Terminating         0              28m
nas-static-f96b6b5d7-n****       0/1     Pending             0              0s
nas-static-f96b6b5d7-n****       0/1     Pending             0              0s
nas-static-f96b6b5d7-n****       0/1     ContainerCreating   0              0s
nas-static-f96b6b5d7-r****       0/1     Terminating         0              28m
nas-static-f96b6b5d7-w****       0/1     Terminating         0              28m
nas-static-f96b6b5d7-r****       0/1     Terminating         0              28m
nas-static-f96b6b5d7-r****       0/1     Terminating         0              28m
nas-static-f96b6b5d7-w****       1/1     Running             0              10s
nas-static-f96b6b5d7-w****       0/1     Terminating         0              28m
nas-static-f96b6b5d7-w****       0/1     Terminating         0              28m
nas-static-f96b6b5d7-n****       1/1     Running             0              17s

Run the following command to query the name of the recreated pod:

kubectl get pod

Expected output:

NAME                             READY   STATUS    RESTARTS   AGE
nas-static-f96b6b5d7-n****       1/1     Running   0          21s
nas-static-f96b6b5d7-w****       1/1     Running   0          21s

Query files in the pods.
Run the following command to query files in the /data path of one pod:
```
kubectl exec nas-static-f96b6b5d7-n**** -- ls /data
```
Expected output:
```
nas
```
Run the following command to query files in the /data path of the other pod:
```
kubectl exec nas-static-f96b6b5d7-w**** -- ls /data
```
Expected output:
```
nas
```
Note
The nas file still exists. This indicates that data is persisted to the NAS volume.