Use a NAS file system when creating a stateful service - Best Practices| Alibaba Cloud Documentation Center

This topic describes typical scenarios in which a NAS file system is needed for creating a stateful service, and the procedure for how to use one.

Scenarios and method

If a NAS file system is mounted to multiple pods, the pods share the data in the NAS file system. After a pod modifies the data stored in the NAS file system, the application supported by the pods is required to automatically update the modified data for the other pods.

Scenarios for using a NAS file system

You want to create or run applications that demand high disk I/O performance.
You need a storage service that has higher read and write performance than OSS.
You want to share files across hosts. For example, you want to use a NAS file system as a file server.

Method of using a NAS file system:

Manually create a NAS file system and add a mount point to it.
Manually create a PV and a PVC.

This topic describes how to use Alibaba Cloud NAS services in the PV/ PVC mode by using the flexvolume plugin provided by Alibaba Cloud.

Prerequisites

You have created a Kubernetes cluster. For more information, see Create a Kubernetes cluster.
You have connected to the Kubernetes cluster by using kubectl, see Connect to a Kubernetes cluster by using kubectl.
You have created a NAS file system in the NAS console. For more information, see Create a file system. You must make sure that the NAS file system and your Kubernetes cluster are in the same zone.
You have added a mount point for your Kubernetes cluster in the created NAS file system. For information, see Add a mount point. You must make sure that the NAS file system and your cluster are in the same VPC.

Create a PV

Create a pv-nas.yaml file.
```
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 this value with your mount point.
      path: "/k8s1"
      vers: "4.0"
```
Parameter description
- alicloud-pvname: indicates a PV name.
- server: indicates a NAS mount point. To view your mount point, log on to the NAS console, click File System List in the left-side navigation pane, select the target file system, and click Manage in the Action column to view the Mount Address in the Mount Point area. The mount address is the mount point of your NAS file system.
- path: indicates the NAS mount directory. You can mount a NAS sub-directory to your cluster. If the NAS sub-directory specified by you does not exist, the system automatically creates the NAS sub-directory and mounts it to your cluster.
- vers: (optional) indicates the version number of the NFS mount protocol. NFS file system V3.0 and V4.0 are available. The default is V4.0.
- mode: (optional) indicates the access permission to the mount directory. By default, this parameter is not set.
  Note
  - Access permission to the root directory of the NAS file system cannot be set.
  - 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 to a cluster may take an excessive amount of time or even fail. We recommend that you do not set this parameter.
Run the following command to create a PV:
```
$ kubectl create -f pv-nas.yaml
```

Result

In the left-side navigation pane under Kubernetes, choose Clusters > Volumes, and select the target cluster to view the created PV.

Create a PVC

Create a PVC for the NAS file system. Specifically, you need to set the selector field to filter for the created PV so that you can associate the PVC with the correct PV.

Create a pvc-nas.yaml file.

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 a PVC:
```
$ kubectl create -f pvc-nas.yaml
```

Result

In the left-side navigation pane under Kubernetes, choose Application > Volumes Claim, and select the target cluster and namespace to view the created PVC.

Create an application

Create a 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 create a deployment:
```
$ kubectl create -f nas.yaml
```

Result

In the left-side navigation pane under Kubernetes, choose Application > Deployment, and select the target cluster and namespace to view the created deployment.

Verify that the NAS file system is shared by pods

Run the following command to view the pods in which the created deployment resides:

$ kubectl get pod
NAME                             READY   STATUS    RESTARTS   AGE
nas-static-f96b6b5d7-rcb2f       1/1     Running   0          9m
nas-static-f96b6b5d7-wthmb       1/1     Running   0          9m

Run the following commands to view the files in the /data path of each pod:
```
$ kubectl exec nas-static-f96b6b5d7-rcb2f ls /data
```
```
$ kubectl exec nas-static-f96b6b5d7-wthmb ls /data
```
Note The two /data paths are empty.
Run the following command to create file nas in the /data path of one pod:
```
$ kubectl exec nas-static-f96b6b5d7-rcb2f touch /data/nas
```
Run the following commands to view the files in the /data path of each pod:
```
$ kubectl exec nas-static-f96b6b5d7-rcb2f ls /data
nas
```
```
$ kubectl exec nas-static-f96b6b5d7-wthmb ls /data
nas
```
Note After you create the file in the /data path of one pod, the file then exists in both the /data paths of the two pods. This means that the two pods share the NSA file system.

Verify that data on the NAS file system are stored persistently

Run the following command to remove all the pods of the created application:

$ kubectl delete pod nas-static-f96b6b5d7-rcb2f nas-static-f96b6b5d7-wthmb
pod "nas-static-f96b6b5d7-rcb2f" deleted
pod "nas-static-f96b6b5d7-wthmb" deleted

Open another kubectl interface and run the following command to view the process in which the original pods are removed and new pods are created by Kubernetes:

$ kubectl get pod -w -l app=nginx
NAME                             READY   STATUS    RESTARTS   AGE
nas-static-f96b6b5d7-rcb2f       1/1     Running   0          27m
nas-static-f96b6b5d7-wthmb       1/1     Running   0          27m
nas-static-f96b6b5d7-rcb2f   1/1   Terminating   0     28m
nas-static-f96b6b5d7-wnqdj   0/1   Pending   0     0s
nas-static-f96b6b5d7-wnqdj   0/1   Pending   0     0s
nas-static-f96b6b5d7-wnqdj   0/1   ContainerCreating   0     0s
nas-static-f96b6b5d7-wthmb   1/1   Terminating   0     28m
nas-static-f96b6b5d7-nwkds   0/1   Pending   0     0s
nas-static-f96b6b5d7-nwkds   0/1   Pending   0     0s
nas-static-f96b6b5d7-nwkds   0/1   ContainerCreating   0     0s
nas-static-f96b6b5d7-rcb2f   0/1   Terminating   0     28m
nas-static-f96b6b5d7-wthmb   0/1   Terminating   0     28m
nas-static-f96b6b5d7-rcb2f   0/1   Terminating   0     28m
nas-static-f96b6b5d7-rcb2f   0/1   Terminating   0     28m
nas-static-f96b6b5d7-wnqdj   1/1   Running   0     10s
nas-static-f96b6b5d7-wthmb   0/1   Terminating   0     28m
nas-static-f96b6b5d7-wthmb   0/1   Terminating   0     28m
nas-static-f96b6b5d7-nwkds   1/1   Running   0     17s

Run the following command to view the new pods created by Kubernetes:

$ kubectl get pod
NAME                             READY   STATUS    RESTARTS   AGE
nas-static-f96b6b5d7-nwkds       1/1     Running   0          21s
nas-static-f96b6b5d7-wnqdj       1/1     Running   0          21s

Run the following commands to view the files in the /data path of each pod:
```
$ kubectl exec nas-static-f96b6b5d7-nwkds ls /data 
nas
```
```
$ kubectl exec nas-static-f96b6b5d7-wnqdj ls /data
nas
```
Note The created file, namely, file nas has not been removed. This means that data in the NAS file system can be stored persistently.