Use a static cloud disk when creating a stateful service

Edit in Github

Last Updated: Jan 07, 2019 Edit in Github

This topic describes typical scenarios in which a static cloud disk is needed for creating a stateful service, and the procedure for how to use one.

Scenarios and method

Scenarios for using cloud disks:

You want to create applications that demand high disk I/O performance and do not require shared data. For example, MySQL, Redis, and other data storage services.
You want logs to be written at high speed.
You want your stored data to exist persistently. That is, the data still exist when the life cycle of the pod ends.

Scenario for using static cloud disks:

You have purchased a cloud disk.

Method of using static cloud disks:

Manually create a Persistent Volume (PV) and a Persistent Volume Claim (PVC).

Prerequisites

You have created a Kubernetes cluster. For more information, see Create a Kubernetes cluster.
You have created a cloud disk. For more information, see Create a cloud disk.
You have connected to the Kubernetes cluster by using kubectl, see Connect to a Kubernetes cluster by using kubectl.

Limits

Cloud disks are the non-shared storage devices provided by the Alibaba Cloud Storage Team. Each cloud disk can be mounted to only one pod.
In a Kubernetes cluster, a cloud disk can be mounted only to a node that resides in the same zone as the cloud disk.

Create a PV

Create a pv-static.yaml file.
```
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>: indicates the PV name. This parameter must be set to the same value as that of the volumeID parameter, namely, the cloud disk ID.
- failure-domain.beta.kubernetes.io/zone: <your-zone>: indicates the zone in which the cloud disk resides. For example, cn-hangzhou-b.
- failure-domain.beta.kubernetes.io/region: <your-region>: indicates the region in which the cloud disk resides. For example, cn-hangzhou.
If you use a Kubernetes cluster that has multiple zones, you must set the failure-domain.beta.kubernetes.io/zone parameter and the failure-domain.beta.kubernetes.io/region parameter so that you can guarantee that your pod can be scheduled to the zone in which the cloud disk resides.
Run the following command to create a PV:
```
$ kubectl create -f pv-static.yaml
```

Result

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

Create a PVC

Create a PVC for the cloud disk. Specifically, you need to set theselector field to filter for the created PV so that you can associate the PVC with the correct PV.

Create a pvc-static.yaml file.

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
```

Result

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

Create an application

Create a static.yaml file.

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 create a deployment:
```
$ kubectl create -f static.yaml
```

Result

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

Persistent data storage on the static cloud disk

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

$ kubectl get pod | grep static
nginx-static-78c7dcb9d7-g9lll   2/2     Running     0          32s

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

$ kubectl exec nginx-static-78c7dcb9d7-g9lll df | grep data
/dev/vdf        20511312    45080  20449848   1% /data

Run the following command to view the file in the /data path:

$ kubectl exec nginx-static-78c7dcb9d7-g9lll ls /data
lost+found

Run the following command to create a file named static in the /data path:
```
$ kubectl exec nginx-static-78c7dcb9d7-g9lll touch /data/static
```

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

$ kubectl exec nginx-static-78c7dcb9d7-g9lll ls /data
static
lost+found

Run the following command to remove the pod named nginx-static-78c7dcb9d7-g9lll:

$ kubectl delete pod nginx-static-78c7dcb9d7-g9lll
pod "nginx-static-78c7dcb9d7-g9lll" deleted

Open another kubectl interface and run the following command to view the process in which the preceding pod is removed and a new pod is created by Kubernetes:

$ kubectl get pod -w -l app=nginx
NAME                            READY   STATUS    RESTARTS   AGE
nginx-static-78c7dcb9d7-g9lll   2/2     Running   0          50s
nginx-static-78c7dcb9d7-g9lll   2/2   Terminating   0     72s
nginx-static-78c7dcb9d7-h6brd   0/2   Pending   0     0s
nginx-static-78c7dcb9d7-h6brd   0/2   Pending   0     0s
nginx-static-78c7dcb9d7-h6brd   0/2   Init:0/1   0     0s
nginx-static-78c7dcb9d7-g9lll   0/2   Terminating   0     73s
nginx-static-78c7dcb9d7-h6brd   0/2   Init:0/1   0     5s
nginx-static-78c7dcb9d7-g9lll   0/2   Terminating   0     78s
nginx-static-78c7dcb9d7-g9lll   0/2   Terminating   0     78s
nginx-static-78c7dcb9d7-h6brd   0/2   PodInitializing   0     6s
nginx-static-78c7dcb9d7-h6brd   2/2   Running   0     8sg   0     8s

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

$ kubectl get pod
NAME                            READY   STATUS      RESTARTS   AGE
nginx-static-78c7dcb9d7-h6brd   2/2     Running     0          14s

Run the following command to verify that the created file named static in the /data path has not been removed, indicating that data in the static cloud disk can be stored persistently:
```
$ kubectl exec nginx-static-78c7dcb9d7-h6brd ls /data
static
lost+found
```