Dynamically Mounting a Local PV to a StatefulSet¶

Application Scenarios¶

Dynamic mounting is available only for creating a StatefulSet. It is implemented through a volume claim template (volumeClaimTemplates field) and depends on the storage class to dynamically provision PVs. In this mode, each pod in a multi-pod StatefulSet is associated with a unique PVC and PV. After a pod is rescheduled, the original data can still be mounted to it based on the PVC name. In the common mounting mode for a Deployment, if ReadWriteMany is supported, multiple pods of the Deployment will be mounted to the same underlying storage.

Prerequisites¶

You have created a cluster and installed the CSI add-on (Everest) in the cluster.
If you want to create a cluster using commands, use kubectl to connect to the cluster. For details, see Connecting to a Cluster Using kubectl.
You have imported a data disk of a node to the local PV storage pool. For details, see Importing a PV to a Storage Pool.

Dynamically Mounting a Local PV on the Console¶

Log in to the CCE console and click the cluster name to access the cluster console.
In the navigation pane on the left, click Workloads. In the right pane, click the StatefulSets tab.
Click Create Workload in the upper right corner. On the displayed page, click Data Storage in the Container Settings area and click Add Volume to select VolumeClaimTemplate (VTC).

Click Create PVC. In the dialog box displayed, configure the volume claim template parameters.

Click Create.

Parameter	Description
PVC Type	In this section, select Local PV.
PVC Name	Enter the name of the PVC. After a PVC is created, a suffix is automatically added based on the number of pods. The format is <Custom PVC name>-<Serial number>, for example, example-0.
Creation Method	You can only select Dynamically provision to create a PVC, PV, and underlying storage on the console in cascading mode.
Storage Classes	The storage class of local PVs is csi-local-topology.
Access Mode	Local PVs support only ReadWriteOnce, indicating that a storage volume can be mounted to one node in read/write mode. For details, see Volume Access Modes.
Storage Pool	View the imported storage pool. For details about how to import a new data volume to the storage pool, see Importing a PV to a Storage Pool.
Capacity (GiB)	Capacity of the requested storage volume.

Enter the path to which the volume is mounted.

**Table 1** Mounting a storage volume¶
Parameter	Description
Mount Path	Enter a mount path, for example, /tmp. This parameter indicates the container path to which a data volume will be mounted. Do not mount the volume to a system directory such as / or /var/run. Otherwise, containers will be malfunctional. Mount the volume to an empty directory. If the directory is not empty, ensure that there are no files that affect container startup. Otherwise, the files will be replaced, causing container startup failures or workload creation failures. Important NOTICE: If a volume is mounted to a high-risk directory, use an account with minimum permissions to start the container. Otherwise, high-risk files on the host machine may be damaged.
Subpath	Enter the subpath of the storage volume and mount a path in the storage volume to the container. In this way, different folders of the same storage volume can be used in a single pod. tmp, for example, indicates that data in the mount path of the container is stored in the tmp folder of the storage volume. If this parameter is left blank, the root path is used by default.
Permission	Read-only: You can only read the data in the mounted volumes. Read/Write: You can modify the data volumes mounted to the path. Newly written data will not be migrated if the container is migrated, which may cause data loss.

In this example, the disk is mounted to the /data path of the container. The container data generated in this path is stored in the local PV.

Dynamically mount and use storage volumes. For details about other parameters, see Creating a StatefulSet. After the configuration, click Create Workload.
After the workload is created, the data in the container mount directory will be persistently stored. Verify the storage by referring to Verifying Data Persistence.

Dynamically Mounting a Local PV Using kubectl¶

Use kubectl to connect to the cluster.

Create a file named statefulset-local.yaml. In this example, the local PV is mounted to the /data path.

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: statefulset-local
  namespace: default
spec:
  selector:
    matchLabels:
      app: statefulset-local
  template:
    metadata:
      labels:
        app: statefulset-local
    spec:
      containers:
        - name: container-1
          image: nginx:latest
          volumeMounts:
            - name: pvc-local          # The value must be the same as that in the volumeClaimTemplates field.
              mountPath: /data         # Location where the storage volume is mounted.
      imagePullSecrets:
        - name: default-secret
  serviceName: statefulset-local       # Headless Service name.
  replicas: 2
  volumeClaimTemplates:
    - apiVersion: v1
      kind: PersistentVolumeClaim
      metadata:
        name: pvc-local
        namespace: default
      spec:
        accessModes:
          - ReadWriteOnce               # The local PV must adopt ReadWriteOnce.
        resources:
          requests:
            storage: 10Gi               # Storage volume capacity.
        storageClassName: csi-local-topology      # StorageClass is local PV.
---
apiVersion: v1
kind: Service
metadata:
  name: statefulset-local   # Headless Service name.
  namespace: default
  labels:
    app: statefulset-local
spec:
  selector:
    app: statefulset-local
  clusterIP: None
  ports:
    - name: statefulset-local
      targetPort: 80
      nodePort: 0
      port: 80
      protocol: TCP
  type: ClusterIP

**Table 2** Key parameters¶
Parameter	Mandatory	Description
storage	Yes	Requested capacity in the PVC, in Gi.
storageClassName	Yes	The storage class of local PVs is csi-local-topology.

Run the following command to create a workload to which the local PV is mounted:
```
kubectl apply -f statefulset-local.yaml
```
After the workload is created, you can try Verifying Data Persistence.

Verifying Data Persistence¶

View the deployed application and files.

Run the following command to view the created pod:

kubectl get pod | grep statefulset-local

Expected output:

statefulset-local-0          1/1     Running   0             45s
statefulset-local-1          1/1     Running   0             28s

Run the following command to check whether the local PV has been mounted to the /data path:

kubectl exec statefulset-local-0 -- df | grep data

Expected output:

/dev/mapper/vg--everest--localvolume--persistent-pvc-local              10255636     36888  10202364   0% /data

Run the following command to view the files in the /data path:
```
kubectl exec statefulset-local-0 -- ls /data
```
Expected output:
```
lost+found
```

Run the following command to create a file named static in the /data path:
```
kubectl exec statefulset-local-0 --  touch /data/static
```
Run the following command to view the files in the /data path:
```
kubectl exec statefulset-local-0 -- ls /data
```
Expected output:
```
lost+found
static
```
Run the following command to delete the pod named web-local-auto-0:
```
kubectl delete pod statefulset-local-0
```
Expected output:
```
pod "statefulset-local-0" deleted
```
After the deletion, the StatefulSet controller automatically creates a replica with the same name. Run the following command to check whether the files in the /data path have been modified:
```
kubectl exec statefulset-local-0 -- ls /data
```
Expected output:
```
lost+found
static
```
If the static file still exists, the data in the local PV can be stored persistently.

Related Operations¶

You can also perform the operations listed in Table 3.

**Table 3** Related operations¶
Operation	Description	Procedure
Viewing events	You can view event names, event types, number of occurrences, Kubernetes events, first occurrence time, and last occurrence time of the PVC or PV.	Choose Storage in the navigation pane and click the PersistentVolumeClaims (PVCs) or PersistentVolumes (PVs) tab. Click View Events in the Operation column of the target PVC or PV to view events generated within one hour (event data is retained for one hour).
Viewing a YAML file	You can view, copy, and download the YAML files of a PVC or PV.	Choose Storage in the navigation pane and click the PersistentVolumeClaims (PVCs) or PersistentVolumes (PVs) tab. Click View YAML in the Operation column of the target PVC or PV to view or download the YAML.

last updated: 2024-05-19 01:43