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 dynamic creation of PVs through StorageClass. 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

Dynamically Mounting a Local PV on the Console

  1. Log in to the CCE console and click the cluster name to access the cluster console.

  2. Choose Workloads in the navigation pane. In the right pane, click the StatefulSets tab.

  3. 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.

  4. 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.

    (Optional) Storage Volume Name Prefix

    Available only when the cluster version is v1.23.14-r0, v1.25.9-r0, v1.27.6-r0, v1.28.4-r0, or later, and Everest of v2.4.15 or later is installed in the cluster.

    This parameter specifies the name of the underlying storage that is automatically created. The actual underlying storage name is in the format of "PV name prefix + PVC UID". If this parameter is left blank, the default prefix pvc will be used.

    For example, if the PV name prefix is set to test, the actual underlying storage name is test-{UID}.

    Capacity (GiB)

    Capacity of the requested storage volume.

    Access Mode

    Local PVs support only ReadWriteOnce, indicating that a PV 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.

  5. 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 specifies a 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, leading to 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 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.

  6. 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 Through kubectl

  1. Use kubectl to access the cluster.

  2. 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
            annotations:
              everest.io/csi.volume-name-prefix: test  # (Optional) PV name prefix of the automatically created underlying storage
          spec:
            accessModes:
              - ReadWriteOnce               # The value must be ReadWriteOnce for local PVs.
            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

    everest.io/csi.volume-name-prefix

    No

    (Optional) This parameter is available only when the cluster version is v1.23.14-r0, v1.25.9-r0, v1.27.6-r0, v1.28.4-r0, or later, and Everest of v2.4.15 or later is installed in the cluster.

    This parameter specifies the name of the underlying storage that is automatically created. The actual underlying storage name is in the format of "PV name prefix + PVC UID". If this parameter is left blank, the default prefix pvc will be used.

    Enter 1 to 26 characters that cannot start or end with a hyphen (-). Only lowercase letters, digits, and hyphens (-) are allowed.

    For example, if the PV name prefix is set to test, the actual underlying storage name is test-{UID}.

    storage

    Yes

    Requested capacity in the PVC, in Gi.

    storageClassName

    Yes

    The storage class of local PVs is csi-local-topology.

  3. 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

  1. View the deployed application and files.

    1. 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
      
    2. 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
      
    3. Run the following command to check the files in the /data path:

      kubectl exec statefulset-local-0 -- ls /data
      

      Expected output:

      lost+found
      
  2. Run the following command to create a file named static in the /data path:

    kubectl exec statefulset-local-0 --  touch /data/static
    
  3. Run the following command to check the files in the /data path:

    kubectl exec statefulset-local-0 -- ls /data
    

    Expected output:

    lost+found
    static
    
  4. 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
    
  5. 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
    

    The static file is retained, indicating that the data in the local PV can be stored persistently.