Updated on 2024-01-26 GMT+08:00

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

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. In the navigation pane on the left, click Workloads. 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 (VTC).
  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.

    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.

  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 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, errors will occur in containers. 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.
    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 a subpath, for example, tmp, indicating that data in the mount path of the container will be stored in the tmp folder of the volume.

    A subpath is used to mount a local volume so that the same data volume is used in a single pod. 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 is not 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.

(kubectl) Using an Existing Local PV

  1. Use kubectl to connect to 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
          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.

  3. Run the following command to create an application 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 view 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 view 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

    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.

  1. Choose Storage from the navigation pane, and click the PersistentVolumeClaims (PVCs) or PersistentVolumes (PVs) tab.
  2. 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.

  1. Choose Storage from the navigation pane, and click the PersistentVolumeClaims (PVCs) or PersistentVolumes (PVs) tab.
  2. Click View YAML in the Operation column of the target PVC or PV to view or download the YAML.