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

You have created a cluster and installed the CCE Container Storage (Everest) add-on in the cluster.
To create a cluster using commands, ensure kubectl is used. For details, see Connecting to a Cluster Using kubectl.

Dynamically Mounting an EVS Disk on the Console

Log in to the CCE console and click the cluster name to access the cluster console.
Choose Workloads in the navigation pane. 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.

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

Click Create.

Parameter	Description
PVC Type	In this example, select EVS.
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 select Dynamically provision to create a PVC, PV, and underlying storage on the console in cascading mode.
Storage Classes	The storage class for EVS disks is csi-disk.
(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}.
AZ	Select the AZ of the EVS disk. The AZ must be the same as that of the cluster node. NOTE: An EVS disk can only be mounted to a node in the same AZ. After an EVS disk is created, its AZ cannot be changed.
Disk Type	Select an EVS disk type. EVS disk types vary depending on regions. Obtain the available EVS types on the console.
Capacity (GiB)	Capacity of the requested storage volume.
Access Mode	EVS volumes support only ReadWriteOnce, indicating that a storage volume can be mounted to one node in read/write mode. For details, see Volume Access Modes.
Encryption	Configure whether to encrypt underlying storage. If you select Enabled (key), an encryption key must be configured. Before using encryption, check whether the region where the EVS disk is located supports disk encryption.
Resource Tag	You can add resource tags to classify resources, which is supported only when the Everest version in the cluster is 2.1.39 or later. You can create predefined tags on the TMS console. The predefined tags are available to all resources that support tags. You can use predefined tags to improve the tag creation and resource migration efficiency. CCE automatically creates system tags CCE-Cluster-ID={Cluster ID}, CCE-Cluster-Name={Cluster name}, and CCE-Namespace={Namespace name}. These tags cannot be modified. NOTE: After a dynamic PV of the EVS type is created, the resource tags cannot be updated on the CCE console. To update these resource tags, go to the EVS console.

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. 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 EVS disk.

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 an EVS Volume Through kubectl

Use kubectl to access the cluster.

Create a file named statefulset-evs.yaml. In this example, the EVS volume is mounted to the /data path.

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: statefulset-evs
  namespace: default
spec:
  selector:
    matchLabels:
      app: statefulset-evs
  template:
    metadata:
      labels:
        app: statefulset-evs
    spec:
      containers:
        - name: container-1
          image: nginx:latest
          volumeMounts:
            - name: pvc-disk           # 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-evs         # Headless Service name
  replicas: 2
  volumeClaimTemplates:
    - apiVersion: v1
      kind: PersistentVolumeClaim
      metadata:
        name: pvc-disk
        namespace: default
        annotations:
          everest.io/disk-volume-type: SAS    # EVS disk type
          everest.io/crypt-key-id: <your_key_id>    # (Optional) Encryption key ID. Mandatory for an encrypted disk.

          everest.io/disk-volume-tags: '{"key1":"value1","key2":"value2"}' # (Optional) Custom resource tags
          csi.storage.k8s.io/fstype: xfs    # (Optional) The file system is of the xfs type. If it is left blank, ext4 will be used by default.
          everest.io/csi.volume-name-prefix: test  # (Optional) PV name prefix of the automatically created underlying storage
        labels:
          failure-domain.beta.kubernetes.io/region: <your_region>   # Region of the node where the application is to be deployed
          failure-domain.beta.kubernetes.io/zone: <your_zone>       # AZ of the node where the application is to be deployed
      spec:
        accessModes:
          - ReadWriteOnce               # The value must be ReadWriteOnce for EVS disks.
        resources:
          requests:
            storage: 10Gi             # EVS disk capacity, ranging from 1 to 32768
        storageClassName: csi-disk    # StorageClass is EVS
---
apiVersion: v1
kind: Service
metadata:
  name: statefulset-evs   # Headless Service name
  namespace: default
  labels:
    app: statefulset-evs
spec:
  selector:
    app: statefulset-evs
  clusterIP: None
  ports:
    - name: statefulset-evs
      targetPort: 80
      nodePort: 0
      port: 80
      protocol: TCP
  type: ClusterIP

**Table 2** Key parameters
Parameter	Mandatory	Description
failure-domain.beta.kubernetes.io/region	Yes	Region where the cluster is located. For details about the value of region, see Regions and Endpoints.
failure-domain.beta.kubernetes.io/zone	Yes	AZ where the EVS volume is created. It must be the same as the AZ planned for the workload. For details about the value of zone, see Regions and Endpoints.
everest.io/disk-volume-type	Yes	EVS disk type. All letters are in uppercase. SATA: common I/O SAS: high I/O SSD: ultra-high I/O
everest.io/crypt-key-id	No	Mandatory when the EVS disk is encrypted. Enter the encryption key ID selected during EVS disk creation. To obtain an encryption key ID, log in to the Cloud Server Console. In the navigation pane, choose Elastic Volume Service > Disks. Click the name of the target EVS disk to go to its details page. On the Summary tab page, copy the value of KMS Key ID in the Configuration Information area.
everest.io/disk-volume-tags	No	This field is optional. It is supported when the Everest version in the cluster is 2.1.39 or later. You can add resource tags to classify resources. You can create predefined tags on the TMS console. The predefined tags are available to all resources that support tags. You can use predefined tags to improve the tag creation and resource migration efficiency. CCE automatically creates system tags CCE-Cluster-ID={Cluster ID}, CCE-Cluster-Name={Cluster name}, and CCE-Namespace={Namespace name}. These tags cannot be modified.
csi.storage.k8s.io/fstype	No	This field is optional. It is supported by nodes running CentOS 7 or Ubuntu 22.04, and the Everest version in the cluster must be 2.1.53 or later. You can use it to configure a file system type, which can be ext4 or xfs. If it is left blank, the default value ext4 will be used.
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 PVC capacity, in Gi. The value ranges from 1 to 32768.
storageClassName	Yes	The storage class for EVS disks is csi-disk.

Run the following command to create a workload to which the EVS volume is mounted:
```
kubectl apply -f statefulset-evs.yaml
```
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.

Verifying Data Persistence

View the deployed application and EVS volume files.

Run the following command to view the created pod:

kubectl get pod | grep statefulset-evs

Expected output:

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

Run the following command to check whether the EVS volume has been mounted to the /data path:

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