Dynamically Mounting an EVS Disk 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.

When updating a StatefulSet in Kubernetes, it is not allowed to add or delete the volumeClaimTemplates field. This field can only be configured during the creation of the StatefulSet.

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

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 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 default StorageClass for EVS disks is csi-disk.
   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.
   Enterprise Project	The default enterprise project, the enterprise project to which the cluster belongs, or the enterprise project specified by StorageClass is available.

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. This may lead to container errors. 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 will be 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.

   

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 an EVS Volume Through kubectl

1. Use kubectl to access the cluster.
2. 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/enterprise-project-id: <your_project_id>  # (Optional) Enterprise project ID. If an enterprise project is specified, use the same enterprise project when creating a PVC. Otherwise, the PVC cannot be bound to a PV.
   
   
   
           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.
   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.
   everest.io/disk-volume-type	Yes	EVS disk type. All letters are in uppercase. SAS: high I/O SSD: ultra-high I/O
   everest.io/enterprise-project-id	No	Optional. Enterprise project ID of the EVS disk. If an enterprise project is specified, use the same enterprise project when creating a PVC. Otherwise, the PVC cannot be bound to a PV. To obtain an enterprise project 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, click the enterprise project in Management Information to access the enterprise project console. Copy the corresponding ID to obtain the ID of the enterprise project to which the EVS disk belongs.
   storage	Yes	Requested PVC capacity, in Gi. The value ranges from 1 to 32768.
   storageClassName	Yes	The StorageClass for EVS disks is csi-disk.

3. 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

1. View the deployed application and EVS volume files.
   1. 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

   2. 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

      Expected output:

      /dev/sdd              10255636     36888  10202364   0% /data

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

      kubectl exec statefulset-evs-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-evs-0 --  touch /data/static

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

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

   Expected output:

   lost+found
   static

4. Run the following command to delete the pod named web-evs-auto-0:

   kubectl delete pod statefulset-evs-0

   Expected output:

   pod "statefulset-evs-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-evs-0 -- ls /data

   Expected output:

   lost+found
   static

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

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