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 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 CCE Container Storage (Everest) add-on in the cluster.
• Before creating a cluster using commands, ensure kubectl is used to access the cluster. For details, see Connecting to a Cluster Using kubectl.

(Console) Dynamically Mounting an EVS Disk

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 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.
   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. NOTE: If the Everest version is 2.4.4 or later, general-purpose SSD V2 and extreme SSD V2 are supported. General-purpose SSD V2 disks allow you to specify the disk IOPS and throughput. For details, see the .
   Access Mode	EVS disks support only ReadWriteOnce, indicating that a storage volume can be mounted to one node in read/write mode. For details, see Volume Access Modes.
   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, 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. 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 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 Using 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.
   
   
           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    # The storage class 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
   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.

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 view 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 view 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

   If the static file still exists, the data in the EVS volume can be stored persistently.

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