Container Service for Kubernetes:Use disks as ephemeral volumes

Scenarios

This method is suitable for scenarios that require ephemeral storage, such as:

• Your application needs ephemeral storage to save intermediate data but does not require the data to be persistent.

• Your application outputs logs with high throughput. Using temporary, non-shared storage helps ensure storage performance.

Prerequisites

An ACK cluster that runs version 1.22 or later has been created.

Create a deployment and mount an ephemeral volume

When you create a deployment, you can use a VolumeClaimTemplate to automatically create a PVC and a PV. A VolumeClaimTemplate is a template that defines PVCs. The system creates a number of PVCs based on the number of replicas specified in the deployment configuration. These PVCs share the same configuration, except for their names.

1. Modify the following YAML content based on the parameter descriptions in the table. Save the content as ephemeral-example.yaml.

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: ephemeral-example
   spec:
     replicas: 2
     selector:
       matchLabels:
         pod: example-pod
     strategy:
       type: Recreate      
     template:
       metadata:
         labels:
           pod: example-pod
       spec:
         containers:
           - name: nginx
             image: anolis-registry.cn-zhangjiakou.cr.aliyuncs.com/openanolis/nginx:1.14.1-8.6
             resources:
               requests:
                 cpu: 500m
                 memory: 2Gi
                 ephemeral-storage: 2Gi
             volumeMounts:
             - mountPath: "/scratch"
               name: scratch-volume
         volumes:
           - name: scratch-volume
             ephemeral:      # Declare the current storage as ephemeral storage
               volumeClaimTemplate:
                 spec:
                   accessModes: [ "ReadWriteOncePod" ]
                   storageClassName: alicloud-disk-topology-alltype
                   resources:
                     requests:
                       storage: 30Gi

   The following table describes the parameters in volumeClaimTemplate.

   Parameter	Description
   accessModes	The access mode of the persistent volume. You can set this parameter to ReadWriteOncePod or ReadWriteOnce. If your cluster is version 1.29 or later, use ReadWriteOncePod. This ensures that a disk is used by only one pod.
   storageClassName	The name of the StorageClass to use. This example uses alicloud-disk-topology-alltype, which is a default StorageClass provided by ACK. This StorageClass defines the configuration for disk volumes. It attempts to create disks in the following order: enterprise SSD (ESSD), standard SSD, and ultra disk. Note Disks are billed on a pay-as-you-go basis. For more information, see Elastic Block Storage billing and Elastic Block Storage pricing.
   storage	The capacity of the ephemeral volume. Note The StorageClass used in the example (alicloud-disk-topology-alltype) creates a PL1 ESSD by default. The minimum capacity is 20 GiB.

2. Use the ephemeral-example.yaml file to create the deployment.

   kubectl create -f ephemeral-example.yaml

3. Check the deployment status of the pods.

   kubectl get pod -l pod=example-pod

   Expected output:

   NAME                                 READY   STATUS    RESTARTS   AGE
   ephemeral-example-7f795798f9-kbplx   1/1     Running   0          38s
   ephemeral-example-7f795798f9-p98lt   1/1     Running   0          38s

4. Check the PVCs.

   kubectl get pvc

   The following output is expected. The PVCs and PVs that correspond to the pods are automatically created. The disk ID is in the VOLUME field.

   NAME                                                STATUS   VOLUME                   CAPACITY   ACCESS MODES   STORAGECLASS                     VOLUMEATTRIBUTESCLASS   AGE
   ephemeral-example-7f795798f9-kbplx-scratch-volume   Bound    d-uf61678cuo33eunn****   30Gi       RWOP           alicloud-disk-topology-alltype   <unset>                 74s
   ephemeral-example-7f795798f9-p98lt-scratch-volume   Bound    d-uf6dwkdcowyf2fj6****   30Gi       RWOP           alicloud-disk-topology-alltype   <unset>                 74s

Verify that the PV and PVC are deleted when the pod is scaled in

When you create the deployment as described in the previous section, a disk is automatically mounted to each pod as an ephemeral volume. These volumes are automatically deleted when their corresponding pods are deleted. The following example demonstrates how to verify this behavior.

1. Reduce the number of replicas for the deployment.

   The following command reduces the number of replicas in the deployment to 1.

   kubectl scale deploy ephemeral-example --replicas=1

2. Check the pods to confirm that the scale-in is complete.

   kubectl get pod -l pod=example-pod

   Expected output:

   NAME                                 READY   STATUS    RESTARTS   AGE
   ephemeral-example-7f795798f9-kbplx   1/1     Running   0          5m29s

3. Check the PVs and PVCs to confirm that the resources for the deleted pod are also deleted.

   1. Check the PVs.

      kubectl get pv

      The following output is expected. The PV for the deleted pod is also deleted.

      NAME                     CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                                                       STORAGECLASS                     VOLUMEATTRIBUTESCLASS   REASON   AGE
      d-uf61678cuo33eunn****   30Gi       RWOP           Delete           Bound    default/ephemeral-example-7f795798f9-kbplx-scratch-volume   alicloud-disk-topology-alltype   <unset>                          5m52s

   2. Check the PVCs.

      kubectl get pvc

      The following output is expected. The PVC for the deleted pod is also deleted.

      NAME                                                STATUS   VOLUME                   CAPACITY   ACCESS MODES   STORAGECLASS                     VOLUMEATTRIBUTESCLASS   AGE
      ephemeral-example-7f795798f9-kbplx-scratch-volume   Bound    d-uf61678cuo33eunn****   30Gi       RWOP           alicloud-disk-topology-alltype   <unset>                 7m11s

References

• For more information about how to monitor the usage of ephemeral storage, see Ephemeral storage monitoring.

• For more information about using disks for persistent storage, see Disk volumes.