Use a Deployment to create ephemeral volumes

Ephemeral volumes can be used to store temporary data such as cache data. When you create a Deployment, you can use the persistent volume claim (PVC) template VolumeClaimTemplate to create an ephemeral volume for each pod. The PVCs and persistent volumes (PVs) created by using this PVC template can be automatically deleted together with the pods that use them. This topic describes how to use a Deployment to create ephemeral volumes and how to verify that the ephemeral volumes can be deleted together with the pods.

Prerequisites

A Container Service for Kubernetes (ACK) cluster that runs Kubernetes 1.22 or later is created. For more information, see Create an ACK managed cluster.

Note

You cannot use Deployments to create ephemeral volumes for ACK Serverless clusters.

Use scenarios

Applications use ephemeral volumes to store temporary data that does not need to be persisted.
Applications usually generate large amounts of log data. You can use ephemeral, exclusive volumes to store log data.

When you create a Deployment, you can use VolumeClaimTemplate to automatically create PVCs and PVCs. VolumeClaimTemplate is a PVC template. The number of PVCs that the system creates with this template is equal to the number of replicated pods specified in the Deployment. The PVCs use the same configuration but different names.

Use the following code block to create a Deployment that deploys two pods.

In addition to Deployments, you can also create ephemeral volumes by using StatefulSets and pod YAML files.

Click to view the YAML content of the Deployment

allowVolumeExpansion: true
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  creationTimestamp: "2023-07-19T06:54:25Z"
  name: alicloud-disk-topology-alltype
  resourceVersion: "773847"
  uid: 5a9f8e3b-d22e-483d-a3bf-90ff8d466492
parameters:
  type: cloud_essd,cloud_ssd,cloud_efficiency
provisioner: diskplugin.csi.alibabacloud.com
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer
---
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: busybox-container
          image: busybox
          resources:
            requests:
              cpu: 500m
              memory: 2Gi
              ephemeral-storage: 2Gi
          volumeMounts:
          - mountPath: "/scratch"
            name: scratch-volume
          command: [ "sleep", "1000000" ]
      volumes:
        - name: scratch-volume
          ephemeral:
            volumeClaimTemplate:
              metadata:
                labels:
                  type: scratch-volume
              spec:
                accessModes: [ "ReadWriteOnce" ]
                storageClassName: alicloud-disk-topology-alltype
                resources:
                  requests:
                    storage: 30Gi

Parameter	Description
replicas	In this example, two replicated pods are created.
volumeMounts.mountPath	The container path to which the disk volume is mounted.
accessModes	The access mode.
ephemeral	Set the volume type to ephemeral.
storageClassName	In this example, the parameter is set to alicloud-disk-topology-alltype. The system attempts to create volumes based on the following disk types in sequence: cloud_essd, cloud_ssd, and cloud_efficiency.

Run the following command to deploy the Deployment:
```
kubectl create -f ephemeral-example.yaml
```

Run the following command to query pods:

kubectl get pod

Expected output:

NAME                                 READY   STATUS    RESTARTS   AGE
ephemeral-example-65d6c5fb87-5jbjf   1/1     Running   0          4m55s
ephemeral-example-65d6c5fb87-jgt8x   1/1     Running   0          4m55s

Run the following command to query PVCs:

kubectl get pvc

Expected output:

NAME                                                STATUS   VOLUME                   CAPACITY   ACCESS MODES   STORAGECLASS                     AGE
ephemeral-example-65d6c5fb87-5jbjf-scratch-volume   Bound    d-2ze7cjui6henh7z61393   30Gi       RWO            alicloud-disk-topology-alltype   5m42s
ephemeral-example-65d6c5fb87-jgt8x-scratch-volume   Bound    d-2zehi4gnz4btacaf8lh2   30Gi       RWO            alicloud-disk-topology-alltype   5m42s

Verify that the PVCs and PVs are deleted together with the pods

Run the following command to scale the number of pods to 1:

kubectl scale deploy ephemeral-example --replicas=1
deployment.apps/ephemeral-example scaled

Run the following command to query the number of pods:

kubectl get pod

Expected output:

NAME                                 READY   STATUS        RESTARTS   AGE
ephemeral-example-65d6c5fb87-5jbjf   1/1     Terminating   0          7m13s
ephemeral-example-65d6c5fb87-jgt8x   1/1     Running       0          7m13s

Run the following command to query the number of PVCs:

kubectl get pvc

Expected output:

NAME                                                STATUS   VOLUME                   CAPACITY   ACCESS MODES   STORAGECLASS                     AGE
ephemeral-example-65d6c5fb87-jgt8x-scratch-volume   Bound    d-2zehi4gnz4btacaf8lh2   30Gi       RWO            alicloud-disk-topology-alltype   8m1s

The output indicates that the PVC is deleted together with the pod.

References

For more information about how to monitor the usage of ephemeral volumes, see Use storage-operator to monitor the storage resources of an ACK cluster.
For more information about how to use disks to persist data, see Disk volumes.