Create clones of persistent volumes

Autopilot Standard

This document shows you how to use Kubernetes volume cloning to clone persistent volumes in your Google Kubernetes Engine (GKE) clusters.

Overview

A clone is a new independent volume that is a duplicate of an existing Kubernetes volume. A clone is similar to a volume snapshot in that it's a copy of a volume at a specific point in time. However, rather than creating a snapshot object from the source volume, volume cloning provisions the clone with all the data from the source volume.

Requirements

To use volume cloning on GKE, you must meet the following requirements:

The source PersistentVolumeClaim must be in the same namespace as the destination PersistentVolumeClaim.
Use a CSI driver that supports volume cloning. The in-tree persistent disk driver does not support volume cloning.
- The Compute Engine persistent disk CSI Driver version 1.4.0 and later supports volume cloning, and is installed by default on new Linux clusters running GKE version 1.22 or later. You can also enable the Compute Engine persistent disk CSI Driver on an existing cluster.

To verify the Compute Engine persistent disk CSI Driver version, run the following command in the gcloud CLI:

kubectl describe daemonsets pdcsi-node --namespace=kube-system | grep "gke.gcr.io/gcp-compute-persistent-disk-csi-driver"

If the output shows a version earlier than 1.4.0, manually upgrade your control plane to get the latest version.

Limitations

Both volumes must use the same volume mode. By default, GKE sets the VolumeMode to ext4.
All restrictions for creating a disk clone from an existing disk on Compute Engine also apply to GKE.
You can create a regional disk clone from a zonal disk, but you should be aware of the restrictions of this approach.
Cloning must be done in a compatible zone. Use allowedTopologies to restrict the topology of provisioned volumes to specific zones. Alternatively, nodeSelectors or Affinity and anti-affinity can be used to constrain a Pod so that it is restricted to run on particular node that runs in a compatible zone.
- For zonal to zonal cloning, the clone zone must match the source disk zone.
- For zonal to regional cloning, one of the replica zones of the clone must match the zone of the source disk.

Using volume cloning

To provision a volume clone, you add a reference to an existing PersistentVolumeClaim in the same namespace to the dataSource field of a new PersistentVolumeClaim. The following exercise shows you how to provision a source volume with data, create a volume clone, and consume the clone.

Create a source volume

To create a source volume, follow the instructions in Using the Compute Engine persistent disk CSI Driver for Linux clusters to create a StorageClass, a PersistentVolumeClaim, and a Pod to consume the new volume. You'll use the PersistentVolumeClaim that you create as the source for the volume clone.

Add a test file to the source volume

Add a test file to the source volume. You can look for this test file in the volume clone to verify that cloning was successful.

Create a test file in a Pod:
```
kubectl exec POD_NAME \
    -- sh -c 'echo "Hello World!" > /var/lib/www/html/hello.txt'
```
Replace POD_NAME with the name of a Pod that consumes the source volume. For example, if you followed the instructions in Using the Compute Engine persistent disk CSI Driver for Linux clusters, replace POD_NAME with web-server.

Verify that the file exists:

kubectl exec POD_NAME \
    -- sh -c 'cat /var/lib/www/html/hello.txt'

The output is similar to the following:

Hello World!

Clone the source volume

Save the following manifest as podpvc-clone.yaml:
```
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: podpvc-clone
spec:
  dataSource:
    name: PVC_NAME
    kind: PersistentVolumeClaim
  accessModes:
  - ReadWriteOnce
  storageClassName: STORAGE_CLASS_NAME
  resources:
    requests:
      storage: STORAGE
```
Replace the following:
- PVC_NAME: the name of the source PersistentVolumeClaim that you created in Create a source volume.
- STORAGE_CLASS_NAME: the name of the StorageClass to use, which must be the same as the StorageClass of the source PersistentVolumeClaim.
- STORAGE: the amount of storage to request, which must be at least the size of the source PersistentVolumeClaim.
Apply the manifest:
```
kubectl apply -f podpvc-clone.yaml
```

Create a Pod that consumes the cloned volume

The following example creates a Pod that consumes the volume clone that you created.

Save the following manifest as web-server-clone.yaml:

apiVersion: v1
kind: Pod
metadata:
  name: web-server-clone
spec:
  containers:
   - name: web-server-clone
     image: nginx
     volumeMounts:
       - mountPath: /var/lib/www/html
         name: mypvc
  volumes:
   - name: mypvc
     persistentVolumeClaim:
       claimName: podpvc-clone
       readOnly: false

Apply the manifest:
```
kubectl apply -f web-server-clone.yaml
```

Verify that the test file exists:

kubectl exec web-server-clone \
    -- sh -c 'cat /var/lib/www/html/hello.txt'