ref: Respect idempotency in CreateVolume(...)

[lgarber-akamai]

General:

This change updates the LinodeControllerServer.CreateVolume(...) logic to respect the idempotency requirements described in the CSI spec. This change should hopefully make volume creation more reliable, especially for long-running and error-prone operations like large volume cloning.

Testing:

E2E Testing

Not currently implemented, see #140.

Manual Testing

NOTE: These steps would previously fail because a pre-existing volume would not be respected by CreateVolume(...) after a timeout error.

1. Build the OCI image and push it to an image registry:

   export REGISTRY_NAME=index.docker.io/mydockerhubuser
   export IMAGE_VERSION=dev

2. Provision a Kubernetes cluster on Linode. (e.g. RKE2)

3. Navigate to helm-chart/csi-driver.

4. Update values.yaml to point to the image pushed in step 1.

5. Deploy the Helm chart to your Kubernetes cluster:

   export KUBECONFIG=mykubeconfig.yaml
   helm install linode-bs-csi .

6. Apply a linode-block-storage PVC and a job to populate it with random data:

   kubectl apply -f - <<EOF
   apiVersion: v1
   kind: PersistentVolumeClaim
   metadata:
   name: pvc-1
   spec:
   accessModes:
   - ReadWriteOnce
   resources:
   requests:
     storage: 100Gi
   storageClassName: linode-block-storage
   ---
   apiVersion: batch/v1
   kind: Job
   metadata:
   name: pvc-populator
   spec:
   template:
   spec:
     containers:
       - name: populate
         image: alpine:latest
         command: ["dd", "if=/dev/urandom", "of=/mnt/pvc/foo", "bs=1M", "count=75000"]
         volumeMounts:
           - mountPath: /mnt/pvc
             name: data
     volumes:
       - name: data
         persistentVolumeClaim:
           claimName: pvc-1
     restartPolicy: Never
   EOF

7. Wait for the job to complete.

   kubectl wait --for=condition=complete job/pvc-populator 

8. Create a new PVC cloned from the first PVC (this should take several minutes to finish)

   kubectl apply -f - <<EOF
   apiVersion: v1
   kind: PersistentVolumeClaim
   metadata:
   name: pvc-2
   spec:
   accessModes:
   - ReadWriteOnce
   resources:
   requests:
     storage: 100Gi
   storageClassName: linode-block-storage
   dataSource:
   kind: PersistentVolumeClaim
   name: pvc-1
   EOF

9. Once the corresponding Linode volume has finished provisioning, observe that the PVC is bound in Kubernetes.

10. Ensure that only one Linode volume clone event has occurred.

11. (Optional) Check the CSI controller logs to see the volume creation fail repeatedly until it eventually reconciles.