pod-single-existing-volume

Use an existing volume

Below you will find the instruction on how to use an existing DigitalOcean Block Storage with your Kubernetes cluster.

Known issues

• Deleting a PVC will delete the volume if the reclaim policy is set to Delete, however the bound PV will be not deleted. This seems to be a bug in K8S.
• Using an existing, attached volume might cause confusion if the POD is scheduled to a different node. It's advised to use only existing detached volumes. If you have an attached volume, please make sure to detach it, so Kubernetes attaches it to the correct droplet. The CSI plugin will return an error if the volume is attached to a wrong droplet.

Example

To use an existing volume, we have to create manually a PersistentVolume (PV) resource. Here is an example PersistenVolume resource for an existing volume:

kind: PersistentVolume
apiVersion: v1
metadata:
  name: volume-nyc1-01
  annotations:
    # fake it by indicating this is provisioned dynamically, so the system
    # works properly
    pv.kubernetes.io/provisioned-by: dobs.csi.digitalocean.com
spec:
  storageClassName: do-block-storage
  # by default, the volume will be not deleted if you delete the PVC, change to
  # "Delete" if you wish the volume to be deleted automatically with the PVC
  persistentVolumeReclaimPolicy: Delete
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce
  csi:
    driver: dobs.csi.digitalocean.com
    fsType: ext4
    volumeHandle: 1952d58a-c714-11e8-bc0c-0a58ac14421e
    volumeAttributes:
      com.digitalocean.csi/noformat: "true"

Couple of things to note,

• volumeHandle is the volume ID you want to reuse. Make sure it matches exactly the volume you're targeting. You can list the ID's of your volumes via doctl: doctl compute volume list
• volumeAttributes has a special, csi-digitalocean specific annotation called com.digitalocean.csi/noformat. If you add this key, the CSI plugin makes sure to not format the volume. If you don't add this, it'll be formatted.
• storage make sure it's set to the same storage size as your existing DigitalOcean Block Storage volume.

Create a file with this content, naming it pv.yaml and deploying it:

kubectl create -f pv.yaml

View information about the PersistentVolume:

$ kubectl get pv volume-nyc1-01

NAME             CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM     STORAGECLASS       REASON    AGE
volume-nyc1-01   5Gi        RWO            Delete           Available             do-block-storage             15s

The status is Available. This means it has not yet been bound to a PersistentVolumeClaim. Now we can proceed to create our PVC:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: csi-pod-pvc
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 5Gi
  storageClassName: do-block-storage

This is the same (just like our other examples). When you create PVC, Kubernetes will try to match it to an existing PV. Because the storageClassName and the storage size matches our PV descriptions, kubernetes will bind this PVC to our manually create PV. CSI will not create a new volume because of the existing PV.

Create the PersistentVolumeClaim:

kubectl create -f pvc.yaml

Now look at the PersistentVolumeClaim (PVC):

kubectl get pvc task-pv-claim
NAME          STATUS    VOLUME           CAPACITY   ACCESS MODES   STORAGECLASS       AGE
csi-pod-pvc   Bound     volume-nyc1-01   5Gi        RWO            do-block-storage   5s

As you see, the output shows that the PVC is bound to our PersistentVolume, volume-nyc1-01.

Finally, define your pod that refers to this PVC:

kind: Pod
apiVersion: v1
metadata:
  name: my-csi-app
spec:
  containers:
    - name: my-frontend
      image: busybox
      volumeMounts:
      - mountPath: "/data"
        name: my-do-volume
      command: [ "sleep", "1000000" ]
  volumes:
    - name: my-do-volume
      persistentVolumeClaim:
        claimName: csi-pod-pvc 

Check if the pod is running successfully:

$ kubectl describe pods/my-csi-app

Write inside the app container:

$ kubectl exec -ti my-csi-app /bin/sh
/ # touch /data/hello-world
/ # exit
$ kubectl exec -ti my-csi-app /bin/sh
/ # ls /data
hello-world