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How to Expand/Resize NFS Volume

OpenEBS dynamic-nfs-provisioner doesn't support natively expanding NFS volume but we can accomplish the same operation by following a workaround.

For expanding NFS volume, you must ensure the following items(prerequisites) are taken care of:

  • The BackendStorageClass must support volume expansion, which can configure by editing the StorageClass definition to have allowVolumeExpansion: true

    kubectl patch sc openebs-lvmpv -p '{"allowVolumeExpansion": true}'

    storageclass.storage.k8s.io/openebs-lvmpv patched

  • NFS StorageClass must support volume expansion, which can configure by editing the NFS StorageClass defination to have allowVolumeExpansion: true

    kubectl patch sc openebs-rwx -p '{"allowVolumeExpansion": true}'

    storageclass.storage.k8s.io/openebs-rwx patched

Steps to perform NFS Volume Expansion

  • After meeting the prerequisites, Resize NFS volume by editing backend PVC spec.resources.requests.storage to reflect the newly desired size, which must be greater than the original size. 
    kubectl patch pvc <backend-pvc-name> -n <openebs-namespace> -p '{"spec": {"resources": {"requests": {"storage": "10Gi"}}}}'
    Note: OpenEBS dynamic-nfs-provisioner will create backend PVC to provide shared volume and backend PVC has following naming convention nfs-<application-pv-name>. Below command will help to get backend PVC name 
    kubectl get pvc -n <openebs-namespace> -l nfs.openebs.io/nfs-pvc-name=<nfs_pvc_name> -o jsonpath='{.items[0].metadata.name}'
  • Wait till success expansion of backend PVC i.e .status.capacity.storage should match with spec.resources.requests.storage 
    kubectl get pvc <backend-pvc-name> -n <openebs-namespace>
  • Update the NFS PV capacity manually(Since resize is not supported natively by dynamic-nfs provisioner this step will be a workaround) 
    kubectl patch pv <nfs-pv-name> -p '{"spec": {"capacity": {"storage": "2Gi"}}}'
  • Update the NFS PVC capacity 
    kubectl patch pvc <nfs-pvc-name> -n <nfs-pvc-namespace> -p '{"spec": {"resources": {"requests": {"storage": "10Gi"}}}}'

Example

Example to show how to expanding NFS volumes for an already existing StorageClass(backend & NFS StorageClass), you can edit the StorageClass to include the allowVolumeExpansion: true if it is not marked for allowVolumeExpansion.

  • Below YAML shows detailed information about backend StorageClass

    apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  creationTimestamp: "2021-09-09T08:21:34Z"
  name: openebs-lvmpv
parameters:
  storage: lvm
  vgpattern: ^lvm$
provisioner: local.csi.openebs.io
reclaimPolicy: Delete
volumeBindingMode: Immediate
allowVolumeExpansion: true

  • Below YAML shows detailed information about NFS StorageClass

    apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  annotations:
    cas.openebs.io/config: |
      - name: NFSServerType
        value: "kernel"
      - name: BackendStorageClass
        value: "openebs-lvmpv"
    openebs.io/cas-type: nfsrwx
  creationTimestamp: "2021-09-09T08:23:39Z"
provisioner: openebs.io/nfsrwx
reclaimPolicy: Delete
volumeBindingMode: Immediate
allowVolumeExpansion: true

  • Below are the details of Wordpress application consuming RWX volume

    kubectl get pvc -n wordpress

NAME                           STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS    AGE
wordpress-persistent-storage   Bound    pvc-5a8bb1f2-c183-44a7-aa70-12f3138e2a72   1Gi        RWX            openebs-rwx     75m

kubectl get po -n wordpress

NAME                               READY   STATUS    RESTARTS   AGE
wordpress-6db6fb5444-5vj52         1/1     Running   0          76m

kubectl get pv

NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                                                  STORAGECLASS    REASON   AGE
pvc-5a8bb1f2-c183-44a7-aa70-12f3138e2a72   1Gi        RWX            Delete           Bound    wordpress/wordpress-persistent-storage                 openebs-rwx              77m

  • Backend PVC details for above RWX volume

    kubectl get pvc -n openebs

NAME                                           STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS    AGE
nfs-pvc-5a8bb1f2-c183-44a7-aa70-12f3138e2a72   Bound    pvc-2134156f-681e-456b-b6cb-802f754a420f   1Gi        RWO            openebs-lvmpv   85m

  • To Resize the backend PVC, edit the PVC capacity spec.resources.requests.storage to 3Gi. It may take few seconds to update the actual size in PVC resource, wait for the updated capacity to reflect in PVC status(pvc.status.capacity.storage). We can look at events of PVC to know information about resize:

    kubectl patch pvc nfs-pvc-5a8bb1f2-c183-44a7-aa70-12f3138e2a72 -n openebs -p '{"spec": {"resources": {"requests": {"storage": "3Gi"}}}}'

persistentvolumeclaim/nfs-pvc-5a8bb1f2-c183-44a7-aa70-12f3138e2a72 patched
    kubectl describe pvc -n openebs nfs-pvc-5a8bb1f2-c183-44a7-aa70-12f3138e2a72
...
...
Events:
Type     Reason                      Age                From                                   Message
----     ------                      ----               ----                                   -------
Normal   Resizing                    72s (x2 over 67m)  external-resizer local.csi.openebs.io  External resizer is resizing volume pvc-2134156f-681e-456b-b6cb-802f754a420f
Warning  ExternalExpanding           72s (x2 over 67m)  volume_expand                          Ignoring the PVC: didn't find a plugin capable of expanding the volume; waiting for an external controller to process this PVC.
Normal   FileSystemResizeRequired    72s (x2 over 67m)  external-resizer local.csi.openebs.io  Require file system resize of volume on node
Normal   FileSystemResizeSuccessful  6s (x2 over 66m)   kubelet                                MountVolume.NodeExpandVolume succeeded for volume "pvc-2134156f-681e-456b-b6cb-802f754a420f"

  • Update the NFS PV capacity by running following command

    kubectl patch pv pvc-5a8bb1f2-c183-44a7-aa70-12f3138e2a72 -p '{"spec": {"capacity": {"storage": "3Gi"}}}'

  • Now, exec into the wordpress application pod(RWX volume consumer) and check the mount point Available space

    root@wordpress-6db6fb5444-5vj52:/var/www/html# df -h
Filesystem      Size  Used Avail Use% Mounted on
overlay         916G   71G  798G   9% /
tmpfs            64M     0   64M   0% /dev
tmpfs           7.8G     0  7.8G   0% /sys/fs/cgroup
/dev/sda2       916G   71G  798G   9% /etc/hosts
shm              64M     0   64M   0% /dev/shm
----------------------------------------------------------------------
10.0.0.180:/    3.0G   29M  2.9G   1% /var/www/html                   |
----------------------------------------------------------------------
tmpfs            14G   12K   14G   1% /run/secrets/kubernetes.io/serviceaccount

    Above output shows NFS volume has successfully expanded.



Gotcha: NFS PVC will still report old capacity, once dynamic-nfs-provisioner shifts towards CSI it can support dynamically expanding RWX volume.



Tip

  • Download and run script by passing NFS PVC name & namespace as input arguments to test and it will display backend PVC & PV details for given NFS PVC 
    ./get-nfs-volume-details.sh wordpress-persistent-storage wordpress

----------------------------------------------------------------
Backend PVC Name: nfs-pvc-5a8bb1f2-c183-44a7-aa70-12f3138e2a72
Backend PVC Namespace: openebs
Backend PV Name: pvc-2134156f-681e-456b-b6cb-802f754a420f
NFS PV Name: pvc-5a8bb1f2-c183-44a7-aa70-12f3138e2a72
NFS PVC Namespace/Name: wordpress/wordpress-persistent-storage
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