Use NFS for Persistent Volumes on MicroK8s

evilnick
Thu, 10 Feb 2022 12:21:33 +0000
microk8s

In this how-to we will explain how to provision NFS mounts as Kubernetes Persistent Volumes on MicroK8s. If you run into difficulties, please see the troubleshooting section at the end!

Setup an NFS server

Caution: This section will show you how to configure a simple NFS server on Ubuntu for the purpose of this tutorial. This is not a production-grade NFS setup.

If you don’t have a suitable NFS server already, you can simply create one on a local machine with the following commands on Ubuntu:

sudo apt-get install nfs-kernel-server

Create a directory to be used for NFS:

sudo mkdir -p /srv/nfs
sudo chown nobody:nogroup /srv/nfs
sudo chmod 0777 /srv/nfs

Edit the /etc/exports file. Make sure that the IP addresses of all your MicroK8s nodes are able to mount this share. For example, to allow all IP addresses in the 10.0.0.0/24 subnet:

sudo mv /etc/exports /etc/exports.bak
echo '/srv/nfs 10.0.0.0/24(rw,sync,no_subtree_check)' | sudo tee /etc/exports

Finally, restart the NFS server:

sudo systemctl restart nfs-kernel-server

For other OSes, follow specific documentation.

Install the CSI driver for NFS

We will use the upstream NFS CSI driver. First, we will deploy the NFS provisioner using the official Helm chart.

Enable the Helm3 addon (if not already enabled) and add the repository for the NFS CSI driver:

microk8s enable helm3
microk8s helm3 repo add csi-driver-nfs https://raw.githubusercontent.com/kubernetes-csi/csi-driver-nfs/master/charts
microk8s helm3 repo update

Then, install the Helm chart under the kube-system namespace with:

microk8s helm3 install csi-driver-nfs csi-driver-nfs/csi-driver-nfs \
    --namespace kube-system \
    --set kubeletDir=/var/snap/microk8s/common/var/lib/kubelet

After deploying the Helm chart, wait for the CSI controller and node pods to come up using the following kubectl command …

microk8s kubectl wait pod --selector app.kubernetes.io/name=csi-driver-nfs --for condition=ready --namespace kube-system

… which, once successful, will produce output similar to:

pod/csi-nfs-controller-67bd588cc6-7vvn7 condition met
pod/csi-nfs-node-qw8rg condition met

At this point, you should also be able to list the available CSI drivers in your Kubernetes cluster …

microk8s kubectl get csidrivers

… and see nfs.csi.k8s.io in the list:

NAME             ATTACHREQUIRED   PODINFOONMOUNT   STORAGECAPACITY   TOKENREQUESTS   REQUIRESREPUBLISH   MODES        AGE
nfs.csi.k8s.io   false            false            false             <unset>         false               Persistent   39m

Create a StorageClass for NFS

Next, we will need to create a Kubernetes Storage Class that uses the nfs.csi.k8s.io CSI driver. Assuming you have configured an NFS share /srv/nfs and the address of your NFS server is 10.0.0.42, create the following file:

# sc-nfs.yaml
---
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: nfs-csi
provisioner: nfs.csi.k8s.io
parameters:
  server: 10.0.0.42
  share: /srv/nfs
reclaimPolicy: Delete
volumeBindingMode: Immediate
mountOptions:
  - hard
  - nfsvers=4.1

Note: The last line of the above YAML indicates a specific version of NFS. This should match the version of the NFS server being used - if you are using an existing service please check which version it uses and adjust accordingly.

Then apply it on your MicroK8s cluster with:

microk8s kubectl apply -f - < sc-nfs.yaml

Create a new PVC

The final step is to create a new PersistentVolumeClaim using the nfs-csi storage class. This is as simple as specifying storageClassName: nfs-csi in the PVC definition, for example:

# pvc-nfs.yaml
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-pvc
spec:
  storageClassName: nfs-csi
  accessModes: [ReadWriteOnce]
  resources:
    requests:
      storage: 5Gi

Then create the PVC with:

microk8s kubectl apply -f - < pvc-nfs.yaml

If everything has been configured correctly, you should be able to check the PVC…

microk8s kubectl describe pvc my-pvc

… and see that a volume was provisioned successfully:

Name:          my-pvc
Namespace:     default
StorageClass:  nfs-csi
Status:        Bound
Volume:        pvc-5676d353-4d46-49a2-b7ff-bdd4603d2c06
Labels:        <none>
Annotations:   pv.kubernetes.io/bind-completed: yes
               pv.kubernetes.io/bound-by-controller: yes
               volume.beta.kubernetes.io/storage-provisioner: nfs.csi.k8s.io
               volume.kubernetes.io/storage-provisioner: nfs.csi.k8s.io
Finalizers:    [kubernetes.io/pvc-protection]
Capacity:      5Gi
Access Modes:  RWO
VolumeMode:    Filesystem
Used By:       <none>
Events:
  Type     Reason                 Age                    From                                                           Message
  ----     ------                 ----                   ----                                                           -------
  Normal   ExternalProvisioning   2m59s (x2 over 2m59s)  persistentvolume-controller                                    waiting for a volume to be created, either by external provisioner "nfs.csi.k8s.io" or manually created by system administrator
  Normal   Provisioning           2m58s (x2 over 2m59s)  nfs.csi.k8s.io_andromeda_61e4b876-324d-4f52-a5c3-f26047fbbc97  External provisioner is provisioning volume for claim "default/my-pvc"
  Normal   ProvisioningSucceeded  2m58s                  nfs.csi.k8s.io_andromeda_61e4b876-324d-4f52-a5c3-f26047fbbc97  Successfully provisioned volume pvc-5676d353-4d46-49a2-b7ff-bdd4603d2c06

That’s it! You can now use this PVC to run stateful workloads on your MicroK8s cluster.

Common Issues
The NFS CSI controller and node pods are getting stuck in `Pending` state (click for more details) I created the nfs-csi storage class, but cannot provision volumes (click for more details) Provisioning new volumes fails, but I've done everything else correctly (click for more details)
34 posts - 18 participants