I tried to connect nfs, which is provided by nas, to k3s cluster, and now I'm going to note of that journey.

0. The goal
1. Set up nfs server in iptime nas
2. Concept of storage class, persistent volume, and persistent volume claim
3. Build nfs storage class: installing driver, defining manifest file

0. The goal

I've been studying kubernetes and deployed some oss on my own cluster without knowing concept of volumes in kubernetes.
and I watched youtube video explaining what it is, and decided to use storage class to connect persistent volumes to apps on my cluster.

1. Set up nfs server in iptime nas

ref

/opt/sbin/portmap
/opt/sbin/unfsd -e /opt/etc/exports 

2. Concept of volumes in kubernetes

flowchart TD
    subgraph cluster
        subgraph namespace
            APP[application] --> PVC[persistent volume claim]
        end

        PVC --> NFS_SC[nfs storage class]
        PVC --> CL_SC[cloud storage class]
    end

    NFS_SC --> NFS[NFS server]
    CL_SC --> AZURE[e.g. Azure files]

pod -> persistent volume claim -> persistent volume

• persistent volume: cluster-wide concept
• persistent volume claim: concept in namespace

If we use pure persistent volume, we need to set one persistent volume per one persistent volume claim. So it needs to be 1:1 mapping.

However, Storage Class does mapping automatically.

3. NFS Storage class

3.1. NFS driver

Need to install kubernetes Container Storage Interface (CSI) first, github.

1. Add helm repo

helm repo add csi-driver-nfs https://raw.githubusercontent.com/kubernetes-csi/csi-driver-nfs/master/charts

2. Install with specific version

nfs storage class checkout parameters for the provisioner here

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: example-nfs
provisioner: example.com/external-nfs
parameters:
  server: nfs-server.example.com
  path: /share
  readOnly: "false"

3. ERRORRRRRRR I got following at the first time:

Warning  ProvisioningFailed    1s                 nfs.csi.k8s.io_agent-00_b97d6068-d50e-4296-b946-78e305338f70  failed to provision volume with StorageClass "iptime-nas-nfs": rpc error: code = Internal desc = failed to mount nfs server: rpc error: code = Internal desc = mount failed: exit status 32

and found stackoverflow post. Need to install nfs-common to every k3s node.

4. Change default storage class

Usually if you don't specifiy storage class to be used in a persistent volume claim, it uses default storage class. In my case, it was like follows:

rst@Wonbinui-MacBookPro ~ % kubectl get storageclass
NAME                   PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
iptime-nas-nfs         nfs.csi.k8s.io          Delete          Immediate              false                  3h45m
local-path (default)   rancher.io/local-path   Delete          WaitForFirstConsumer   false  

I changed the default storage class because its hard find all helm chart's pvc.

The first thing we need to do is marking default storage class as non-default. In my case, It would be like

kubectl patch storageclass local-path -p '{"metadata": {"annotations":{"storageclass.kubernetes.io/is-default-class":"false"}}}'

The second thing is marking the storage class you want as default storage class

kubectl patch storageclass iptime-nas-nfs -p '{"metadata": {"annotations":{"storageclass.kubernetes.io/is-default-class":"true"}}}'

Now you can see like

rst@Wonbinui-MacBookPro ~ % kubectl get storageclass  
NAME                       PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
iptime-nas-nfs (default)   nfs.csi.k8s.io          Delete          Immediate              false                  3h49m
local-path                 rancher.io/local-path   Delete          WaitForFirstConsumer   false                  13d