Kubernetes Storage – Part 1 – NFS complete tutorial

In this series of articles, I will discuss available Kubernetes storage solutions with the complete manual for deploying them to/for Kubernetes. This series of tutorials is helpful for everyone who knows the Kubernetes storage architecture and concepts and wants to deploy storage for Stateful applications in Kubernetes.

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Resource Requirements:

• A running Kubernetes cluster. 1.18+ is suggested.
• A running node with some available storage.

I will run the steps on Ubuntu-based systems. I suggest you do so.

For this demonstration, I use two nodes with the following configuration:

A running node used as the NFS server:

OS: Ubuntu 20.04
FQDN: node004.b9tcluster.local
IP Address: 192.168.12.7

A single-node Kubernetes cluster:

OS: Ubuntu 20.04
Kubernetes: 1.21.5 (k3s distribution)
FQDN: node005.b9tcluster.local
IP Address: 192.168.12.8

1- Deploy and configure NFS server:

Run the following commands on the node you considered for the NFS server. You can deploy a clustered NFS server with high availability support.

apt update && apt -y upgrade

apt install -y nfs-server

mkdir /data

cat <<EOF >> /etc/exports
/data 192.168.12.8(rw,no_subtree_check,no_root_squash)
EOF

systemctl enable --now nfs-server

exportfs -ar

These commands install NFS server and export /data , which is accessible by the Kubernetes cluster. In the case of a multi-node Kubernetes cluster, you should allow all Kubernetes worker nodes.

2- Prepare Kubernetes worker nodes:

Now, to connect to the NFS server, the Kubernetes nodes need the NFS client package. You should run the following command only on the Kubernetes worker nodes – and control-plane nodes if they act as workers too.

apt install -y nfs-common

Important tip! Each storage solution may need client packages to connect to the storage server. You should install them in all Kubernetes worker nodes.

For NFS, the nfs-common package is required.

3- Using NFS in Kubernetes:

Method 1 — Connecting to NFS directly with Pod manifest:

To connect to the NFS storage directly using the Pod manifest, use the NFSVolumeSource in the PodSpec. Here is an example:

apiVersion: v1
kind: Pod
metadata:
  name: test
  labels:
    app.kubernetes.io/name: alpine
    app.kubernetes.io/part-of: kubernetes-complete-reference
    app.kubernetes.io/created-by: ssbostan
spec:
  containers:
    - name: alpine
      image: alpine:latest
      command:
        - touch
        - /data/test
      volumeMounts:
        - name: nfs-volume
          mountPath: /data
  volumes:
    - name: nfs-volume
      nfs:
        server: node004.b9tcluster.local
        path: /data
        readOnly: no

Method 2 — Connecting using the PersistentVolume resource:

Use the following manifest to create the PersistentVolume object for the NFS volume. You should note that the storage size does not take any effect.

apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs-volume
  labels:
    storage.k8s.io/name: nfs
    storage.k8s.io/part-of: kubernetes-complete-reference
    storage.k8s.io/created-by: ssbostan
spec:
  accessModes:
    - ReadWriteOnce
    - ReadOnlyMany
    - ReadWriteMany
  capacity:
    storage: 10Gi
  storageClassName: ""
  persistentVolumeReclaimPolicy: Recycle
  volumeMode: Filesystem
  nfs:
    server: node004.b9tcluster.local
    path: /data
    readOnly: no

Method 3 — Dynamic provisioning using StorageClass:

You must install the NFS provisioner to provision PersistentVolume dynamically using StorageClasses. I use the nfs-subdir-external-provisioner to achieve this. The following commands install everything we need using the Helm package manager.

helm repo add nfs-subdir-external-provisioner https://kubernetes-sigs.github.io/nfs-subdir-external-provisioner

helm install nfs-subdir-external-provisioner nfs-subdir-external-provisioner/nfs-subdir-external-provisioner \
  --create-namespace \
  --namespace nfs-provisioner \
  --set nfs.server=node004.b9tcluster.local \
  --set nfs.path=/data

To create the PersistentVolumeClaim, use the following manifest:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: nfs-test
  labels:
    storage.k8s.io/name: nfs
    storage.k8s.io/part-of: kubernetes-complete-reference
    storage.k8s.io/created-by: ssbostan
spec:
  accessModes:
    - ReadWriteMany
  storageClassName: nfs-client
  resources:
    requests:
      storage: 1Gi

4- Kubernetes and NFS storage specification:

NFS has the following specifications in the Kubernetes world. It would help to consider them before using the NFS storage in production.

• ReadWriteOnce, ReadOnlyMany, and ReadWriteMany access modes.
• The storage size does not take any effect!
• In the case of dynamic provisioning, volumes are separated into different directories but without access controls or proper isolation.

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