Infrastructure at your Service

Mehdi Bada

NFS Storage Configuration for Kubernetes

For one of our important customers, we are working on a major project to migrate critical applications to containers. From the implementation of the Kubernetes architecture to the deployment of applications and the administration of the platform, we are responsible for an important technological stack with new challenges for our team.

One of the challenges, both important and exciting, is the implementation of Kubernetes clusters on bare metal (VM) and its management. We have deployed a Kubernetes cluster in VMs, based on VMWare.

As you know, one of the challenges of containerization is storage management. Do we manage stateless or stateful applications? For stateful applications, the way the data generated by the application is stored is very important.

Therefore, based on our infrastructure, we have 2 possibilities:

Here is a representative diagram of the 2 solutions:

Configuring NFS storage for Kubernetes

The Kubernetes infrastructure is composed of the following:

  • k8s-master
  • k8s-worker1
  • k8s-worker2

In addition, we have an NFS server to store our cluster data. In the next steps, we are going to expose the NFS share as a cluster object. We will create Kubernetes Persistent Volumes and Persistent Volume Claims for our application.

Persistent Volume Creation

Define the persistent volume at the cluster level as following:

[[email protected] ~]$ vi create-pv.yaml
apiVersion: v1
kind: PersistentVolume
metadata:
name: nfs-demo
labels:
app: nfs
type: data
spec:
accessModes:
- ReadWriteOnce
capacity:
storage: 10Gi
volumeMode: Filesystem
nfs:
path: /home/ec2-user/data
server: ec2-3-88-194-14.compute-1.amazonaws.com
persistentVolumeReclaimPolicy: Retain

Create the persistent volume and see the results:

[[email protected] ~]$ kubectl create -f create-pv.yaml
persistentvolume/nfs-demo created
[[email protected] ~]$ kubectl get pv
NAME       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM   STORAGECLASS   REASON   AGE
nfs-demo   10Gi       RWO            Retain           Available                                   7s

Once it’s created we can create a persistent volume claim. A PVC is dedicated to a specific namespace.
First, create the nfs-demo namespace, then the PVC.

[[email protected] ~]$ kubectl create ns nfs-demo
namespace/nfs-demo created
[[email protected] ~]$ vi create-pvc.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: nfs-demo
  namespace: nfs-demo
  labels:
   app: nfs
spec:
  accessModes:
    - ReadWriteOnce
  resources:
     requests:
       storage: 10Gi
  selector:
    matchLabels:
      app: nfs
      type: data
[[email protected] ~]$ kubectl create -f create-pvc.yaml
persistentvolumeclaim/nfs-demo created

[[email protected] ~]$ kubectl get pvc -n nfs-demo
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
nfs-demo Bound nfs-demo 10Gi RWO 3m21s

We can see now that our persistent volume changes its status from “Available” to “Bound”.

[[email protected] ~]$ kubectl get pv
NAME       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM               STORAGECLASS   REASON   AGE
nfs-demo   10Gi       RWO            Retain           Bound    nfs-demo/nfs-demo                           169m

Finally, let’s deploy now our workload which will consume the volume claim and the persistent volume. Whatever the workload API object you are using (Deployment, StatefulSet or DaemonSet) the Persistent Volume Claim is defined within the Pod specification, as follows:

[[email protected] ~]$ vi create-pod.yaml

kind: Pod
[[email protected] ~]$ packet_write_wait: Connection to 18.205.188.55 port 22: Broken pipe
kind: Pod
apiVersion: v1
metadata:
  name: nfs-pod
spec:
  containers:
    - name: nfs-demo
      image: alpine
      volumeMounts:
      - name: nfs-demo
          mountPath: /data/nfs
      command: ["/bin/sh"]
      args: ["-c", "sleep 500000"]
  volumes:
  - name: nfs-demo
    persistentVolumeClaim:
      claimName: nfs-demo
[[email protected] ~]$ kubectl create -f create-pod.yaml
pod/nfs-pod created

[[email protected] ~]$ kubectl get pods -o wide -n nfs-demo
NAME      READY   STATUS    RESTARTS   AGE   IP              NODE                         NOMINATED NODE   READINESS GATES
nfs-pod   1/1     Running   0          9s    192.168.37.68   ip-10-3-0-143.ec2.internal              

Let’s now create an empty file into the container volume mount path and see if it is has been created on the NFS server.

[[email protected] ~]$ kubectl -n nfs-demo exec nfs-pod touch /data/test-nfs.sh

We can see now, in the NFS server that the file has been properly stored.

[email protected]: ssh -i "dbi.pem" [email protected]
Last login: Tue Nov 19 13:35:18 2019 from 62.91.42.92

       __|  __|_  )
       _|  (     /   Amazon Linux 2 AMI
      ___|\___|___|

https://aws.amazon.com/amazon-linux-2/
16 package(s) needed for security, out of 27 available
Run "sudo yum update" to apply all updates.

[[email protected] ~]$ ls -lrt data/
total 0
-rw-r--r-- 1 root root 0 Nov 19 13:42 test-nfs.sh

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Mehdi Bada
Mehdi Bada

Consultant