Minikube - Persistence Volume

One of the important concepts in Kubernetes is to define persistence volumes to retain the data when nodes get deleted or restarted. I have not studied the methods for persistent volume in detail, but to fulfill my requirements, I found choosing persistent volume with NFS(network file system) to be very useful, so that I can assign an external volume mounted as NFS as a persistent volume in Kubernetes' pods. 

Some of the mechanisms of the persistent volume are 

1) Hostpath => Volume in the host system of the node. It is destroyed when a node is restarted or removed. 

2) Local => accessible to pods in  a node (any mounted partition can be assigned)

3) NFS => This one is the best for me. I can use any system in the network and mount the network file system (NFS) to use as a persistent volume. 

NFS Persistent Volume 

 https://kubernetes.io/docs/concepts/storage/volumes/#local 

In summary, we need to install nfs-kernel-server on the host system.

sudo apt update

sudo apt install nsf-kernel-server

Then we create a shared directory

sudo mkdir /Backup/k8s-volume

cd /Backup/k8s-volume

NFS will translate any root operations on the client to the nobody:nogroup credentials as a security measure. Therefore, you need to change the directory ownership to match those credentials.

sudo chown nobody:nogroup /Backup/k8s-volume

sudo service nfs-kernel-server restart

We now want to config NFS exports on the host

The following line in /etc/exports will suffice 

/Backup/k8s_volume *(rw,sync,no_subtree_check,no_root_squash,no_all_squash,insecure)

The exported volume can be mounted anywhere from the network. So even if the nodes got destroyed or restarted, we have persistent data safe in the network system. 

sudo exportfs -rav  (exports all filesystem paths)

sudo exportfs -v  (verify)

Finally, restart the server:

sudo systemctl restart nfs-kernel-server

Now the server is running. If the server is using some firewall techniques, we have to allow the NFS port 2049. 

Command to verify (from client)

sudo mount -t nfs <server(ip/hostname)>:/Backup/k8s_volume /mnt

The files will be mounted into /mnt folder 

To unmount

sudo umount /mnt

Note: There is much other information in the link given above. For Kubernetes, this will be enough.

Now let's create pv.yaml file with NFS persistent volume:

apiVersion: v1

kind: PersistentVolume

metadata:

name: persistent-volume

labels:

type: nfs

app: k8s_volume

spec:

capacity:

storage: 10Gi

volumeMode: Filesystem

accessModes:

- ReadWriteMany

storageClassName: manual

#hostPath:

# path: /Backup/temp/volumes

nfs:

path: /Backup/k8s_volume

server: 192.168.x.xxx

readOnly: false

kubectl apply -f pv.yaml

kubectl get pv 

The result shows the create persistent volume. We can then allocate the volume needed for pods, which is called "persistent volume claim" or pvc. For example: pvc.yaml

apiVersion: v1

kind: PersistentVolumeClaim

metadata:

name: postgres-volume-claim

labels:

app: k8s_volume

spec:

storageClassName: manual

accessModes:

- ReadWriteMany

resources:

requests:

storage: 1Gi  

Note the app name in pv.yaml and pvc.yaml is the same so that PVC knows from where the volume to claim is.