Dynamic Storage Provisioning

This tutorial explains how kubernetes storage works and the complete workflow for the dynamic provisioning. The topics include

  • Storage Classes
  • PersistentVolumeClaim
  • persistentVolume
  • Provisioner

Pre Reading :

Concepts

kubernetes Storage Concepts

Redploy db with a a reference to PVC

Lets begin by redeploying the db deployment, this time by configuring it to refer to the persistentVolumeClaim

file: db-deploy-pvc.yaml

...
spec:
   containers:
   - image: postgres:9.4
     imagePullPolicy: Always
     name: db
     ports:
     - containerPort: 5432
       protocol: TCP
     #mount db-vol to postgres data path
     volumeMounts:
     - name: db-vol
       mountPath: /var/lib/postgresql/data
   #create a volume with pvc
   volumes:
   - name: db-vol
     persistentVolumeClaim:
       claimName: db-pvc

Apply db-deploy-pcv.yaml as

kubectl apply -f db-deploy-pvc.yaml

kubectl get pod -o wide --selector='role=db'

kubectl get pvc,pv
  • Observe and note which host the pod for db is launched.
  • What state is it in ? why?
  • Has the persistentVolumeClaim been bound to a persistentVolume ? Why?

Creating a Persistent Volume Claim

switch to project directory

cd k8s-code/projects/instavote/dev/

Create the following file with the specs below

file: db-pvc.yaml

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: db-pvc
spec:
  accessModes:
    - ReadWriteOnce
  volumeMode: Filesystem
  resources:
    requests:
      storage: 2Gi
  storageClassName: nfs

create the Persistent Volume Claim and validate

kubectl get pvc


kubectl apply -f db-pvc.yaml

kubectl get pvc,pv

  • Is persistentVolumeClaim created ? Why ?
  • Is persistentVolume created ? Why ?
  • Is the persistentVolumeClaim bound with a persistentVolume ?

Set up NFS Provisioner in kubernetes

Change into nfs provisioner installation dir

cd k8s-code/storage

Deploy nfs-client provisioner.

kubectl apply -f nfs

This will create all the objects required to setup a nfs provisioner. It would be launched with Statefulsets. Read the official documentation on Statefulsets to understand how its differnt than deployments.

kubectl get storageclass
kubectl get pods
kubectl logs -f nfs-provisioner-0

Now, observe the output of the following commands,

kubectl get pvc,pv
kubectl get pods
  • Do you see pvc bound to pv ?
  • Do you see the pod for db running ?

Observe the dynamic provisioning, go to the host which is running nfs provisioner and look inside /srv path to find the provisioned volume.

Fix result app after recreating db

Result app which connects with the db looses the connection and ceases to work after db is redeployed. This is a bug in the application. However, to do a quick fix, redeploy result app as

kubectl rollout restart deploy result

This would recreate the pods for result app and you should see it working again.

Nano Project

Similar to postgres which mounts the data at /var/lib/postgresql/data and consumes it to store the database files, Redis creates and stores the file at /data path. Your task is to have a nfs volume of size 200Mi created and mounted at /data for the redis container.

You could follow these steps to complete this task

  • create a pvc by name redis
  • create a volume in the pod spec with type persistentVolumeClaim. Call is redis-data
  • add volumeMounts to the container spec (part of the same deployment file) running redis and have it mount redis-data volume created in the pod spec above.

Summary

In this lab, you not only setup dynamic provisioning using NFS, but also learnt about statefulsets as well as rbac policies applied to the nfs provisioner.