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

Deploy Database with a Persistent Volume Claim

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

To monitor resources for this lab, open a new terminal and start watching for relevant objecting using the following command.


watch kubectl get pods,pvc,pv,storageclasses

We will call the terminal where you are running the above command as your Monitoring Screen.

  • Observe and note if 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: 200Mi
  storageClassName: local-path

if you using a KIND bases environment, set StorageClassName to "standard" instead of "local-path" in the above file. In case of KIND environment, no further configuration of Storageclass/Provisioner is needed.

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 Storage Provisioner in kubernetes

Skip this step is you are using KIND based environment.

Launch a local path provisioner using the following command,

kubectl apply -f https://raw.githubusercontent.com/rancher/local-path-provisioner/master/deploy/local-path-storage.yaml

This will create all the objects required to setup a local-path provisioner. At this time, you should also see storageclass created for local-path on your monitoring screen.

kubectl get storageclass
kubectl get pods
kubectl logs -f local-path-provisioner-xxxx -n local-path-storage

Validate

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 in action.

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 volume of size 20Mi 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 learnt to setup dynamic provisioning provisioner with Storage Classes, Provisioners and PersistentVolumeClaims.