Persistent volumes can be used to store stateful/persistent data, this means that when a pods is replaced its successor will still have the data available. This can be used when you want to run persistent databases in pods and/or when you want to share data between different pods.
In this lab we will make a persistent volume that we fill with images, those images will then be served by our application (pods).
Create a namespace for this lab:
kubectl create ns lab-09
---
namespace "lab-09" created
First we will need to ssh into the minikube instance.
minikube ssh
When you are in the minikube instance make sure that you are root. Otherwise you might not be have permission to create the required directories and/or files:
sudo su -
Now we need to create a directory to store our images.
mkdir -p /mnt/data/images
Let's download a couple of images into our persistent images directory:
curl -so /mnt/data/images/meme1.jpeg https://raw.githubusercontent.com/gluobe/cloud-native-track-kubernetes/master/lab-09/images/meme1.jpeg
curl -so /mnt/data/images/meme2.jpeg https://raw.githubusercontent.com/gluobe/cloud-native-track-kubernetes/master/lab-09/images/meme2.jpeg
curl -so /mnt/data/images/meme3.jpeg https://raw.githubusercontent.com/gluobe/cloud-native-track-kubernetes/master/lab-09/images/meme3.jpeg
curl -so /mnt/data/images/meme4.jpeg https://raw.githubusercontent.com/gluobe/cloud-native-track-kubernetes/master/lab-09/images/meme4.jpeg
curl -so /mnt/data/images/meme5.jpeg https://raw.githubusercontent.com/gluobe/cloud-native-track-kubernetes/master/lab-09/images/meme5.jpeg
Now exit the minikube instance.
exit
exit
In this task we are going to create the persistent volume. This will put the
volume in a Available state. It's not yet bound to a persistent volume claim
at this point. Keep in mind that a persistent volume is not namespaced!
Create a file lab-09-pv.yml with the following content.
kind: PersistentVolume
apiVersion: v1
metadata:
name: lab-09-volume
labels:
type: local
spec:
storageClassName: manual
capacity:
storage: 1Gi
accessModes:
- ReadOnlyMany
hostPath:
path: "/mnt/data/images"
You can now create the persistent volume with the kubectl command. It will look like this.
kubectl apply -f lab-09-pv.yml
---
persistentvolume "lab-09-volume" created
At this point the persistent volume is created. Be sure that it is by using the get command.
kubectl get pv
---
NAME CAPACITY ACCESSMODES RECLAIMPOLICY STATUS CLAIM STORAGECLASS REASON AGE
lab-09-volume 1Gi ROX Retain Available manual 23s
Now we need to create the claim for this persistent volume. This way we can bind
the persistent volume claim to a deployment. First we need to create the file
lab-09-pvc.yml with the following content.
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
name: lab-09-claim
spec:
storageClassName: manual
accessModes:
- ReadOnlyMany
resources:
requests:
storage: 1Gi
And apply it with the following command.
kubectl apply -f lab-09-pvc.yml -n lab-09
---
persistentvolumeclaim/lab-09-claim created
You can confirm that it is created with the following command.
kubectl get pvc -n lab-09
---
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
lab-09-claim Bound lab-09-volume 1Gi ROX manual 28s
Now we are able to use the PersistentVolumeClaim in a pod. The following steps will show you how you can do this.
First we need to create a file that describes our pod. This will be
lab-09-deployment.yml with the following content.
apiVersion: apps/v1
kind: Deployment
metadata:
name: meme-persistent
labels:
app: meme-persistent
spec:
replicas: 3
selector:
matchLabels:
app: meme-persistent
template:
metadata:
labels:
app: meme-persistent
spec:
volumes:
- name: lab-09-volume
persistentVolumeClaim:
claimName: lab-09-claim
containers:
- name: meme-persistent
image: gluobe/meme-persistent:v1
ports:
- containerPort: 80
volumeMounts:
- mountPath: "/var/www/html/images"
name: lab-09-volume
Apply the file with the kubectl command:
kubectl create -f lab-09-deployment.yml -n lab-09
---
deployment.apps/meme-persistent created
Be sure that the pods are running.
kubectl get pods -n lab-09
---
meme-persistent-84cdc97446-dc2v4 1/1 Running 0 31s
meme-persistent-84cdc97446-dh59c 1/1 Running 0 31s
meme-persistent-84cdc97446-tq8h8 1/1 Running 0 31s
Create a service to access the application, create a file lab-09-service.yml
with the content below:
kind: Service
apiVersion: v1
metadata:
name: meme-persistent
spec:
selector:
app: meme-persistent
ports:
- protocol: TCP
port: 80
targetPort: 80
type: NodePort
Apply the file:
kubectl apply -f lab-09-service.yml -n lab-09
---
service/meme-persistent created
Check the application:
minikube service meme-persistent -n lab-09
When you refresh the page you should see that again the avatar changes (there are three pods), but the images remain the same (the PHP script will simply show all the images from the persistent volume directory).
You can download one additional image and this should instantly be available on all the pods:
minikube ssh
Make sure you are root:
sudo su -
Download an additional image:
curl -so /mnt/data/images/kubernetes.jpeg https://raw.githubusercontent.com/gluobe/cloud-native-track-kubernetes/master/lab-09/images/kubernetes.png
Refresh your browser to see the new image.
Clean up the namespace for this lab:
kubectl delete ns lab-09
---
namespace "lab-09" deleted
NOTE: we have now deleted our namespace, but as our persistent volume is not namespaced it still exists. So even if you deleted your application your data will still be available. If you are sure you no longer need your data follow the steps below to clean up your persistent volume (and its data)
To delete the persistent volume object (this will not delete any data!):
kubectl delete -f lab-09-pv.yml
To delete the actual data:
minikube ssh
sudo su -
rm -rf /mnt/data/