Volume

Volumes are one of the ways you can store data. Magnum allows Kubernetes to use Cinder Volumes as Kubernetes Volumes, so that you can store data persistently.

Create a StorageClass

1. Create a default StorageClass. You only need to do this once per cluster. This defines which availability zone you want to create volumes in. Remember to replace <availability-zone> with the availability zone where you have volume quota. Create the following as storageclass.yaml.

   apiVersion: storage.k8s.io/v1
   kind: StorageClass
   metadata:
     name: default
     annotations:
       storageclass.kubernetes.io/is-default-class: "true"
   parameters:
     availability: <availability-zone>
   provisioner: cinder.csi.openstack.org
   

2. Apply the yaml

   kubectl apply -f storageclass.yaml
   

Create a PersistentVolumeClaim

1. Create a PersistentVolumeClaim. On Nectar Cloud, this creates a volume backed by Cinder. Create the following as myvol.yaml.

   kind: PersistentVolumeClaim
   apiVersion: v1
   metadata:
     name: myvol
     namespace: default
   spec:
     accessModes:
     - ReadWriteOnce
     resources:
       requests:
         storage: 3Gi
   

2. Apply the yaml

   kubectl apply -f myvol.yaml
   

3. You should be able to see the PersistentVolume created. (You might need to wait a few minutes for it to be ready)

   kubectl get pvc
   kubectl get pv
   

Create a Pod

1. Create a nginx Pod that uses the PVC as a persistent volume. Create the following as nginxcinder.yaml.

   apiVersion: v1
   kind: Pod
   metadata:
     name: nginxcinder
     labels:
       app: nginxcinder
   spec:
     containers:
       - name: nginxcinder
         image: nginx
         volumeMounts:
           - name: html-volume
             mountPath: "/usr/share/nginx/html"
     volumes:
       - name: html-volume
         persistentVolumeClaim:
           claimName: myvol
   

2. Apply the yaml

   kubectl apply -f nginxcinder.yaml
   

Writing index page for nginx

In the previous example, we have mounted a blank new volume to our pod.

Now, we want to write data to volume for nginx to service.

1. Open up a shell to the pod

   kubectl exec -it pod/nginxcinder -- /bin/bash
   

2. Use the following command to create the default index page.

   root@nginxcinder:/# echo "THIS IS MY PAGE" > /usr/share/nginx/html/index.html
   

3. Exit the pod cli

   root@nginxcinder:/# exit
   

Redirect loadbalancer

Direct your loadbalancer to your new pod. We can do this easily by updating the label.

1. Edit nginxservice.yaml and make the following changes

   apiVersion: v1
   kind: Service
   metadata:
     name: nginxservice
   spec:
     ports:
     - port: 80
       targetPort: 80
       protocol: TCP
     selector:
       #run: webserver
       app: nginxcinder
     type: LoadBalancer
   

2. Run kubectl apply -f nginxservice.yaml

3. Refresh the URL pointing to your loadbalancer. You should now see your custom page

Checking for persistency

1. If you delete the pod and recreate it, the same content should still be available. This shows that the volume is not tied to the lifetime of the pod.

   kubectl delete pod nginxcinder
   kubectl apply -f nginxcinder.yaml
   

Clean up

1. Delete the pod and PersistentVolume when you are done

   kubectl delete pod nginxcinder
   kubectl delete pvc myvol
   

More information

For more information, refer to:

• Volumes