Cinder Volumes

Cinder Volumes

This tutorial explains how to mount cinder volumes in containers in Magnum.

For all examples we'll use a previously created volume on OpenStack:

$ openstack volume create --size 2 myvolume

$ openstack volume show myvolume | grep '| id'
| id | 242de616-95a0-4bd7-9bfa-166022509788 |

We'll require the ID of the volume later.

Additional documentation is available in the upstream Magnum guide.

Docker Swarm

We rely on a docker volume driver called rexray for integration in Docker Swarm.

Simply pass rexray as volume driver and the ID of the volume.

$ docker run -it --volume-driver rexray -v 242de616-95a0-4bd7-9bfa-166022509788:/mydata

Kubernetes

Below is an example of a kubernetes application definition.

You can either refer to an existing cinder volume (via its ID):

$ cat nginx-cinder.yaml
apiVersion: v1
kind: Pod
metadata:
  name: web
spec:
  containers:
    - name: web
      image: nginx
      ports:
        - name: web
          containerPort: 80
          hostPort: 8081
          protocol: TCP
      volumeMounts:
        - name: myvolume
          mountPath: "/usr/share/nginx/html"
  volumes:
    - name: myvolume
      cinder:
        # Enter the volume ID below
        volumeID: 242de616-95a0-4bd7-9bfa-166022509788
        fsType: ext4

$ kubectl create -f nginx-cinder.yaml

Or alternatively, rely on dynamic volume provisioning by defining a volume claim.

You can defined multiple StorageClass objects mapping Cinder volume types, as defined here.

In this example we define two StorageClass objects (standard and io1), and create a volume claim for a standard volume of 1GB.

$ cat nginx-cinder.yaml

kind: StorageClass
apiVersion: storage.k8s.io/v1beta1
metadata:
  name: standard
provisioner: kubernetes.io/cinder
parameters:
  type: standard
---
kind: StorageClass
apiVersion: storage.k8s.io/v1beta1
metadata:
  name: io1
provisioner: kubernetes.io/cinder
parameters:
  type: io1
---
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: myclaim
  annotations:
    volume.beta.kubernetes.io/storage-class: standard
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi # pass here the size of the volume
---
apiVersion: v1
kind: Pod
metadata:
  name: web
spec:
  containers:
    - name: web
      image: nginx
      ports:
        - name: web
          containerPort: 80
          hostPort: 8081
          protocol: TCP
      volumeMounts:
        - mountPath: "/usr/share/nginx/html"
          name: mypd
  volumes:
    - name: mypd
      persistentVolumeClaim:
        claimName: myclaim

$ kubectl create -f nginx-cinder.yaml
$ kubectl get pvc
NAME      STATUS    VOLUME                                     CAPACITY   ACCESSMODES   AGE
myclaim   Bound     pvc-e93fc7ad-1ae2-11e7-a49c-02163e018bf2   1Gi        RWO           4s

$ kubectl get pv
NAME                                       CAPACITY   ACCESSMODES   STATUS     CLAIM             REASON    AGE
pvc-e93fc7ad-1ae2-11e7-a49c-02163e018bf2   1Gi        RWO           Bound      default/myclaim             7m

In this case a new cinder volume will be created and attached to the web pod.

Full documentation on storage classes, persistent volume and claims is available here.