Kubernetes volume expansion with Ceph RBD CSI driver

Kubernetes, Ceph

In this post I will show you how can you use CEPH RBD CSI driver as persistent storage end enable volume expansion on Kubernetes.

Parts of the Kubernetes series

Firt we need to install the csi-resizer. This is a sidecar container that watches Kubernetes PersistentVolumeClaims objects and triggers controller side expansion operation against a CSI endpoint

kubens ceph-csi-rbd
wget https://raw.githubusercontent.com/kubernetes-csi/external-resizer/master/deploy/kubernetes/rbac.yaml

# chaneg namespace to your namespace in my case ceph-csi-rbd
nano rbac.yaml

kubectl apply -f rbac.yaml
kubectl apply -f https://raw.githubusercontent.com/kubernetes-csi/external-resizer/master/deploy/kubernetes/deployment.yaml

Create or edit a StorageClass with the peccary parameters like (csi.storage.k8s.io/controller-expand-secret-namespace: default,csi.storage.k8s.io/controller-expand-secret-name: csi-rbd-secret,allowVolumeExpansion: true):

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: k8s-etc
  annotations:
    storageclass.kubernetes.io/is-default-class: 'true'
provisioner: rbd.csi.ceph.com
parameters:
  pool: k8s-etc
  clusterID: e285a458-7c95-4187-8129-fbd6c370c537
  imageFeatures: layering
  csi.storage.k8s.io/fstype: ext4
  csi.storage.k8s.io/provisioner-secret-namespace: default
  csi.storage.k8s.io/provisioner-secret-name: csi-rbd-secret
  csi.storage.k8s.io/node-stage-secret-namespace: default
  csi.storage.k8s.io/node-stage-secret-name: csi-rbd-secret
  csi.storage.k8s.io/controller-expand-secret-namespace: default
  csi.storage.k8s.io/controller-expand-secret-name: csi-rbd-secret
volumeBindingMode: Immediate
reclaimPolicy: Delete
allowVolumeExpansion: true
mountOptions:
  - discard

Create demo app for expansion:

nano testclaim.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: test-claim
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi

nano testpod.yaml
apiVersion: v1
kind: ReplicationController
metadata:
  name: nginx
spec:
  replicas: 1
  selector:
    app: nginx
  template:
    metadata:
      name: nginx
      labels:
        app: nginx
    spec:
#      securityContext:
#        fsGroupChangePolicy: ReadWriteOnceWithFSType
      containers:
      - name: nginx
        image: nginx
        ports:
        - containerPort: 80
        volumeMounts:
          - mountPath: /var/lib/www/html
            name: mypvc
      volumes:
        - name: mypvc
          persistentVolumeClaim:
            claimName: test-claim

kubectl apply -f testclaim.yaml
kubectl apply -f testpod.yaml

kgp
NAME          READY   STATUS    RESTARTS   AGE
nginx-qsw7x   1/1     Running   0          115

kubectl exec -ti nginx-qsw7x -- df -kh|grep var
/dev/rbd7                974M   24K  958M   1% /var/lib/www/html

kgpvc
NAME         STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
test-claim   Bound    pvc-da8019f5-cf01-4ede-8e36-90dd8a79564b   1Gi        RWO            k8s-etc     11m

Now we can change the size of the pvc and the operator will extend teh pv fo it automatically:

kubectl patch pvc test-claim -p '{"spec": {"resources": {"requests": {"storage": "5Gi"}}}}'

kgpvc
NAME         STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
test-claim   Bound    pvc-da8019f5-cf01-4ede-8e36-90dd8a79564b   5Gi        RWO            k8s-etc     11m

kubectl exec -ti nginx-qsw7x -- df -kh|grep var
/dev/rbd7                4.9G   24K  4.9G   1% /var/lib/www/html