Block Storage

Block storage allows you to mount storage to a single pod. This example shows how to build a simple, multi-tier web application on Kubernetes using persistent volumes enabled by Rook.

Prerequisites

This guide assumes you have created a Rook cluster as explained in the main Quickstart guide.

Provision Storage

Before Rook can start provisioning storage, a StorageClass and its storage pool need to be created. This is needed for Kubernetes to interoperate with Rook for provisioning persistent volumes. For more options on pools, see the documentation on creating storage pools.

Save this storage class definition as storageclass.yaml:

  1. apiVersion: ceph.rook.io/v1beta1
  2. kind: Pool
  3. metadata:
  4.   name: replicapool
  5.   namespace: rook-ceph
  6. spec:
  7.   replicated:
  8.     size: 3
  9. ---
  10. apiVersion: storage.k8s.io/v1
  11. kind: StorageClass
  12. metadata:
  13.    name: rook-ceph-block
  14. provisioner: ceph.rook.io/block
  15. parameters:
  16.   pool: replicapool
  17.   #The value of "clusterNamespace" MUST be the same as the one in which your rook cluster exist
  18.   clusterNamespace: rook-ceph

Create the storage class.

  1. kubectl create -f storageclass.yaml

Consume the storage: Wordpress sample

We create a sample app to consume the block storage provisioned by Rook with the classic wordpress and mysql apps. Both of these apps will make use of block volumes provisioned by Rook.

Start mysql and wordpress from the cluster/examples/kubernetes folder:

  1. kubectl create -f mysql.yaml
  2. kubectl create -f wordpress.yaml

Both of these apps create a block volume and mount it to their respective pod. You can see the Kubernetes volume claims by running the following:

  1. $ kubectl get pvc
  2. NAME             STATUS    VOLUME                                     CAPACITY   ACCESSMODES   AGE
  3. mysql-pv-claim   Bound     pvc-95402dbc-efc0-11e6-bc9a-0cc47a3459ee   20Gi       RWO           1m
  4. wp-pv-claim      Bound     pvc-39e43169-efc1-11e6-bc9a-0cc47a3459ee   20Gi       RWO           1m

Once the wordpress and mysql pods are in the Running state, get the cluster IP of the wordpress app and enter it in your browser:

  1. $ kubectl get svc wordpress
  2. NAME        CLUSTER-IP   EXTERNAL-IP   PORT(S)        AGE
  3. wordpress   10.3.0.155   <pending>     80:30841/TCP   2m

You should see the wordpress app running.

If you are using Minikube, the Wordpress URL can be retrieved with this one-line command:

  1. echo http://$(minikube ip):$(kubectl get service wordpress -o jsonpath='{.spec.ports[0].nodePort}')

NOTE: When running in a vagrant environment, there will be no external IP address to reach wordpress with. You will only be able to reach wordpress via the CLUSTER-IP from inside the Kubernetes cluster.

Consume the storage: Toolbox

With the pool that was created above, we can also create a block image and mount it directly in a pod. See the Direct Block Tools topic for more details.

Teardown

To clean up all the artifacts created by the block demo:

  1. kubectl delete -f wordpress.yaml
  2. kubectl delete -f mysql.yaml
  3. kubectl delete -n rook-ceph pool replicapool
  4. kubectl delete storageclass rook-ceph-block