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.

NOTE This example requires you to have at least 3 OSDs each on a different node. This is because the replicated.size: 3 will require at least 3 OSDs and as failureDomain setting to host (default), each OSD needs to be on a different nodes.

Save this storage class definition as storageclass.yaml:

  1. apiVersion: ceph.rook.io/v1
  2. kind: CephBlockPool
  3. metadata:
  4.   name: replicapool
  5.   namespace: rook-ceph
  6. spec:
  7.   failureDomain: host
  8.   replicated:
  9.     size: 3
  10. ---
  11. apiVersion: storage.k8s.io/v1
  12. kind: StorageClass
  13. metadata:
  14.    name: rook-ceph-block
  15. provisioner: ceph.rook.io/block
  16. parameters:
  17.   blockPool: replicapool
  18.   # The value of "clusterNamespace" MUST be the same as the one in which your rook cluster exist
  19.   clusterNamespace: rook-ceph
  20.   # Specify the filesystem type of the volume. If not specified, it will use `ext4`.
  21.   fstype: xfs
  22. # Optional, default reclaimPolicy is "Delete". Other options are: "Retain", "Recycle" as documented in https://kubernetes.io/docs/concepts/storage/storage-classes/
  23. reclaimPolicy: Retain

Create the storage class.

  1. kubectl create -f storageclass.yaml

NOTE As specified by Kubernetes, when using the Retain reclaim policy, the ceph RBD images that back up PersistentVolumes will continue to exist even after the PV is deleted, and have to be cleaned up manually using rbd rm.

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 cephblockpools.ceph.rook.io replicapool
  4. kubectl delete storageclass rook-ceph-block

Advanced Example: Erasure Coded Block Storage

If you want to use erasure coded pool with RBD, your OSDs must use bluestore as their storeType. Additionally the nodes that are going to mount the erasure coded RBD block storage must have Linux kernel >= 4.11.

To be able to use an erasure coded pool you need to create two pools (as seen below in the definitions): one erasure coded and one replicated. The replicated pool must be specified as the blockPool parameter. It is used for the metadata of the RBD images. The erasure coded pool must be set as the dataBlockPool parameter below. It is used for the data of the RBD images.

NOTE This example requires you to have at least 3 bluestore OSDs each on a different node. This is because the below erasureCoded chunk settings require at least 3 bluestore OSDs and as failureDomain setting to host (default), each OSD needs to be on a different nodes.

  1. apiVersion: ceph.rook.io/v1
  2. kind: CephBlockPool
  3. metadata:
  4.   name: replicated-metadata-pool
  5.   namespace: rook-ceph
  6. spec:
  7.   failureDomain: host
  8.   replicated:
  9.     size: 3
  10. ---
  11. apiVersion: ceph.rook.io/v1
  12. kind: CephBlockPool
  13. metadata:
  14.   name: ec-data-pool
  15.   namespace: rook-ceph
  16. spec:
  17.   failureDomain: host
  18.   # Make sure you have enough nodes and OSDs running bluestore to support the replica size or erasure code chunks.
  19.   # For the below settings, you need at least 3 OSDs on different nodes (because the `failureDomain` is `host` by default).
  20.   erasureCoded:
  21.     dataChunks: 2
  22.     codingChunks: 1
  23. ---
  24. apiVersion: storage.k8s.io/v1
  25. kind: StorageClass
  26. metadata:
  27.    name: rook-ceph-block
  28. provisioner: ceph.rook.io/block
  29. parameters:
  30.   blockPool: replicated-metadata-pool
  31.   dataBlockPool: ec-data-pool
  32.   # Specify the namespace of the rook cluster from which to create volumes.
  33.   # If not specified, it will use `rook` as the default namespace of the cluster.
  34.   # This is also the namespace where the cluster will be
  35.   clusterNamespace: rook-ceph
  36.   # Specify the filesystem type of the volume. If not specified, it will use `ext4`.
  37.   fstype: xfs

(These definitions can also be found in the storageclass-ec.yaml file)