Block Storage

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

Prerequisites

This guide assumes a Rook cluster as explained in the Quickstart.

Provision Storage

Before Rook can provision storage, a StorageClass and CephBlockPool need to be created. This will allow Kubernetes to interoperate with Rook when provisioning persistent volumes.

NOTE: This sample requires at least 1 OSD per node, with each OSD located on 3 different nodes.

Each OSD must be located on a different node, because the failureDomain is set to host and the replicated.size is set to 3.

NOTE: This example uses the CSI driver, which is the preferred driver going forward for K8s 1.13 and newer. Examples are found in the CSI RBD directory. For an example of a storage class using the flex driver (required for K8s 1.12 or earlier), see the Flex Driver section below, which has examples in the flex directory.

Save this StorageClass 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. # Change "rook-ceph" provisioner prefix to match the operator namespace if needed
  16. provisioner: rook-ceph.rbd.csi.ceph.com
  17. parameters:
  18.     # clusterID is the namespace where the rook cluster is running
  19.     clusterID: rook-ceph
  20.     # Ceph pool into which the RBD image shall be created
  21.     pool: replicapool
  23.     # RBD image format. Defaults to "2".
  24.     imageFormat: "2"
  26.     # RBD image features. Available for imageFormat: "2". CSI RBD currently supports only `layering` feature.
  27.     imageFeatures: layering
  29.     # The secrets contain Ceph admin credentials.
  30.     csi.storage.k8s.io/provisioner-secret-name: rook-csi-rbd-provisioner
  31.     csi.storage.k8s.io/provisioner-secret-namespace: rook-ceph
  32.     csi.storage.k8s.io/node-stage-secret-name: rook-csi-rbd-node
  33.     csi.storage.k8s.io/node-stage-secret-namespace: rook-ceph
  35.     # Specify the filesystem type of the volume. If not specified, csi-provisioner
  36.     # will set default as `ext4`.
  37.     csi.storage.k8s.io/fstype: xfs
  39. # Delete the rbd volume when a PVC is deleted
  40. reclaimPolicy: Delete

If you’ve deployed the Rook operator in a namespace other than “rook-ceph” as is common change the prefix in the provisioner to match the namespace you used. For example, if the Rook operator is running in “rook-op” the provisioner value should be “rook-op.rbd.csi.ceph.com”.

Create the storage class.

  1. kubectl create -f cluster/examples/kubernetes/ceph/csi/rbd/storageclass.yaml

NOTE: As specified by Kubernetes, when using the Retain reclaim policy, any Ceph RBD image that is backed by a PersistentVolume will continue to exist even after the PersistentVolume has been deleted. These Ceph RBD images will need 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

Flex Driver

To create a volume based on the flex driver instead of the CSI driver, see the following example of a storage class. Make sure the flex driver is enabled over Ceph CSI. For this, you need to set ROOK_ENABLE_FLEX_DRIVER to true in your operator deployment in the operator.yaml file. The pool definition is the same as for the CSI driver.

  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
  24. # Optional, if you want to add dynamic resize for PVC. Works for Kubernetes 1.14+
  25. # For now only ext3, ext4, xfs resize support provided, like in Kubernetes itself.
  26. allowVolumeExpansion: true

Create the pool and storage class using kubectl:

  1. kubectl create -f cluster/examples/kubernetes/ceph/flex/storageclass.yaml

Continue with the example above for the wordpress application.

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.

NOTE: This example requires at least 3 bluestore OSDs, with each OSD located on a different node.

The OSDs must be located on different nodes, because the failureDomain is set to host and the erasureCoded chunk settings require at least 3 different OSDs (2 dataChunks + 1 codingChunks).

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.

NOTE: This example requires at least 3 bluestore OSDs, with each OSD located on a different node.

The OSDs must be located on different nodes, because the failureDomain is set to host and the erasureCoded chunk settings require at least 3 different OSDs (2 dataChunks + 1 codingChunks).

Erasure Coded CSI Driver

The erasure coded pool must be set as the dataPool parameter in storageclass-ec.yaml It is used for the data of the RBD images.

Erasure Coded Flex Driver

The erasure coded pool must be set as the dataBlockPool parameter in storageclass-ec.yaml. It is used for the data of the RBD images.