Si applica a SUSE Enterprise Storage 7

3 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.

3.1 Provisioning Block Storage #

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

Nota

This sample requires at least one OSD per node, with each OSD located on three 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.

Nota

This example uses the CSI driver, which is the preferred driver going forward for Kubernetes 1.13 and newer. Examples are found in the CSI RBD directory.

Save this StorageClass definition as storageclass.yaml:

apiVersion: ceph.rook.io/v1
kind: CephBlockPool
metadata:
  name: replicapool
  namespace: rook-ceph
spec:
  failureDomain: host
  replicated:
    size: 3
---
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: rook-ceph-block
# Change "rook-ceph" provisioner prefix to match the operator namespace if needed
provisioner: rook-ceph.rbd.csi.ceph.com
parameters:
    # clusterID is the namespace where the rook cluster is running
    clusterID: rook-ceph
    # Ceph pool into which the RBD image shall be created
    pool: replicapool

    # RBD image format. Defaults to "2".
    imageFormat: "2"

    # RBD image features. Available for imageFormat: "2". CSI RBD currently supports only `layering` feature.
    imageFeatures: layering

    # The secrets contain Ceph admin credentials.
    csi.storage.k8s.io/provisioner-secret-name: rook-csi-rbd-provisioner
    csi.storage.k8s.io/provisioner-secret-namespace: rook-ceph
    csi.storage.k8s.io/controller-expand-secret-name: rook-csi-rbd-provisioner
    csi.storage.k8s.io/controller-expand-secret-namespace: rook-ceph
    csi.storage.k8s.io/node-stage-secret-name: rook-csi-rbd-node
    csi.storage.k8s.io/node-stage-secret-namespace: rook-ceph

    # Specify the filesystem type of the volume. If not specified, csi-provisioner
    # will set default as `ext4`. Note that `xfs` is not recommended due to potential deadlock
    # in hyperconverged settings where the volume is mounted on the same node as the osds.
    csi.storage.k8s.io/fstype: ext4

# Delete the rbd volume when a PVC is deleted
reclaimPolicy: Delete

If you have deployed the Rook operator in a namespace other than «rook-ceph», change the prefix in the provisioner to match the namespace you used. For example, if the Rook operator is running in the namespace «my-namespace» the provisioner value should be «my-namespace.rbd.csi.ceph.com».

Create the storage class.

kubectl@adm > kubectl create -f cluster/examples/kubernetes/ceph/csi/rbd/storageclass.yaml

Nota

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.

3.2 Consuming storage: WordPress sample #

In this example, we will create a sample application to consume the block storage provisioned by Rook with the classic WordPress and MySQL apps. Both of these applications will make use of block volumes provisioned by Rook.

Start MySQL and WordPress from the cluster/examples/kubernetes folder:

kubectl@adm > kubectl create -f mysql.yaml
kubectl create -f wordpress.yaml

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

kubectl@adm > kubectl get pvc
NAME             STATUS    VOLUME                                     CAPACITY   ACCESSMODES   AGE
mysql-pv-claim   Bound     pvc-95402dbc-efc0-11e6-bc9a-0cc47a3459ee   20Gi       RWO           1m
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:

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

You should see the WordPress application running.

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

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

Nota

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.

3.3 Consuming the storage: Toolbox #

With the pool that was created above, we can also create a block image and mount it directly in a pod.

3.4 Teardown #

To clean up all the artifacts created by the block-storage demonstration:

kubectl@adm > kubectl delete -f wordpress.yaml
kubectl@adm > kubectl delete -f mysql.yaml
kubectl@adm > kubectl delete -n rook-ceph cephblockpools.ceph.rook.io replicapool
kubectl@adm > kubectl delete storageclass rook-ceph-block

3.5 Advanced Example: Erasure-Coded Block Storage #

If you want to use erasure-coded pools with RBD, your OSDs must use bluestore as their storeType. Additionally, the nodes that will mount the erasure-coded RBD block storage must have Linux kernel 4.11 or above.

This example requires at least three 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 three different OSDs (two dataChunks plus one codingChunk).

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.

3.5.1 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.