Ceph storage

Many workloads that you may want to run on your Kubernetes cluster will require some form of available storage. This guide will help you deploy Charmed Kubernetes with Ceph container storage support. Available storage backends include ceph-xfs, ceph-ext4, and cephfs.

Deploying Ceph and Charmed Kubernetes

In this section, we’ll create a small Ceph cluster along with a basic Charmed Kubernetes environment that includes Ceph CSI support.

Deploy Ceph

Start by deploying three Ceph monitor nodes:

juju deploy -n 3 ceph-mon

…and then add three storage nodes. For the storage nodes, we will specify additional deployment parameters by using the --storage flag:

juju deploy -n 3 ceph-osd --storage osd-devices=32G,2 --storage osd-journals=8G,1

The storage nodes above will have two 32GB devices for storage and 8GB for journaling. As we have asked for 3 machines, this means a total of 192GB of storage and 24GB of journal space. The storage comes from whatever the default storage class is for the cloud (e.g., on AWS this will be EBS volumes).

juju integrate ceph-osd ceph-mon

<span class="p-notification__title">Note:</span>
<p class="p-notification__message">For more on how Juju makes use of storage, please see the relevant <a href="https://juju.is/docs/juju/manage-storage">Juju documentation</a></p>

Deploy Charmed Kubernetes with Ceph CSI

Ceph CSI creates various Kubernetes resources, including pods. Therefore it requires the kubernetes-control-plane application to run in privileged mode. Create a suitable environment as follows:

juju deploy charmed-kubernetes
juju config kubernetes-control-plane allow-privileged=true

juju deploy ceph-csi
juju deploy ceph-fs
juju config ceph-csi cephfs-enable=True

Now add the relevant Ceph integrations:

juju integrate ceph-csi:kubernetes kubernetes-control-plane:juju-info
juju integrate ceph-csi:ceph-client ceph-mon:client
juju integrate ceph-fs:ceph-mds ceph-mon:mds

Verify things are working

Check the Charmed Kubernetes cluster to verify Ceph cluster resources are available. Running:

juju ssh kubernetes-control-plane/leader -- kubectl get sc,po --namespace default

…should return output similar to:

NAME                                             PROVISIONER           RECLAIMPOLICY   VOLUMEBINDINGMODE   ALLOWVOLUMEEXPANSION   AGE
storageclass.storage.k8s.io/ceph-ext4            rbd.csi.ceph.com      Delete          Immediate           true                   142m
storageclass.storage.k8s.io/ceph-xfs (default)   rbd.csi.ceph.com      Delete          Immediate           true                   142m
storageclass.storage.k8s.io/cephfs               cephfs.csi.ceph.com   Delete          Immediate           true                   127m

NAME                                               READY   STATUS    RESTARTS   AGE
pod/csi-cephfsplugin-4gs22                         3/3     Running   0          127m
pod/csi-cephfsplugin-ljfw9                         3/3     Running   0          127m
pod/csi-cephfsplugin-mlbdx                         3/3     Running   0          127m
pod/csi-cephfsplugin-provisioner-9f479bcc4-48v8f   5/5     Running   0          127m
pod/csi-cephfsplugin-provisioner-9f479bcc4-92bt6   5/5     Running   0          127m
pod/csi-cephfsplugin-provisioner-9f479bcc4-hbb82   5/5     Running   0          127m
pod/csi-cephfsplugin-wlp2w                         3/3     Running   0          127m
pod/csi-cephfsplugin-xwdb2                         3/3     Running   0          127m
pod/csi-rbdplugin-b8nk8                            3/3     Running   0          142m
pod/csi-rbdplugin-bvqwn                            3/3     Running   0          142m
pod/csi-rbdplugin-provisioner-85dc49c6c-9rckg      7/7     Running   0          142m
pod/csi-rbdplugin-provisioner-85dc49c6c-f6h6k      7/7     Running   0          142m
pod/csi-rbdplugin-provisioner-85dc49c6c-n47fx      7/7     Running   0          142m
pod/csi-rbdplugin-vm25h                            3/3     Running   0          142m

If you have installed Helm, you can then add a chart to verify the persistent volume is automatically created for you:

helm install stable/phpbb
kubectl get pvc

…which should return output similar to:

NAME                            STATUS    VOLUME                 CAPACITY   ACCESS MODES   STORAGECLASS   AGE
calling-wombat-phpbb-apache     Bound     pvc-b1d04079a4bd11e8   1Gi        RWO            ceph-xfs       34s
calling-wombat-phpbb-phpbb      Bound     pvc-b1d1131da4bd11e8   8Gi        RWO            ceph-xfs       34s
data-calling-wombat-mariadb-0   Bound     pvc-b1df7ac9a4bd11e8   8Gi        RWO            ceph-xfs       34s

Warning: Removal

When the ceph-csi charm is removed, it will not clean up Ceph pools that were created when the relation with ceph-mon:client was joined. If you wish to remove ceph pools, use the delete-pool action on a ceph-mon unit.

Conclusion

Now you have a Ceph cluster integrated with your Charmed Kubernetes cluster. From here you can install any of the things that require storage out of the box.