Overview

This topic provides an end-to-end example of using an existing Ceph cluster as an OpenShift Container Platform dynamic persistent store. It is assumed that a working Ceph cluster is already set up. If not, consult the Overview of Red Hat Ceph Storage.

Persistent Storage Using Ceph Rados Block Device provides an explanation of persistent volumes (PVs), persistent volume claims (PVCs), and how to use Ceph Rados Block Device (RBD) as persistent storage.

All oc …​ commands are executed on the OpenShift Container Platform master host.

Installing the ceph-common Package

The ceph-common library must be installed on all schedulable OpenShift Container Platform nodes:

The OpenShift Container Platform all-in-one host is not often used to run pod workloads and, thus, is not included as a schedulable node.

# yum install -y ceph-common

Create Pool for Dynamic Volumes

It is recommended that you create a pool for your dynamic volumes to live in.

Using the default pool of RBD is an option, but not recommended.

From a Ceph administrator or MON node, create a new pool for dynamic volumes:

$ ceph osd pool create kube 1024
$ ceph auth get-or-create client.kube mon 'allow r' osd 'allow class-read object_prefix rbd_children, allow rwx pool=kube' -o ceph.client.kube.keyring

Creating the Ceph Secret

  1. Run the ceph auth get-key command on a Ceph MON node to display the key value for the client.admin user:

    Ceph Secret Definition
    apiVersion: v1
    kind: Secret
    metadata:
      name: ceph-secret
      namespace: kube-system
    data:
      key: QVFBOFF2SlZheUJQRVJBQWgvS2cwT1laQUhPQno3akZwekxxdGc9PQ== (1)
    type: kubernetes.io/rbd (2)
    1 This base64 key is generated on one of the Ceph MON nodes using the ceph auth get-key client.admin | base64 command, then copying the output and pasting it as the secret key’s value.
    2 This is required for Ceph RBD to work with dynamic provisioning.
  2. Save the secret definition to a file, for example ceph-secret.yaml, then create the secret:

    $ oc create -f ceph-secret.yaml
    secret "ceph-secret" created
  3. Verify that the secret was created:

    # oc get secret ceph-secret
    NAME          TYPE                DATA      AGE
    ceph-secret   kubernetes.io/rbd   1         5d

Creating the Ceph User Secret

  1. Run the ceph auth get-key command on a Ceph MON node to display the key value for the client.kube user:

    Ceph Secret Definition
    apiVersion: v1
    kind: Secret
    metadata:
      name: ceph-user-secret
      namespace: default
    data:
      key: QVFCbEV4OVpmaGJtQ0JBQW55d2Z0NHZtcS96cE42SW1JVUQvekE9PQ== (1)
    type: kubernetes.io/rbd (2)
    1 This base64 key is generated on one of the Ceph MON nodes using the ceph auth get-key client.kube | base64 command, then copying the output and pasting it as the secret key’s value.
    2 This is required for Ceph RBD to work with dynamic provisioning.
  2. Save the secret definition to a file, for example ceph-user-secret.yaml, then create the secret:

    $ oc create -f ceph-user-secret.yaml
    secret "ceph-user-secret" created
  3. Verify that the secret was created:

    # oc get secret ceph-user-secret
    NAME               TYPE                DATA      AGE
    ceph-user-secret   kubernetes.io/rbd   1         5d

Ceph RBD Dynamic Storage Class

  1. Create a storage class to for your dynamic volumes.

    ceph-storageclass.yaml
    apiVersion: storage.k8s.io/v1beta1
    kind: StorageClass
    metadata:
      name: dynamic
      annotations:
         storageclass.beta.kubernetes.io/is-default-class: "true"
    provisioner: kubernetes.io/rbd
    parameters:
      monitors: 192.168.1.11:6789,192.168.1.12:6789,192.168.1.13:6789  (1)
      adminId: admin  (2)
      adminSecretName: ceph-secret  (3)
      adminSecretNamespace: kube-system  (4)
      pool: kube  (5)
      userId: kube  (6)
      userSecretName: ceph-user-secret (7)
    1 Ceph monitors, comma delimited. It is required.
    2 Ceph client ID that is capable of creating images in the pool. Default is admin.
    3 Secret Name for adminId. It is required. The provided secret must have type kubernetes.io/rbd.
    4 The namespace for adminSecret. Default is default.
    5 Ceph RBD pool. Default is rbd, but that value is not recommended.
    6 Ceph client ID that is used to map the Ceph RBD image. Default is the same as adminId.
    7 The name of Ceph Secret for userId to map Ceph RBD image. It must exist in the same namespace as PVCs. It is required unless its set as the default in new projects.

Creating the Persistent Volume Claim

A persistent volume claim (PVC) specifies the desired access mode and storage capacity. Currently, based on only these two attributes, a PVC is bound to a single PV. Once a PV is bound to a PVC, that PV is essentially tied to the PVC’s project and cannot be bound to by another PVC. There is a one-to-one mapping of PVs and PVCs. However, multiple pods in the same project can use the same PVC.

PVC Object Definition
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: ceph-claim
spec:
  accessModes:     (1)
    - ReadWriteOnce
  resources:
    requests:
      storage: 2Gi (2)
1 As mentioned above for PVs, the accessModes do not enforce access right, but rather act as labels to match a PV to a PVC.
2 This claim will look for PVs offering 2Gi or greater capacity.
  1. Save the PVC definition to a file, for example ceph-claim.yaml, and create the PVC:

    # oc create -f ceph-claim.yaml
    persistentvolumeclaim "ceph-claim" created
    
    #and verify the PVC was created and bound to the expected PV:
    # oc get pvc
    NAME         STATUS    VOLUME                                     CAPACITY   ACCESSMODES   AGE
    ceph-claim   Bound     pvc-f548d663-3cac-11e7-9937-0024e8650c7a   2Gi        RWO           1m
                                     (1)
    1 the claim dynamically created a Ceph RBD PV.

Creating the Pod

A pod definition file or a template file can be used to define a pod. Below is a pod specification that creates a single container and mounts the Ceph RBD volume for read-write access:

Pod Object Definition
apiVersion: v1
kind: Pod
metadata:
  name: ceph-pod1           (1)
spec:
  containers:
  - name: ceph-busybox
    image: busybox          (2)
    command: ["sleep", "60000"]
    volumeMounts:
    - name: ceph-vol1       (3)
      mountPath: /usr/share/busybox (4)
      readOnly: false
  volumes:
  - name: ceph-vol1         (3)
    persistentVolumeClaim:
      claimName: ceph-claim (5)
1 The name of this pod as displayed by oc get pod.
2 The image run by this pod. In this case, we are telling busybox to sleep.
3 The name of the volume. This name must be the same in both the containers and volumes sections.
4 The mount path as seen in the container.
5 The PVC that is bound to the Ceph RBD cluster.
  1. Save the pod definition to a file, for example ceph-pod1.yaml, and create the pod:

    # oc create -f ceph-pod1.yaml
    pod "ceph-pod1" created
    
    #verify pod was created
    # oc get pod
    NAME        READY     STATUS    RESTARTS   AGE
    ceph-pod1   1/1       Running   0          2m
                          (1)
    1 After approximately a minute, the pod will be in the Running state.

Setting ceph-user-secret as Default for Projects

If you want to make the persistent storage available to every project, you must modify the default project template. Read more on modifying the default project template. Adding this to your default project template allows every user who has access to create a project access to the Ceph cluster.

Default Project Example
...
apiVersion: v1
kind: Template
metadata:
  creationTimestamp: null
  name: project-request
objects:
- apiVersion: v1
  kind: Project
  metadata:
    annotations:
      openshift.io/description: ${PROJECT_DESCRIPTION}
      openshift.io/display-name: ${PROJECT_DISPLAYNAME}
      openshift.io/requester: ${PROJECT_REQUESTING_USER}
    creationTimestamp: null
    name: ${PROJECT_NAME}
  spec: {}
  status: {}
- apiVersion: v1
  kind: Secret
  metadata:
    name: ceph-user-secret
  data:
    key: QVFCbEV4OVpmaGJtQ0JBQW55d2Z0NHZtcS96cE42SW1JVUQvekE9PQ== (1)
  type:
    kubernetes.io/rbd
...
1 Place the key from ceph-user-secret here in base64 format. See Creating the Ceph Secret.