Overview

This topic provides a complete example of using an existing Ceph cluster for OpenShift Origin persistent storage. 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.

  • Run all oc commands on the OpenShift Origin master host.

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

Creating a pool for dynamic volumes

  1. Install the latest ceph-common package:

    yum install -y ceph-common

    The ceph-common library must be installed on all schedulable OpenShift Origin nodes.

  2. From an administrator or MON node, create a new pool for dynamic volumes, for example:

    $ 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

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

Using an existing Ceph cluster for dynamic persistent storage

To use an existing Ceph cluster for dynamic persistent storage:

  1. Generate the client.admin base64-encoded key:

    $ ceph auth get client.admin
    Ceph secret definition example
    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 value is required for Ceph RBD to work with dynamic provisioning.
  2. Create the Ceph secret for the client.admin:

    $ 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
  4. Create the storage class:

    $ oc create -f ceph-storageclass.yaml
    storageclass "dynamic" created
    Ceph storage class example
    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 A comma-delimited list of IP addresses Ceph monitors. This value is required.
    2 The Ceph client ID that is capable of creating images in the pool. The default is admin.
    3 The secret name for adminId. This value is required. The secret that you provide must have kubernetes.io/rbd.
    4 The namespace for adminSecret. The default is default.
    5 The Ceph RBD pool. The default is rbd, but this value is not recommended.
    6 The Ceph client ID used to map the Ceph RBD image. The default is the same as the secret name for adminId.
    7 The name of the Ceph secret for userId to map the Ceph RBD image. It must exist in the same namespace as the PVCs. Unless you set the Ceph secret as the default in new projects, you must provide this parameter value.
  5. Verify that the storage class was created:

    $ oc get storageclasses
    NAME                TYPE
    dynamic (default)   kubernetes.io/rbd
  6. Create the PVC object definition:

    PVC object definition example
    kind: PersistentVolumeClaim
    apiVersion: v1
    metadata:
      name: ceph-claim-dynamic
    spec:
      accessModes:  (1)
        - ReadWriteOnce
      resources:
        requests:
          storage: 2Gi (2)
    1 The accessModes do not enforce access rights but instead act as labels to match a PV to a PVC.
    2 This claim looks for PVs that offer 2Gi or greater capacity.
  7. Create the PVC:

    $ oc create -f ceph-pvc.yaml
    persistentvolumeclaim "ceph-claim-dynamic" created
  8. Verify that 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
  9. Create the pod object definition:

    Pod object definition example
    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
        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, busybox is set 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 in the container.
    5 The PVC that is bound to the Ceph RBD cluster.
  10. Create the pod:

    $ oc create -f ceph-pod1.yaml
    pod "ceph-pod1" created
  11. Verify that the pod was created:

    $ oc get pod
    NAME        READY     STATUS   RESTARTS   AGE
    ceph-pod1   1/1       Running  0          2m

After a minute or so, the pod status changes to Running.

Setting ceph-user-secret as the default for projects

To make persistent storage available to every project, you must modify 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. See modifying the default project template for more information.

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 your Ceph user key here in base64 format.