Using Ceph RBD for dynamic provisioning - Persistent Storage Examples | Installation and Configuration

Overview
Creating a pool for dynamic volumes
Using an existing Ceph cluster for dynamic persistent storage
Setting ceph-user-secret as the default for projects

Overview

This topic provides a complete example of using an existing Ceph cluster for OpenShift Container Platform 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 Container Platform master host.
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.

Creating a pool for dynamic volumes

Install the latest ceph-common package:
```
yum install -y ceph-common
```
The ceph-common library must be installed on all schedulable OpenShift Container Platform nodes.

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:

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.

Create the Ceph secret for the client.admin:

$ oc create -f ceph-secret.yaml
secret "ceph-secret" created

Verify that the secret was created:

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

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.

Verify that the storage class was created:

$ oc get storageclasses
NAME                TYPE
dynamic (default)   kubernetes.io/rbd

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.

Create the PVC:

$ oc create -f ceph-pvc.yaml
persistentvolumeclaim "ceph-claim-dynamic" created

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

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.

Create the pod:

$ oc create -f ceph-pod1.yaml
pod "ceph-pod1" created

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.

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.