# yum install ceph-common
OKD clusters can be provisioned with persistent storage using Ceph RBD.
Persistent volumes (PVs) and persistent volume claims (PVCs) can share volumes across a single project. While the Ceph RBD-specific information contained in a PV definition could also be defined directly in a pod definition, doing so does not create the volume as a distinct cluster resource, making the volume more susceptible to conflicts.
This topic presumes some familiarity with OKD and Ceph RBD. See the Persistent Storage concept topic for details on the OKD persistent volume (PV) framework in general.
Project and namespace are used interchangeably throughout this document. See Projects and Users for details on the relationship.
High-availability of storage in the infrastructure is left to the underlying storage provider.
To provision Ceph volumes, the following are required:
An existing storage device in your underlying infrastructure.
The Ceph key to be used in an OKD secret object.
The Ceph image name.
The file system type on top of the block storage (e.g., ext4).
ceph-common installed on each schedulable OKD node in your cluster:
# yum install ceph-common
Define the authorization key in a secret configuration, which is then converted to base64 for use by OKD.
In order to use Ceph storage to back a persistent volume, the secret must be created in the same project as the PVC and pod. The secret cannot simply be in the default project.
ceph auth get-key on a Ceph MON node to display the key value for the
apiVersion: v1 kind: Secret metadata: name: ceph-secret data: key: QVFBOFF2SlZheUJQRVJBQWgvS2cwT1laQUhPQno3akZwekxxdGc9PQ== type: kubernetes.io/rbd
Save the secret definition to a file, for example ceph-secret.yaml, then create the secret:
$ oc create -f ceph-secret.yaml
Verify that the secret was created:
# oc get secret ceph-secret NAME TYPE DATA AGE ceph-secret kubernetes.io/rbd 1 23d
Developers request Ceph RBD storage by referencing either a PVC, or the Gluster
volume plug-in directly in the
volumes section of a pod specification. A PVC
exists only in the user’s namespace and can be referenced only by pods within
that same namespace. Any attempt to access a PV from a different namespace
causes the pod to fail.
Define the PV in an object definition before creating it in OKD:
apiVersion: v1 kind: PersistentVolume metadata: name: ceph-pv (1) spec: capacity: storage: 2Gi (2) accessModes: - ReadWriteOnce (3) rbd: (4) monitors: (5) - 192.168.122.133:6789 pool: rbd image: ceph-image user: admin secretRef: name: ceph-secret (6) fsType: ext4 (7) readOnly: false persistentVolumeReclaimPolicy: Retain
|1||The name of the PV that is referenced in pod definitions or displayed in
|2||The amount of storage allocated to this volume.|
|4||The volume type being used, in this case the rbd plug-in.|
|5||An array of Ceph monitor IP addresses and ports.|
|6||The Ceph secret used to create a secure connection from OKD to the Ceph server.|
|7||The file system type mounted on the Ceph RBD block device.|
Changing the value of the
Save your definition to a file, for example ceph-pv.yaml, and create the PV:
# oc create -f ceph-pv.yaml
Verify that the persistent volume was created:
# oc get pv NAME LABELS CAPACITY ACCESSMODES STATUS CLAIM REASON AGE ceph-pv <none> 2147483648 RWO Available 2s
Create a PVC that will bind to the new PV:
kind: PersistentVolumeClaim apiVersion: v1 metadata: name: ceph-claim spec: accessModes: (1) - ReadWriteOnce resources: requests: storage: 2Gi (2)
|2||This claim looks for PVs offering
Save the definition to a file, for example ceph-claim.yaml, and create the PVC:
# oc create -f ceph-claim.yaml
See the full Volume Security topic before implementing Ceph RBD volumes.
A significant difference between shared volumes (NFS and GlusterFS) and block
volumes (Ceph RBD, iSCSI, and most cloud storage), is that the user and group
IDs defined in the pod definition or container image are applied to the target
physical storage. This is referred to as managing ownership of the block device.
For example, if the Ceph RBD mount has its owner set to 123 and its group ID
set to 567, and if the pod defines its
runAsUser set to 222 and its
fsGroup to be 7777, then the Ceph RBD physical mount’s ownership will be
changed to 222:7777.
Even if the user and group IDs are not defined in the pod specification, the resulting pod may have defaults defined for these IDs based on its matching SCC, or its project. See the full Volume Security topic which covers storage aspects of SCCs and defaults in greater detail.
A pod defines the group ownership of a Ceph RBD volume using the
stanza under the pod’s
spec: containers: - name: ... securityContext: (1) fsGroup: 7777 (2)
|2||All containers in the pod will have the same fsGroup ID.|