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Mounting Volumes on Privileged Pods

Overview

Persistent volumes can be mounted to pods with the privileged security context constraint (SCC) attached.

While this topic uses GlusterFS as a sample use-case for mounting volumes onto privileged pods, it can be adapted to use any supported storage plug-in.

Prerequisites

Creating the Persistent Volume

Creating the PersistentVolume makes the storage accessible to users, regardless of projects.

  1. As the admin, create the service, endpoint object, and persistent volume:

    $ oc create -f gluster-endpoints-service.yaml
$ oc create -f gluster-endpoints.yaml
$ oc create -f gluster-pv.yaml

  2. Verify that the objects were created:

    $ oc get svc
NAME              CLUSTER_IP      EXTERNAL_IP   PORT(S)   SELECTOR   AGE
gluster-cluster   172.30.151.58   <none>        1/TCP     <none>     24s
    $ oc get ep
NAME              ENDPOINTS                           AGE
gluster-cluster   192.168.59.102:1,192.168.59.103:1   2m
    $ oc get pv
NAME                     LABELS    CAPACITY   ACCESSMODES   STATUS      CLAIM     REASON    AGE
gluster-default-volume   <none>    2Gi        RWX           Available                       2d

Creating a Regular User

Adding a regular user to the privileged SCC (or to a group given access to the SCC) allows them to run privileged pods:

  1. As the admin, add a user to the SCC:

    $ oc adm policy add-scc-to-user privileged <username>

  2. Log in as the regular user:

    $ oc login -u <username> -p <password>

  3. Then, create a new project:

    $ oc new-project <project_name>

Creating the Persistent Volume Claim

  1. As a regular user, create the PersistentVolumeClaim to access the volume:

    $ oc create -f gluster-pvc.yaml -n <project_name>

  2. Define your pod to access the claim:

    Example 1. Pod Definition
    apiVersion: v1
id: gluster-S3-pvc
kind: Pod
metadata:
  name: gluster-nginx-priv
spec:
  containers:
    - name: gluster-nginx-priv
      image: fedora/nginx
      volumeMounts:
        - mountPath: /mnt/gluster (1)
          name: gluster-volume-claim
      securityContext:
        privileged: true
  volumes:
    - name: gluster-volume-claim
      persistentVolumeClaim:
        claimName: gluster-claim (2)
    1 Volume mount within the pod.
    2 The gluster-claim must reflect the name of the PersistentVolume.

  3. Upon pod creation, the mount directory is created and the volume is attached to that mount point.

    As regular user, create a pod from the definition:

    $ oc create -f gluster-S3-pod.yaml

  4. Verify that the pod created successfully:

    $ oc get pods
NAME                 READY     STATUS    RESTARTS   AGE
gluster-S3-pod   1/1       Running   0          36m

    It can take several minutes for the pod to create.

Verifying the Setup

Checking the Pod SCC

  1. Export the pod configuration:

    $ oc get -o yaml --export pod <pod_name>

  2. Examine the output. Check that openshift.io/scc has the value of privileged:

    Example 2. Export Snippet
    metadata:
  annotations:
    openshift.io/scc: privileged

Verifying the Mount

  1. Access the pod and check that the volume is mounted:

    $ oc rsh <pod_name>
[root@gluster-S3-pvc /]# mount

  2. Examine the output for the Gluster volume:

    Example 3. Volume Mount
    192.168.59.102:gv0 on /mnt/gluster type fuse.gluster (rw,relatime,user_id=0,group_id=0,default_permissions,allow_other,max_read=131072)