Persistent Volume Claim for Azure Disk with specific user permissions

Question

I'm trying to create a dynamic Azure Disk volume to use in a pod that has specific permissions requirements.

The container runs under the user id 472, so I need to find a way to mount the volume with rw permissions for (at least) that user.

With the following StorageClass defined

apiVersion: storage.k8s.io/v1
kind: StorageClass
provisioner: kubernetes.io/azure-disk
reclaimPolicy: Delete
volumeBindingMode: Immediate
metadata:
  name: foo-storage
mountOptions:
  - rw
parameters:
  cachingmode: None
  kind: Managed
  storageaccounttype: Standard_LRS

and this PVC

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: foo-storage
  namespace: foo
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: foo-storage
  resources:
    requests:
      storage: 1Gi

I can run the following in a pod:

containers:
  - image: ubuntu
    name: foo
    imagePullPolicy: IfNotPresent
    command:
      - ls
      - -l
      - /var/lib/foo
    volumeMounts:
      - name: foo-persistent-storage
        mountPath: /var/lib/foo
volumes:
  - name: foo-persistent-storage
    persistentVolumeClaim:
      claimName: foo-storage

The pod will mount and start correctly, but kubectl logs <the-pod> will show

total 24
drwxr-xr-x 3 root root  4096 Nov 23 11:42 .
drwxr-xr-x 1 root root  4096 Nov 13 12:32 ..
drwx------ 2 root root 16384 Nov 23 11:42 lost+found

i.e. the current directory is mounted as owned by root and read-only for all other users.

I've tried adding a mountOptions section to the StorageClass, but whatever I try (uid=472, user=472 etc) I get mount errors on startup, e.g.

mounting arguments: --description=Kubernetes transient mount for /var/lib/kubelet/plugins/kubernetes.io/azure-disk/mounts/m1019941199 --scope -- mount -t ext4 -o group=472,rw,user=472,defaults /dev/disk/azure/scsi1/lun0 /var/lib/kubelet/plugins/kubernetes.io/azure-disk/mounts/m1019941199
Output: Running scope as unit run-r7165038756bf43e49db934e8968cca8b.scope.
mount: wrong fs type, bad option, bad superblock on /dev/sdc,
       missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.

I've also tried to get some info from man mount, but I haven't found anything that worked.

How can I configure this storage class, persistent volume claim and volume mount so that the non-root user running the container process gets access to write (and create subdirectories) in the mounted path?

GKE throws a similar error when I add - uid=2000 - gid=3000. "wrong fs type, bad option, bad superblock on /dev/sdb, missing codepage or helper program, or other error." — yuranos

Utku Özdemir Utku Özdemir · Accepted Answer · 2018-11-25T02:30:20

You need to define the securityContext of your pod spec like the following, so it matches the new running user and group id:

securityContext:
  runAsUser: 472
  fsGroup: 472

The stable Grafana Helm Chart also does it in the same way. See securityContext under Configuration here: https://github.com/helm/charts/tree/master/stable/grafana#configuration

Persistent Volume Claim for Azure Disk with specific user permissions

1 Answers