Configure mount options for pods that are backed by PersistentVolumes (NFS or other volume types) in OpenShift 4?

Solution Verified - Updated

Environment

  • Red Hat OpenShift Container Platform (RHOCP)
    • 4
  • Persistent Volumes Mount Options

Issue

  • Is it possible to configure mount options for volumes in OpenShift 4?
  • How to configure NFS mount options for pods backed by NFS PV?
  • When creating a pod backed by NFS Persistent Volume, default mount options are set. How to edit these NFS mount options?

Resolution

It is not possible to configure required mount options (for NFS or other volume types) directly in the pods, but they can be specified while creating a PersistentVolume by using the PV attribute spec.mountOptions, or using the mountOptions field from StorageClasses for dynamically provisioned PVs.
>Note: currently, Red Hat does not ship a NFS CSI Driver that supports dynamic provisioning of NFS volumes. .

Refer to the Diagnostic Steps section for examples for manually creating PersistentVolumes backed by NFS with customized mount options (like nfsvers and soft).

Root Cause

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It is possible to configure mount options (for NFS or other volume types) directly in the PersistentVolumes via the spec.mountOptions field, or in the mountOptions field from StorageClasses for dynamically provisioned PersistentVolumes.
>Note: currently, dynamic provisioning NFS volumes is not supported in OpenShift 4.

Refer to the upstream Kubernetes documentation about the PersistentVolumes types supporting Content from kubernetes.io is not included.mount options, and to the StorageClasses Content from kubernetes.io is not included.mount options.

Diagnostic Steps

  • Check the description of the PersistentVolume spec.mountOptions:

    $ oc explain persistentvolume.spec.mountOptions
KIND:     PersistentVolume
VERSION:  v1

FIELD:    mountOptions <[]string>

DESCRIPTION:
     mountOptions is the list of mount options, e.g. ["ro", "soft"]. Not
     validated - mount will simply fail if one is invalid. More info:

  • Check the description of the StorageClass mountOptions:

    $ oc explain storageclass.mountOptions
GROUP:      storage.k8s.io
KIND:       StorageClass
VERSION:    v1

FIELD: mountOptions <[]string>

DESCRIPTION:
    mountOptions controls the mountOptions for dynamically provisioned
    PersistentVolumes of this storage class. e.g. ["ro", "soft"]. Not validated
    - mount of the PVs will simply fail if one is invalid.

  • Example creating persistent volume with customized mountOptions:

    apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs-pv001
spec:
  capacity:
    storage: 5Gi
  accessModes:
  - ReadWriteMany
  mountOptions:
  - nfsvers=4.1
  - soft
  persistentVolumeReclaimPolicy: Retain
  nfs:
    path: /nfs
    server: bastion.srocp4.example.com

  • Create persistent volume claim with generated NFS volume: 

    apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: nfs-claim
spec:
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 5Gi
  volumeName: nfs-pv001
  storageClassName: ""

  • Create a pod backed by NFS volume :

    kind: Pod
apiVersion: v1
metadata:
  name: nfspod
spec:
  containers:
    - name: app
      image: ubi9
      volumeMounts:
      - name: nfs-volume
        mountPath: /mnt/nfs
      command: ["/bin/sh"]
      args: ["-c", "sleep 500000"]
  volumes:
    - name: nfs-volume
      persistentVolumeClaim:
        claimName: nfs-claim

    $ oc get pods
NAME           READY   STATUS    RESTARTS   AGE
nfs-in-a-pod   1/1     Running   0          78m
nfspod         1/1     Running   0          4m38s  <----

  • Verify if customized mountOptions are applied properly:

    $ oc rsh pod/nfspod 
/ # mount |grep nfs
bastion.srocp4.example.com:/nfs on /mnt/nfs type nfs4 (rw,relatime,vers=4.1,rsize=524288,wsize=524288,namlen=255,soft,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=10.74.252.218,local_lock=none,addr=10.74.250.148)

    $ oc debug node/[node_name]
[...]
sh-5.1# chroot /host bash
[root@node_name /]# mount | grep -i nfs
bastion.srocp4.example.com:/nfs on /var/lib/kubelet/pods/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/volumes/kubernetes.io~nfs/nfs-volume type nfs4 (rw,relatime,vers=4.2,rsize=524288,wsize=524288,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=10.74.252.218,local_lock=none,addr=10.74.250.148)
bastion.srocp4.example.com:/nfs on /var/lib/kubelet/pods/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/volumes/kubernetes.io~nfs/nfs-pv001 type nfs4 (rw,relatime,vers=4.1,rsize=524288,wsize=524288,namlen=255,soft,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=10.74.252.218,local_lock=none,addr=10.74.250.148)                          # <---- mounted with soft, 4.1 that is specified when creating nfs pv.
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