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CSI driver FsGroup User Guide

Attention: This user guide to apply fsgroup to volumes provisioned by filestore driver is applicable for stable-master overlay driver manifest bundle, deployed to kubernetes 1.19+ clusters. For 1.19 (CSIVolumeFSGroupPolicy feature gate needs to be manually enabled). For a workaround to apply fsgroup on clusters 1.19 (with CSIVolumeFSGroupPolicy feature gate disabled), and clusters <= 1.18 see user-guide here

Attention: CSIVolumeFSGroupPolicy is a Kubernetes feature which is Beta is 1.20+, Alpha(1.19).

Attention: CSIDriver object fsGroupPolicy field is added in Kubernetes 1.19 (alpha) and cannot be set when using an older Kubernetes release. For 1.20+ k8s versions the feature is be enabled by default.

Kubernetes uses fsGroup to change permissions and ownership of the volume to match user requested fsGroup in the pod's SecurityContext. Kubernetes feature CSIVolumeFSGroupPolicy is a beta feature in K8s 1.20+ by which CSI drivers can explicitly declare support for fsgroup. Read more about CSIVolumeFSGroupPolicy here and here.

FsGroup example

  1. Create StorageClass

    If you haven't created a StorageClass yet, create one first:

    $ kubectl apply -f ./examples/kubernetes/fsgroup/demo-sc.yaml

    If a non-default network is used for the filestore instance, provide a network paramter to the storage class.

    apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
name: csi-filestore
provisioner: filestore.csi.storage.gke.io
parameters:
  network: <network name> # Change this network as per the deployment
volumeBindingMode: WaitForFirstConsumer
allowVolumeExpansion: true

  2. Check the CSI driver object for the filestore driver. It should report fsGroupPolicy: File

    $ kubectl get csidriver filestore.csi.storage.gke.io -o json
{
    "apiVersion": "storage.k8s.io/v1",
    "kind": "CSIDriver",
    ...
    "spec": {
        "attachRequired": false,
        "fsGroupPolicy": "File",
        "podInfoOnMount": true,
        "volumeLifecycleModes": [
            "Persistent"
        ]
    }
}

  3. Create Pod with fsgroup and using a PVC with ReadWriteMany access mode, provisioned by CSI Filestore driver.

    $ kubectl apply -f ./examples/kubernetes/fsgroup/pod-with-fsgroup.yaml

  4. Verify that the pod is up and running and fsgroup ownerhsip change is applied in the volume.

$ kubectl exec busybox-pod -- ls -l /tmp
total 16
drwxrws---    2 root     4000         16384 Jan 27 04:27 lost+found