Kubernetes: how to set VolumeMount user group and

Question

I'm running a Kubernetes cluster on AWS using kops. I've mounted an EBS volume onto a container and it is visible from my application but it's read only because my application does not run as root. How can I mount a PersistentVolumeClaim as a user other than root? The VolumeMount does not seem to have any options to control the user, group or file permissions of the mounted path.

Here is my Deployment yaml file:

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: notebook-1
spec:
  replicas: 1
  template:
    metadata:
      labels:
        app: notebook-1
    spec:
      volumes:
      - name: notebook-1
        persistentVolumeClaim:
          claimName: notebook-1
      containers:
      - name: notebook-1
        image: jupyter/base-notebook
        ports:
        - containerPort: 8888
        volumeMounts:
        - mountPath: "/home/jovyan/work"
          name: notebook-1

Answer 1

I ended up with an initContainer with the same volumeMount as the main container to set proper permissions, in my case, for a custom Grafana image.

initContainers:
- name: take-data-dir-ownership
  image: alpine:3.6
  # Give `grafana` user (id 472) permissions a mounted volume
  # https://github.com/grafana/grafana-docker/blob/master/Dockerfile
  command:
  - chown
  - -R  
  - 472:472
  - /var/lib/grafana
  volumeMounts:
  - name: data
    mountPath: /var/lib/grafana

• https://kubernetes.io/docs/concepts/workloads/pods/init-containers/

This is necessary when the main image in a pod is running as a user other than root and needs write permissions on a mounted volume.

Answer 2

The Pod Security Context supports setting an fsGroup, which allows you to set the group ID that owns the volume, and thus who can write to it. The example in the docs:

apiVersion: v1
kind: Pod
metadata:
  name: hello-world
spec:
  containers:
  # specification of the pod's containers
  # ...
  securityContext:
    fsGroup: 1234

More info on this is here

Answer 3

This came as one of the challenges for the Kubernetes Deployments/StatefulSets, when you have to run process inside a container as non-root user. But, when you mount a volume to a pod, it always gets mounted with the permission of root:root.

So, the non-root user must have access to the folder where it wants to read and write data.

Please follow the below steps for the same.

1. Create user group and assign group ID in Dockerfile.
2. Create user with user ID and add to the group in Dockerfile.
3. change ownership recursively for the folders the user process wants to read/write.

4. Add the below lines in Deployment/StatefulSet in pod spec context.

   spec:
     securityContext:
       runAsUser: 1099
       runAsGroup: 1099
       fsGroup: 1099
   

runAsUser

Specifies that for any Containers in the Pod, all processes run with user ID 1099.

runAsGroup

Specifies the primary group ID of 1099 for all processes within any containers of the Pod.

If this field is omitted, the primary group ID of the containers will be root(0).

Any files created will also be owned by user 1099 and group 1099 when runAsGroup is specified.

fsGroup

Specifies the owner of any volume attached will be owner by group ID 1099.

Any files created under it will be having permission of nonrootgroup:nonrootgroup.

Answer 4

For k8s version 1.10+, runAsGroup has been added, it's similar to fsGroup but works differently.

Implementation can be tracked here: https://github.com/kubernetes/features/issues/213

Answer 5

To change the file system permission run the initcontainer before actual container start

here example for elastic search pod

initContainers:
      - command:
        - sh
        - -c
        - chown -R 1000:1000 /usr/share/elasticsearch/data
        - sysctl -w vm.max_map_count=262144
        - chgrp 1000 /usr/share/elasticsearch/data
        image: busybox:1.29.2
        imagePullPolicy: IfNotPresent
        name: set-dir-owner
        resources: {}
        securityContext:
          privileged: true
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File
        volumeMounts:                         #Volume mount path
        - mountPath: /usr/share/elasticsearch/data
          name: elasticsearch-data

To change user group in container

spec:
      containers:
      securityContext:
          privileged: true
          runAsUser: 1000