How to mount volume with specific UID in Kubernetes Pod?

There is no way to set the UID using the definition of Pod, but Kubernetes saves the UID of sourced volume.

So, you can set the UID by InitContainer, which launches before the main container, just add it to the containers path of the Deployment:

initContainers:
- name: volume-mount-hack
  image: busybox
  command: ["sh", "-c", "chown -R 200:200 /nexus"]
  volumeMounts:
  - name: <your nexus volume>
    mountPath: /nexus

Like Anton said, although we can't set the UID using the definition of Pod. Here comes another workaround for this topic.

Please refer to the Kubernetes official document Configure a Security Context for a Pod or Container

The pod definition I used:

apiVersion: v1
kind: Pod
metadata:
  name: nexus3
  labels:
    app: nexus3
spec:
  securityContext:
    fsGroup: 200
  volumes:
  - name: nexus-data-vol
    emptyDir: {}
  containers:
  - name: nexus3-container
    image: sonatype/nexus3
    volumeMounts:
    - name: nexus-data-vol
      mountPath: /nexus-data

The Service definition:

apiVersion: v1
kind: Service
metadata:
  name: nexus3-service
spec:
  type: NodePort
  ports:
  - port: 8081
    nodePort: 30390
    protocol: TCP
    targetPort: 8081
  selector:
    app: nexus3

And then create pod and service without any permission denied or other errors:

# kubectl create -f nexus3.yaml
# kubectl create -f nexus3-svc.yaml

Try to login the Nexus3 container and check the owner/permission of /nexus-data:

# kubectl exec -it nexus3 -- sh
sh-4.2$ ls -ld /nexus-data/
drwxrwsrwx 16 root nexus 4096 Mar 13 09:00 /nexus-data/
sh-4.2$

As you can see, the directory belongs to root:nexus, and you can also check the files in the directory:

sh-4.2$ cd /nexus-data/
sh-4.2$ ls -l
total 72
drwxr-sr-x   3 nexus nexus  4096 Mar 13 09:00 blobs
drwxr-sr-x 269 nexus nexus 12288 Mar 13 08:59 cache
drwxr-sr-x   8 nexus nexus  4096 Mar 13 09:00 db
drwxr-sr-x   3 nexus nexus  4096 Mar 13 09:00 elasticsearch
drwxr-sr-x   3 nexus nexus  4096 Mar 13 08:59 etc
drwxr-sr-x   2 nexus nexus  4096 Mar 13 08:59 generated-bundles
drwxr-sr-x   2 nexus nexus  4096 Mar 13 08:59 instances
drwxr-sr-x   3 nexus nexus  4096 Mar 13 08:59 javaprefs
drwxr-sr-x   2 nexus nexus  4096 Mar 13 08:59 kar
drwxr-sr-x   3 nexus nexus  4096 Mar 13 08:59 keystores
-rw-r--r--   1 nexus nexus     8 Mar 13 08:59 lock
drwxr-sr-x   2 nexus nexus  4096 Mar 13 09:00 log
drwxr-sr-x   2 nexus nexus  4096 Mar 13 08:59 orient
-rw-r--r--   1 nexus nexus     5 Mar 13 08:59 port
drwxr-sr-x   2 nexus nexus  4096 Mar 13 08:59 restore-from-backup
drwxr-sr-x   7 nexus nexus  4096 Mar 13 09:00 tmp
sh-4.2$ touch test-file
sh-4.2$ ls -l test-file
-rw-r--r-- 1 nexus nexus 0 Mar 13 09:13 test-file
sh-4.2$ mkdir test-dir
sh-4.2$ ls -l test-dir
total 0
sh-4.2$ ls -ld test-dir
drwxr-sr-x 2 nexus nexus 4096 Mar 13 09:13 test-dir

That is the power of SetGID :)

Now Let's check the service is working or not. I use minikube to running a kubernetes cluster:

chris@XPS-13-9350 ~ $ minikube service nexus3-service --url
http://192.168.39.95:30390
chris@XPS-13-9350 ~ $ curl -u admin:admin123 http://192.168.39.95:30390/service/metrics/ping
pong

The service is working as expected.

How to mount volume with specific UID in Kubernetes Pod?

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