get device mounts info on kubernetes node using pod

Question

Team,

I have below pod.yaml that outputs the pod's mount info but now I want it to show me the node's mount info instead or also that info. any hint how can I give privilege to the pod such that it runs the same command on the k8s hosts on which the pod is running and list that in output of pods logs?

apiVersion: v1
kind: Pod
metadata:
  name: command-demo
  labels:
    purpose: demonstrate-command
spec:
  containers:
  - name: command-demo-container
    image: debian
    command: ["/bin/bash", "-c"]
    args:
      - |
        echo $HOSTNAME && mount | grep -Ec '/dev/sd.*\<csi' | awk '$0 <= 64  { print "Mounts are less than 64, that is found", $0 ;} $0 > 64  { print "Mounts are more than 64", $0 ;}'
  restartPolicy: OnFailure

kubectl logs pod/command-demo

command-demo
Mounts are less than 64, that is found 0

expected output:

k8s_node1 << this is hostname of the k8s node on which above pod us running
Mounts are more than 64, that is found 65

what change do i need to do in my pod.yaml such that it runs the shell command on node and not on pod?

Answer 1

You cannot access host filesystem inside the docker container unless you mount part's of the host filesystem as volume. You can try mounting the whole host filesytem into the pod as follows. You might need to privileged securityContext for the pod depending on what you are trying to do.

apiVersion: v1
kind: Pod
metadata:
 name: dummy
spec:
  containers:
    - name: busybox
      image: busybox
      command: ["/bin/sh"]
      args: ["-c", "sleep 3600"]
      volumeMounts:
        - name: host
          mountPath: /host
  volumes:
    - name: host
      hostPath:
        path: /
        type: Directory

Alternative method and probably better way is to SSH into the host machine from the pod and run the command. You can get the host IP using downward API - https://kubernetes.io/docs/tasks/inject-data-application/downward-api-volume-expose-pod-information/