Kubelet Kubeconfig File Permissions Set To 600 Or More Restrictive

#!/usr/bin/env bash
#
# Harden kubelet.conf permissions on all worker nodes.
# Usage:
#   1) Create an inventory file with one worker node (IP or hostname) per line, e.g.:
#        /etc/kubernetes/worker-nodes.txt
#   2) Run:
#        bash secure-kubelet-kubeconfig.sh /etc/kubernetes/worker-nodes.txt
#
# Requirements:
#   - Run from any machine with SSH access to every worker node.
#   - SSH key-based auth to each node as a user with sudo privileges.
#   - 'stat', 'chmod', and 'sudo' available on the worker nodes.

set -euo pipefail

INVENTORY_FILE="${1:-}"

if [[ -z "${INVENTORY_FILE}" || ! -f "${INVENTORY_FILE}" ]]; then
  echo "Usage: $0 /path/to/worker-nodes.txt" >&2
  exit 1
fi

SSH_USER="${SSH_USER:-$(whoami)}"
SSH_OPTS="${SSH_OPTS:--o BatchMode=yes -o StrictHostKeyChecking=accept-new}"

REMOTE_FILE="/etc/kubernetes/kubelet.conf"
TARGET_PERMS="600"

echo "Using SSH user: ${SSH_USER}"
echo "Worker node inventory: ${INVENTORY_FILE}"
echo "Target permissions for ${REMOTE_FILE}: ${TARGET_PERMS}"
echo

while IFS= read -r NODE || [[ -n "$NODE" ]]; do
  # Skip empty lines and comments
  [[ -z "$NODE" || "$NODE" =~ ^# ]] && continue

  echo "==== Processing worker node: ${NODE} ===="

  # Check if file exists
  if ! ssh ${SSH_OPTS} "${SSH_USER}@${NODE}" "test -e '${REMOTE_FILE}'"; then
    echo "  [SKIP] ${REMOTE_FILE} not found on ${NODE}"
    continue
  fi

  # Ensure permissions are 600 (idempotent: running chmod 600 repeatedly is safe)
  ssh ${SSH_OPTS} "${SSH_USER}@${NODE}" "sudo chmod ${TARGET_PERMS} '${REMOTE_FILE}'"

  # Verification (adapted from audit command)
  PERMS=$(ssh ${SSH_OPTS} "${SSH_USER}@${NODE}" "/bin/sh -c 'if test -e \"${REMOTE_FILE}\"; then stat -c permissions=%a \"${REMOTE_FILE}\"; fi'")

  if [[ "${PERMS}" == "permissions=${TARGET_PERMS}" ]]; then
    echo "  [OK] ${REMOTE_FILE} permissions on ${NODE} are ${PERMS}"
  else
    echo "  [WARN] ${REMOTE_FILE} permissions on ${NODE} are ${PERMS}, expected permissions=${TARGET_PERMS}" >&2
  fi

  echo
done < "${INVENTORY_FILE}"

echo "Completed kubelet.conf permission hardening on all listed worker nodes."