---
- name: reboot machine if required
  # 'all' is okay here, because the fail task will force the user to specify a limit on the command line, using -l or --limit
  hosts: 'all'

  tasks:
  - name: checking limit arg
    fail:
      msg: "you must use -l or --limit - when you really want to use all hosts, use -l 'all'"
    when: ansible_limit is not defined
    run_once: true
  
  - name: Check if reboot is required
    stat:
      path: /var/run/reboot-required
    register: reboot_required_file

  - name: Reboot if required
    become: true
    reboot:
    when: reboot_required_file.stat.exists == true