---
- hosts: localhost
  remote_user: root
  become: yes
  become_method: sudo


  vars_prompt:

    - name: "root_password"
      prompt: "Enter your new root password"
      private: no
      when: root_password is not defined

  pre_tasks:

    - name: fail the play if the user missed out root_password
      fail: msg="root password should not be empty"
      when: root_password is not defined

  tasks:

    - name: Change root password
      user: name=root update_password=always password={{ root_password }}

when: root_password == ""