gather host

# start with localhost as dummy target
- hosts: localhost
  gather_facts: no
  vars_prompt:
    - name: target_host
      prompt: "Ziel Host FQDN (target_host=<fqdn1>[,<fqdn2>]): "
      private: no
  tasks:
    - add_host:
        name: "{{ item }}"
        groups: target_host_group
      with_items: "{{ target_host.split(',') }}"
      tags:
        - debug

# now run playbook over target_host_group
- hosts: target_host_group
  vars_files: defaults.yml
  vars:
    ansible_ssh_pass: superawesomepwd     # default password for user, as there is no ssh-key yet
    ansible_user: user