---
- hosts: all

  pre_tasks:
    - name: Update apt cache.
      apt: update_cache=yes cache_valid_time=600
      when: ansible_os_family == 'Debian'

    - name: Override postfix_inet_protocols (RHEL).
      set_fact:
        postfix_inet_protocols: ipv4
      when: ansible_os_family == 'RedHat'

  roles:
    - role_under_test