ansible-roles/nameserver/tasks/main.yml

---
- name: Get actual nameserver
  shell: grep nameserver /etc/resolv.conf | awk '{ print $2 }'
  register: grep_nameserver
  check_mode: no
  changed_when: false
  tags:
  - nameserver

- name: Set nameserver
  lineinfile:
    dest: /etc/resolv.conf
    line: "nameserver {{ item }}"
    state: present
  loop: "{{ nameservers }}"
  tags:
  - nameserver

- name: Unset others nameserver
  lineinfile:
    dest: /etc/resolv.conf
    line: "nameserver {{ item }}"
    state: absent
  loop: "{{ grep_nameserver.stdout_lines }}"
  when: item not in nameservers
  tags:
  - nameserver