How to add var file in task level and not playbook level

[dudu.c (dudu.c...@gmail.com)]

This is not working

Thanks

- name: Update server etc/host 
  vars_files: /opt/defaults/defaults.yml
  lineinfile:
      path: /etc/hosts
      line: "{{ external_address }}    {{ service_name }}"
      state: present
      backup: yes