---
- name: Update default gateway
  hosts: all
  become: true
  vars:
    new_gateway: "192.168.1.254"

  tasks:
    - name: Replace gateway line in interfaces file
      lineinfile:
        path: /etc/network/interfaces
        regexp: '^(\s*)gateway\s+'
        line: "    gateway {{ new_gateway }}"
        backrefs: yes

    - name: Apply new default route immediately
      command: ip route replace default via {{ new_gateway }}