Ansible setting of hostname from inventory, but ignoring IP addresses

hosts.yml

- name: Ensure hostname set
  hostname:
    name: {{ inventory_hostname }}
  when: not inventory_hostname|trim is match('(\d{1,3}\.){3}\d{1,3}')

- name: Ensure hostname is in /etc/hosts
  lineinfile:
    dest: /etc/hosts
    regexp: "^{{ ansible_default_ipv4.address }}.+$"
    line: "{{ ansible_default_ipv4.address }} {{ ansible_fqdn }} {{ ansible_hostname }}"

---

• name: inventory name to hostname
  hostname:
  name: "{{ inventory_hostname }}"

Indeed @patsevanton — the original gist is in a really old format. You've correctly put the way things should be now 👍