ensure that the current `hostname` is defined in `/etc/hosts`

main.yml

---
# Because not everything is correct in this world, we may end up with a host that doesn't have the reported
# hostname in the hosts file.

    - name: ensure that the current host is in /etc/hosts. Yes this is a thing.
      sudo: true
      replace:
        backup: yes
        dest: /etc/hosts
        regexp: '^(127\.0\.1\.1(?!.*\b{{ ansible_hostname }}\b).*)$'
        replace: '\1 {{ ansible_hostname }}'