Generate /etc/hosts with Ansible

main.yml

# Idempotent way to build a /etc/hosts file with Ansible using your Ansible hosts inventory for a source.
# Will include all hosts the playbook is run on.
# Inspired from http://xmeblog.blogspot.com/2013/06/ansible-dynamicaly-update-etchosts.html

- name: "Build hosts file"
  lineinfile: dest=/etc/hosts regexp='.*{{ item }}$' line="{{ hostvars[item].ansible_default_ipv4.address }} {{item}}" state=present
  when: hostvars[item].ansible_default_ipv4.address is defined
  with_items: groups['all']