Although many of the pieces of the Ansible Core Engine are plugins that can be swapped out via playbook directives or configuration, there are still pieces of the Engine that are not modular. The documents here give insight into how those pieces work together.
See also
© 2012–2016 Michael DeHaan
© 2016 Red Hat, Inc.
Licensed under the GNU General Public License version 3.
https://docs.ansible.com/ansible/dev_guide/developing_core.html