For testing ansible roles, I need a docker container that runs systemd or init - a container in which services can be enabled. I also need this container to be accessible via ssh. This way, I don't have to spin up cloud resources (which are not free) in order to test doing something on a remote.

Molecule is a testing framework designed for Ansible roles, collections, and playbooks. In the Ansible ecosystem, it provides a structured workflow to develop and verify infrastructure as code. 

This is an example of setting up a NAT inside docker - in a fairly self-explanatory and minimal way. There are three examples that you can run in this setup: a positive example, a negative example, and a chatty positive example for debugging and demonstration purposes.

I have two versions: one for linux, and one for mac. If anyone knows how to combine them into one, please post in comments below!