The experiment being run handles the machines. Those machines can be targets or attacker machines. Different types of machine controllers are covered by those plugins.
VM controller plugins can use SSH as a mixin class. This is implemented in *ssh_features.py* and reduces code duplication. In certain cases (for example if SSH needs some extra features) you can extend or replace methods from there. SSH handles:
Get the ip of the machine. If the machine is registered at the system resolver (/etc/hosts, dns, ...) a machine name would also be a valid response. As long as the network layer can reach it, everything is fine.