Drupal VM uses the Ansible provisioner to build all the software that runs and supplements Drupal sites.
The Ansible configuration uses a variety of open source community-maintained Ansible Roles that are hosted on Ansible Galaxy, but Drupal VM includes the roles in the codebase for efficiency's sake.
You should NOT make any manual changes to the roles in the roles directory, but rather, contribute to the upstream roles corresponding to the role's folder name (e.g. for issues with the geerlingguy.apache role, see the geerlingguy.apache role page on Ansible Galaxy, and the role's issue tracker on GitHub).
From time to time, third party roles need to be added or updated to enable new Drupal VM functionality or fix bugs. To update a role (e.g. geerlingguy.apache), find the role's version setting inside requirements.yml, bump the version to the required or latest version of the role, then run the following command in the same directory as this README file:
$ ansible-galaxy install -r requirements.yml --force
Then commit the updated requirements.yml file and the new and updated files within the roles directory in a new PR to the Drupal VM project.