The best documentation to…
The best documentation to date is the blog post above. The only option to push directly to a production site is the rsync approach. All the other methods are based on Git repositories assuming that once you commit with certain attributes (e.g. commit to master or with a tag) that the Git repository then triggers the deployment which can be done with Jenkins, Ansible, GitLab CI or any other automation tool in place.
What DRD auto-update does is to build the update of each site in a sandbox, verifying that everything is OK and nothing broke. Then it stores the result and the push to upstream will then happen with a tool that's your free choice. In can be inside DRD though, just write a plugin for that.
For further discussion on this, you may want to come over to Slack, Gitter or DrupalChat where an interactive communication is more efficient.
Jürgen Haas
Antwort auf DRD vs Aegir von Aaron (nicht überprüft)