This is a weak article. The author's never worked with Docker before, so got tripped up by a few gotchas (but seriously, installing a third-party PPA isn't that hard or weird), but it doesn't take that much googling or trial/error to figure out how to do it right.

And the point of that is, once you know Docker, now installing just about any set of dependencies becomes a skill you know. I've never worked with Discourse. I've never worked with Rails. But because I've done Docker-based deployments, I bet I could indeed get it up and working in 30 minutes.