PPA's are just Ubuntu's way to make creating APT repositories easier. Those steps above are the longer way of achieving the same result without relying on Canonical's infrastructure. The same instructions can also be used with minor changes to also work on Debian and Raspbian (and could probably work on most other Debian-based distros).

Those steps above are covering all the bases for Debian-based distros, adding the signing keys Docker uses for their packages, and then finally inst