Well I had had them installed for sure. I have no idea what happened.

Does that mean it worked after re-installing them? The only thing I can think about is that you either changed the ruby version or the gemset. rvm manages gems per ruby version and per gemset. Seems you used ruby-2.2.1 with the gemset global. rvm list shows you any other installed rubys and once you select a given ruby (eg rvm use ruby-2.2.1) you can view the available gemsets via rvm gemset list. If you neither changed ruby version nor gemset, I really don't know.

Docker setup and adventurous... as if this rake setup hasn't been

LOL. To be fair, the problem is not so much in rake or Ruby per se. The problem is that so many Ruby gems use native extensions. In my experience most grief stems from compilation problems of native code. From an awestruct point of view it would be nice, if it just used pure Ruby dependencies. Unfortunately that's quite hard.

Regarding Docker - this setup has definitely its benefits. You skip worrying about the whole env setup part.