looks great from a quick scroll through… good job 
feedback:
- I would strongly suggest using a package manager like asdf (or other) to install elixir and even node (to be able to maintain dev/staging/prod parity by installing very specific versions - and also to have elixir compiled against the used otp version)
- Making nginx optional - eg showing how to run phoenix directly on port 80, would be a nice addition. + ssl maybe?
also check out @ziazek 's A Beginner's Guide To Deployment with Edeliver and Distillery - that has articles on automated DB backup - and ssl setup… (maybe check if @ziazek has any good steps to perform that you might have missed…)
