That manifesto illustrates how you end up building your app if you launch it on Heroku. I've found the principles greatly increase my productivity no matter what platforms I'm using. One thing that did take me a little while to figure out: most of my apps are SSL-only, and I always want to interact with them over SSL in my development environment because odd things can creep up in production if you never test SSL locally. (Most of the advice that Rails blogs give always point you towards shutting off SSL in development mode which seems crazy to me)
At first I couldn't quite figure out how to make SSL work while complying with factor 7, Port Binding. I was still using Phusion Passenger with SSL configured as I described in this very old article (which still gets a lot of traffic).
Now here's what I do. I run the Pound reverse proxy using this configuration:
# http://lvh.me ListenHTTP Address 127.0.0.1 Port 80 Service BackEnd Address 127.0.0.1 Port 8080 End End End # https://lvh.me ListenHTTPS Address 127.0.0.1 Port 443 Cert "/usr/local/etc/pound.pem" AddHeader "X_FORWARDED_PROTO: https" Service BackEnd Address 127.0.0.1 Port 8080 End End End
/usr/local/etc/pound.pemfile is a locally-generated, locally-signed SSL certificate.
When I want to view an SSL-only app in my local browser, I just start Unicorn (my app container of choice) which defaults to port 8080. Then I visit https://lvh.me which is helpfully set to the loopback address 127.0.01. That hits Pound, which terminates the SSL connection (after a warning about the self-signed certificate), and proxies the web request to Unicorn.
This is very similar to what happens when the app runs in production on Heroku's systems, except that they use a Procfile in the root directory of the app to configure Unicorn. Per factor 7, it allows Heroku to bind my Unicorn instance to any arbitrary port:
web: bundle exec unicorn -p $PORT -c config/unicorn.rb