I upgraded a new app to use Rails 4.2 and bootstrap and I thought things were fine. However, when I went to the page today, css wasn’t working. It just never created the css files. Turns out that I needed to add the ‘sprockets-rails’ gem to my Gemfile because the asset pipeline is no longer a feature of rails 4. Once I ran bundle and commit this change to the repo, I could deploy and things worked fine.