Static Asset Packaging for Rails 3 on Heroku

Short Version: the easiest way to combine and minify static assets (CSS and Javascript) in your Rails 3 app running on Heroku is to use AssetPackager with this fork of Heroku Asset Packager. It just works.

Long version: in his modern day classic, High Performance Web Sites, Steve Souders' very first rule is to “make fewer HTTP requests.” In practical terms, among other things, this means to combine separate CSS and Javascript files whenever possible. The creators of the Rails framework took this advice to heart, adding the :cache => true option to the javascript_include_tag and stylesheet_link_tag helpers to provide asset concatenation at no cost to the developer.

As time went on, our needs outgrew the capabilities of :cache => true and solutions like AssetPackager came onto the scene, offering increased control over how assets are combined as well as minification, stripping comments and unnecessary whitespace from CSS and Javascript files before packaging them together. Later, even more sophisticated solutions like Jammit arrived, offering even more minification capabilities including inlining small images into CSS.

Of course, static asset packaging wasn’t the only part of the Rails ecosystem that was undergoing major changes during this time. An increased emphasis on ease of deployment saw the rise of Capistrano, Passenger, and eventually Heroku, which offers hands-free system maintenance and simple git push heroku deployment. This simplification is not without trade-offs, though; you can only write to your app’s tmp directory and the lack of root access means that you can’t install additional software. Both of these limitations have ramifications for static asset packaging, namely:

  1. Both :cache => true and standard AssetPackager work by writing files into your app’s public directory, which, as you can likely guess, is verboten.

  2. Jammit has several compression options, but all of them require Java support, which we don’t have on Heroku. You have the option of compressing your assets and checking them into your repository by hand, but I for one can’t stand putting build artifacts in the repo.

I’ve seen a lot of questions about how to do static asset packaging on Heroku and just as many bad answers (which I’ll avoid linking to here). The best solution we’ve found uses AssetPackager along with this fork of Heroku Asset Packager that has been modified to work with Rails 3. It’s not the sexiest solution, but it works, and you’ll never have to think about it again.

David is Viget's managing development director. From our Durham, NC, office, he builds high-quality, forward-thinking software for PUMA, the World Wildlife Fund,, and many others.

More posts by David