Rails Assets are AWOL in Production

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I’m working with Oddjob’s deployment workflow, and one of the first hurdles I ran into was that assets (CSS, JavaScript, images) weren’t found in production. I’m surprised that a framework who’s primary selling point is convention over configuration and just working out of the box, doesn’t just work out of the box in production.

After searching around, I discovered a simple fix for serving the CSS and JavaScript assets is to include the 12factor gem. I don’t know exactly what it does behind the scenes and I feel uneasy pulling more code (and implicit complexity) into the project to fix something that should never have been broken.

Fixing the images were a slightly different issue. I noticed that in production, Rails’ ‘Asset Pipeline’ adds cache-busters to all of the images, which is the right thing to do. It doesn’t use query strings — which was once The Right Way™ but is now known to be The Old Way™ — so it’s following best practice there too.

The problem is, all the image paths have to be rewritten in some compile step to match the new cache-busting filenames. Rails is not smart enough to recognise a relative asset path in a stylesheet and rewrite it. Instead, you have to change your native, portable style rules into a Rails-specific bastardisation.

// Normal style rule. Works everywhere.
  background: url(unicorn.png)

// Rails-specific. Also won’t work without quotes.
  background: asset_url('unicorn.png')

This is a minor pain practically, and a wisdom-tooth philosophically. It’s one example of Rails tightly coupling your otherwise agnostic code to the framework.