heroku assets not found 404

Question

We are dealing with an issue where our assets are compiling w/o any issues during slug compilation. However, starting yesterday after a push to both our staging and production applications, we are now running into issues where the browser is indicating that the assets can't load for some reason.

Using the browser dev tools we are seeing this error: Failed to load resource: the server responded with a status of 404 (Not Found) : /assets/application-a3b17e738ce8996d058795310e3cd9b4.js

The first thing we decided to do was rollback our codebase to the last commit (which was the commit that was fully functional in a previous heroku push). The same issue exists where the browser can't load the asset.

Using bash, I connected to the heroku instance and checked out the public/assets directory to ensure the assets were actually there. They are ALL there with the correct hash codes preceding the file names. The files are not empty and the manifest file looks good to go. I'm not sure what else to try at this point. We've never had issues until now with loading of assets. There is nothing in the heroku push logs that indicate anything is throwing an error at any point.

Answer 1

I had the same issue. It seems to be fixed for me after including the rails_12factor gem in my production gems (in my Gemfile). I found this out after reading the first part of this Heroku Support page: https://devcenter.heroku.com/articles/rails4

Logging and assets

Heroku treats logs as streams and requires your logs to be sent to STDOUT. To enable STDOUT logging in Rails 4 you can add the rails_12factor gem. This gem will also configure your app to serve assets in production. To add this gem add this to your Gemfile:

gem 'rails_12factor', group: :production

This gem allows you to bring your application closer to being a 12factor application. You can get more information about how the gem configures logging and assets read the rails_12factor README. If this gem is not present in your application, you will receive a warning while deploying, and your assets and logs will not be functional.

The 'rails_12factor' gem has gem dependencies on the rails_serve_static_assets gem and rails_stdout_logging. Basically, if you don't want your Rails app using its precious cycles on processing requests just to serve assets then you'll need to figure out a different solution such as a CDN: https://devcenter.heroku.com/articles/using-amazon-cloudfront-cdn-with-rails