rails – application.css asset not found in production mode

Rails by default doesn’t serve assets under public. See your production.rb:

  config.serve_static_assets = true

Change that to true and you’re good to go. (Note: you don’t want that to be true in production, remember to change it back before deploying!)

See Configuring Rails Applications for details.

In rails 6, in the default production.rb there should be a line

config.public_file_server.enabled = ENV['RAILS_SERVE_STATIC_FILES'].present?

So run your server with

RAILS_SERVE_STATIC_FILES=true rails server -e production

or set config.public_file_server.enabled=true in production.rb. See answers below for rails 4 and 5.