Setup carrierwave in Rails with just fog-aws.

application.rb

# inside application.rb...
class Application < Rails::Application

  # TODO Stop-gap workaround to carrierwave doing "require 'fog'"
  # This let's us get ./lib in the load path, where our own
  # fog.rb is loaded for carrierwave, but we've already loaded
  # fog-aws, which is all we need anyway.
  config.before_configuration do
    require 'carrierwave'
  end

  # ... the rest of your config ...
end

carrierwave.rb

# config/initializers/carrierwave.rb
require 'fog/aws'

CarrierWave.configure do |config|
  # ... your usual configuration ...
end

fog.rb

# lib/fog.rb
module Fog
  # This file only exists so carrierwave has
  # something to require.
end

Gemfile

# your Gemfile should look something like...
gem 'fog-aws', require: false # or require: 'fog/aws'

# avoid having carrierwave loading during bundler
# setup.  We need to get ./lib in the load_path first.
gem 'carrierwave', require: false

Update: Newer versions of carrierwave have support to set the fog_provider in the config.
Therefore its now enough to add

config.fog_provider = 'fog/aws'

to your carrierwave config as described in the carrierwave readme

@gugl The docs don't mention that

@jasonfine You're right, thanks for pointing that out. It seems that fog_provider was deprecated in carrierwave 2.0.0 according to https://github.com/carrierwaveuploader/carrierwave/blob/f81bb4d90c610c4e5d68c2057ab977620d7089a1/CHANGELOG.md#deprecated

"...just adding fog providers to Gemfile will load them" in carrierwave >= 2.0

Current solution in readme: https://github.com/carrierwaveuploader/carrierwave#using-amazon-s3