carrierwave setup

carrierwave.rb

# sample config/initializers/carrierwave.rb
CarrierWave.configure do |config|
	if Rails.env.development? || Rails.env.test?
    config.storage = :file
  else
  	config.storage = :fog
	  config.fog_credentials = {
	    provider: "AWS",
	    aws_access_key_id: ENV["AWS_ACCESS_KEY_ID"],
	    aws_secret_access_key: ENV["AWS_SECRET_ACCESS_KEY"]
	  }
	  config.fog_directory = ENV["AWS_S3_BUCKET"]
	end
end

setup.md

gem 'carrierwave'
gem "fog", "~> 1.3.1"

rails generate uploader Avatar

this should give you a file in:

app/uploaders/avatar_uploader.rb

comment the default storage

class AvatarUploader < CarrierWave::Uploader::Base
  #storage :file
end