config/initializers/carrierwave.rb

CarrierWave.configure do |config|
  # For testing, upload files to local `tmp` folder.
  config.storage = :file
  config.cache_dir = "#{Rails.root}/tmp/uploads" # To let CarrierWave work on heroku

  if Rails.env.test?
    config.enable_processing = false
    config.root = "#{Rails.root}/tmp"
  elsif Rails.env.production?
    if ENV['S3_KEY'].present?
      config.fog_credentials = {
          provider: 'AWS',
          aws_access_key_id: ENV['S3_KEY'],
          aws_secret_access_key: ENV['S3_SECRET'],
          region: ENV['S3_REGION']
      }
      config.storage = :fog
      config.fog_directory = ENV['S3_BUCKET_NAME']
    end
  end
end