carrierwave.rb

# config/initializers/carrierwave.rb
CarrierWave.configure do |config|
  if Rails.env.production?
    config.root      = Rails.root.join('tmp')
    config.cache_dir = 'carrierwave'
    config.storage   = :fog

    config.fog_credentials = {
      :provider               => 'AWS',
      :aws_access_key_id      => ENV['S3_KEY_ID'],
      :aws_secret_access_key  => ENV['S3_SECRET_KEY'],
      :persistent             => false # This is required to prevent write timeouts from PUT requests to S3
    }

    config.fog_directory  = ENV['S3_BUCKET']
    config.fog_host       = ENV['S3_HOST']
    config.fog_public     = true
    config.fog_attributes = {'Cache-Control'=>'max-age=315576000'} # Cache for 1 year
  else
    config.storage = :file
  end
end