# app/model/image.rb
def image_link(name_of_image)
 if File.exist? "/some/#{name_of_image}.jpg"
    path = "/some/#{name_of_image}.jpg"
 else
  external_image_link = external_api_call(name_of_image)
  DownloadImageWorker.perform_async(external_image_link) // perform it asynchronously
  external_image_link
 end

photo = Photo.find_or_initialize_by(external_url: image_url)
      img_responce = Faraday.get do |req|
        req.url image_url
        if photo.etag
          req.headers['If-None-Match'] = photo.etag
        end
      end

      case img_responce.status
      when 200
        # This mean, image changes (or new)
        photo.update external_url: image_url,
                     etag: img_responce.headers['etag'],
                     image: StringIO.new(img_responce.body)
      when 304
        # This mean, image doesn't change
      end