If you're running Rails in production it will by default be configured to let apache or nginx send files for you. If you're handling file downloads yourself with send_file

send_file("path/to/file.txt")

you will notice that the downloaded files are empty. To get around this just comment out the following in your config/environments/production.rb file.

  # comment out for production because apache/nginx are not doing this for us
  #config.action_dispatch.x_sendfile_header = "X-Sendfile"

Just finishing up brewing up some fresh ground comments...