I didn't mean to imply that NodeJS isn't the best fit for the problem at hand. I was just trying to clarify that it doesn't take an asynchronous framework like Node to keep processing a request after the connection is closed.
Yeah, even with a simple Perl CGI, all you have to do is close STDOUT if you want the HTTP response to end, but continue processing the request.
Of course, it's trivial to write request methods that bypass the rack middleware in Rails.