andrewrk/connect-proxy — pull request #20 by Frozen2006 (2014-11-14 06:34:29+00:00)
Title: Bug with connection pool overflow was fixed

User's browser can terminate connection, but it wasn't handled in your code.
In this reasons, connection with remote server still being established even user's reponce stream is dead. (Users stream stops reading external server's stream, but still being piped with it). When count of 'Zomby' connections > 5 - proxy middleware stops processing requests.