Comment 0 for bug 640065

See bug 380504 for historical context.

In short:
 - when we start to upgrade an appserver it may have requests live
 - haproxy will keep sending requests until the appserver falls over and dies

We need to change this to:
 - start the upgrade by telling the appserver to go out of rotation
 - that should close the listening port
 - we then check that that has happened (connect should error)
 - and then we bring up the new appserver
 - if the old appserver hasn't shut down after 200seconds (because of librarian proxied files)
   - kill it

ha proxy will stop forwarding requests cleanly once the listening socket is gone AIUI.