As other posters have mentioned the solution in this link is actually suboptimal. I showed how the iptables solution leads to 1-3s latency for connections that establish during the restart but you can avoid it by getting a little more hardcore.

See http://engineeringblog.yelp.com/2015/04/true-zero-downtime-h... or http://inside.unbounce.com/product-dev/haproxy-reloads/ for solutions that are even better than this one.