Hello, I published an article today on Yelp's engineering blog ( http://engineeringblog.yelp.com/2015/04/true-zero-downtime-haproxy-reloads.html) that shows a technique we use for low latency, zero downtime restarts of HAProxy. This solves the "when I restart HAProxy some of my clients get RSTs" problems that can occur. We built it to solve the RSTs in our internal load balancing, so there is a little more work to be done to modify the method to work with external traffic, which I talk about in the post.
The solution basically consists of using Linux queuing disciplines to delay SYN packets for the duration of the restart. It can definitely be improved by further tuning the qdiscs or replacing the iptables mangle with a u8/u32 tc filter, but I decided it was better to talk about the idea and if the community likes it, then we can optimize it further. -Joey
