Ubuntu – what is the default ha-proxy load balance algorithm

The TCP RTO (receive timeout) starts at three seconds. (RFC 1122) If a transmitted packet hasn't had an acknowledgement returned in that time, then it's assumed to be lost and retransmitted. This is almost certainly what the author is referring to. (Note that the RTO gets tuned up or down dynamically by various algorithms, outside the scope of this question.)

Keep in mind that this really only applies to connections between your frontend server and the clients (i.e. web users). In normal scenarios, the connections between HAProxy and your backend servers should be on a LAN and you should use much shorter timeouts, so that malfunctioning backends get taken out of service sooner.

As for your web users, some of them may be on very high latency connections, such as satellite, and may experience higher than normal retransmits due to this. The RTT on a connection where a satellite is in use may exceed 2000 ms even if all is well.

With all this in mind, you will generally want very short timeouts for timeout connect and very long ones for timeout client.

For timeout server, this depends on your web application. When setting the timeout, consider the complexity of the web app being served, and how long it might take in the worst case to process a complex request. If in doubt, raise the value.

There are a few ways to go about this. Many providers will allow you to rent or buy a load balancing device like a F5 or something like that. These devices can load balance tcp connections and many level 7 connections to a set of machines. Now if you are unable to get a load balanacer on hardware there are other choices out there like nginx, haproxy, and apache all have load balancing tools to do this.

I recommend that you go with a hardware one if you can you have a project that needs something to be super fast. Dont get me wrong I use a lot of nginx proxying. Some times I have tcp proxy to ha proxy for level 7. Since the hardware load balancers wont need to use as much power and you can use a lot more nginx loads to handle the rest of the traffic, this is useful when you need to do a lot of SSL termantions, to get hardware load balancers to do a lot of ssl cost a lot but apache,haproxy,nginx can do it for fairly cheap.

Nginx: http://wiki.nginx.org/HttpProxyModule https://github.com/yaoweibin/nginx_tcp_proxy_module

Apache: https://httpd.apache.org/docs/2.2/mod/mod_proxy_balancer.html

HaProxy: http://tenfourty.com/2011/04/09/how-to-load-balance-tcp-connections-with-haproxy/