Friday, 11 October 2013

use HAProxy as HTTP load balancer

HAProxy can provide high availability, load balancing, and proxying for TCP and HTTP based application.

In my lab setup of HAProxy, I have 3 servers

centos-1, running apache
centos-2, running apache
centos, running HAProxy, HTTP requests to it will be forwarded to the other 2 servers

Here are my steps of setting up HAProxy to load balance between to HTTP servers.

1. on centos-1 and centos-2: install apache
# yum -y install httpd
create index.html for apache
# hostname -s > /var/www/html/index.html
disable iptables, start apache
# service iptables stop
# service httpd start

2. on centos, download HAProxy, the latest stable version is 1.4.24
# ./haproxy -v
HA-Proxy version 1.4.24 2013/06/17
Copyright 2000-2013 Willy Tarreau <>

3. edit haproxy configuration file, my sample haproxy.cfg, note this is for testing only, for complete configuration options, refer to
        maxconn 256

        mode http
        timeout connect 5000ms
        timeout client 50000ms
        timeout server 50000ms

frontend http-in
        bind *:80
        default_backend servers

backend servers
        balance roundrobin
        server server1 centos-1:80 maxconn 32
        server server2 centos-2:80 maxconn 32

4. start HAProxy
# ./haproxy -f haproxy.cfg

5. launch web browser, visit, you will see the page displaying "centos-1", this shows our request is being served by centos-1
refresh the page again, page will display "centos-2", our request is being served by centos-2 this time.

If we change balance roundrobin to balance source, our request will always being served by the same host, but using sticky session is still the preferred way to make sure clients always connect to the same backend server.

The setup is done, but it needs more tweaks before it can be used in production environment.things to check:
1. check backend server aliveness.
2. sticky session.
3. we need to change apache LogFormat on centos-1 centos-2 to reflect the real HTTP client address.

In our setup centos is the only server running HAProxy, it will be a single point of failure, we can setup centos cluster, and make HAProxy listening on the VIP.