While deploying a load balancer, we need some mechanism to inform loadbalancer to forward request to different set of servers based on the condition specified. Here I’m using HAProxy load balancer on CentOS 5 box. This is a very small test setup in Amazon EC2 environment having 3 small instances.

Let’s start the action. Login to server where you want to install HAProxy. Download it and extract it. You can download source and compile but as its a single executable file, I prefer to download precompiled file for being lazy

$ mkdir /usr/local/haproxy
$ cd /usr/local/haproxy
$ wget http://haproxy.1wt.eu/download/1.3/bin/haproxy-1.3.15.2-pcre-40kses-splice-linux-i586.notstripped.gz
$ gunzip haproxy-1.3.15.2-pcre-40kses-splice-linux-i586.notstripped.gz
$ mv haproxy-1.3.15.2-pcre-40kses-splice-linux-i586.notstripped haproxy
$ chmod 700 haproxy

As an example, we have two backend servers/domains, one to serve static contents and other for dynamic contents. Let’s create config file:

$ vi haproxy.cfg
 
  defaults
    balance roundrobin
    cookie SERVERID insert indirect</code>
 
  frontend www 10.252.130.162:80
    mode http
    acl dyn_content url_sub cgi-bin
    use_backend dyn_server if dyn_content
    default_backend stat_server
 
  backend dyn_server
    mode http
    server dserver1 dynamic.example.com:80 cookie A check
 
backend stat_server
    mode http
    server sserver1 static.example.com:80 cookie B check</code>

Here, 10.252.130.162 is the IP of your load balancer server. HAProxy configuration file has several sections called defaults, listen, frontend and backend. We used cookie to forward all subsequent requests from same user to same backend. The main thing here is the acl in frontend section which stats that if there’s a word “cgi-bin” in user’s url then use dyn_server as backend otherwise use default backend which is stat_server. You should refer HAProxy documentation for further information of configurations.

Save the file and check it for syntax:

$ ./haproxy -f ./haproxy.cfg -c

It will throw warnings regarding missing timeouts in sections, you can ignore these warnings. If there’s any error, check the config file again.

Run HAProxy:

$ ./haproxy3 -f ./haproxy.cfg -p /var/run/haproxy.pid

Put load balancer’s public IP/domain name in your browser and test this setup, it should go as expected.

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