I’m describing here the steps I followed to download, install and configure it in Ubuntu Server. We have 2 backend Web servers which will receive traffic from Load balancer host running HAProxy in front of them.

Step 1. Download, compile and install HAproxy from here :

$ cd /usr/src
$ wget http://haproxy.1wt.eu/download/1.4/src/haproxy-1.4.11.tar.gz
$ tar xzf haproxy-1.4.11.tar.gz 
$ cd haproxy-1.4.11
$ make install

You can find an example of config file in /usr/src/haproxy-1.4.11/examples/haproxy.cfg which you copy in /etc/haproxy and update it per your requirement.

Step 2. Update config file per your requirements:

$ mkdir /etc/haproxy
$ cp /usr/src/haproxy-1.4.11/examples/haproxy.cfg /etc/haproxy
$ cd /etc/haproxy

you can see configs I used for our server below:

$ cat haproxy.cfg
global
        log 127.0.0.1  local0
        log 127.0.0.1  local1 notice
        log loghost    local0 info
        maxconn 4096
        uid 99
        gid 99
        daemon
        #debug
        #quiet
 
defaults
        log    global
        mode    http
        option httplog
        option dontlognull
        retries 3
        option redispatch
        maxconn 2000
        contimeout      5000
        clitimeout      50000
        srvtimeout      50000
 
listen  web-service 0.0.0.0:80
        option forwardfor
        option httpchk OPTIONS /health_check.html
        stats enable
        stats refresh 10s
        stats hide-version
        stats scope   .
        stats uri     /lb?stats
        stats realm   LB2\ Statistics
        stats auth    admin:Adm1nn
 
        server  web1 10.x.x.x:80 check inter 2000 fall 3
        server  web2 10.x.x.x:80 check inter 2000 fall 3

Most important section in this config file is “listen” where we have several important options. Few are related to display stats and in the end there are entries of backend web server which actually serves the traffic.

I’ve used most of default options and update it little bit to accommodate my requirements. There’s lots of optimization needed and therefore this can be called as a bare configuration. I would write about further enhancements later after some more experiments.

Because backend web servers receive traffic from Load balancer so in usual case they will see IP address of Load balancer itself instead of real user, I’ve written a post earlier to fix this.

You can also use HAProxy to do content switching where it will divert traffic amoung several backend servers available based on specified conditions, I’ve written a detailed post on this topic earlier.

Step 3. Start the daemon:
After initial config, you can start daemon and check things. Let’s check syntax first:

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

If no issues in config, let’s start he process:

$ haproxy -f haproxy.cfg

HAProxy is started, you can quickly check its status page at http://your-lb-ip/lb?status where you need to supply user and password as per we specified in config file.

You can keep updating your config file and reload the haproxy service without having to stop/start it:

$ haproxy -f haproxy -p /var/run/haproxy.pid -st $(cat /var/run/haproxy.pid)

In its default config, HAProxy send logs to a syslog facility: local0, via a socket connection. By default, your syslog configuration probably doesn’t accept socket connections, and even doesn’t have a local0 facility, so you have no HAProxy log. If you want it, configure syslog to accept TCP connections by adding -r to syslogd parameters.

On a RedHat/CentOS server, edit the value of SYSLOGD_OPTIONS in /etc/sysconfig/syslog:

SYSLOGD_OPTIONS="-m 0 -r"

On a Debian/Ubuntu server, edit the value of SYSLOGD in /etc/default/syslogd:

SYSLOGD="-r"

Then set up syslog facility local0 and direct it to file /var/log/haproxy.log or your desired location by editing /etc/syslog.conf:

local0.* /var/log/haproxy.log

finally, restart syslog service to apply changes:

$ /etc/init.d/syslog restart

You can see that HAProxy logging is started.

Other useful article on this blog that you may like to read:
* Configure HAProxy for content switching
* 5 Steps to secure your Production Linux Server
* Ensuring secure access to your Production Linux Server
* Bash script to backup essential log files in Linux Server

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.

You may also like to read:
* 5 steps to secure your Linux Server
* Ensuring secure access to production Linux Servers
* Bash script to backup essential log files in Linux
* Quickly change your ssh port from defualt 22 to something higher
* SSH port forwarding from remote to local machine
* Save root or user history to check later
* Install and configure denyhost to prevent brute force attacks

Step 1. Download perlbal OR install it via perl cpan, like this:

$ perl -MCPAN -e shell
cpan-> install perlbal

Step 2. Find out its sample config (/root/.cpan/build/Perlbal-1.60/doc/config-guide.txt) or if you downloaded and compiled it, file will be there. Put this file in /etc/perlbal as perlbal.conf.

$ mkdir /etc/perlbal
$ cp /root/.cpan/build/Perlbal-1.60/doc/config-guide.txt /etc/perlbal/perlbal.conf

Step 3. Update the perlbal.conf file as per your requirements.
for example, we are using it as load balancer, here is sample config

$ vi /etc/perlbal/perlbal.conf
CREATE POOL my_apaches
SET nodefile = conf/nodelist.dat  # IP of backend Apache servers.
 
CREATE SERVICE balancer
SET listen          = 0.0.0.0:80
SET role            = reverse_proxy
SET pool            = my_apaches
SET persist_client  = on
SET persist_backend = on
SET verify_backend  = on
ENABLE balancer
 
# Keep an internal management port open to reconfigure pool automatically via telnet
CREATE SERVICE mgmt
SET role   = management
SET listen = 127.0.0.1:60000
ENABLE mgmt

Step 4. Start perlbal module as daemon.

$ perlbal -d

Step 5. Test by connecting through management port

$ telnel 127.0.0.1 60000

Step 6. One major concern is that the backend servers will log entries with IP address of load balancer instead of actual user’s IP. To overcome this issue, install and configure mod_rpaf for apache at backend servers. Login in backend server and install the module:

$ cd /usr/src/
$ wget http://stderr.net/apache/rpaf/download/mod_rpaf-0.6.tar.gz
$ tar xzf mod_rpaf-0.6.tar.gz
$ cd mod_rpaf-0.6
$ apxs -i -c -n mod_rpaf-2.0.so mod_rpaf-2.0.c
$ vi /etc/httpd/conf/httpd.conf
LoadModule rpaf_module modules/mod_rpaf-2.0.so
RPAFenable On
RPAFsethostname On
RPAFproxy_ips 127.0.0.1 192.168.0.1  ## replace your IP of load balancer
RPAFheader X-Forwarded-For
 
$ service httpd restart

Testing

Step 1. Create a simple perl file and put it in cgi-bin directory of all backend servers.

$ vi /var/www/cgi-bin/test.pl
#!/usr/bin/perl
print "Content-Type: text/html\n\n";
print " Web server load balance testing ";
print "Web Server running fine.";
 
# Fetch IP of server
my $ifout =`ifconfig eth0 | grep inet`;
$ifout =~ m/\s+inet\saddr:([\d\.]+)\s.+/g;
 
print "This page is fetched from: $1 Server.";

Step 2. Start testing from browser and try to access the perl script from your load balancer server. Add more backends (by updating perlbal.conf) and test again. As per the load you will notice that perl script will be fetched from different back ends.

Adding / removing backends on the fly

Step 1. To maximum utilize the load balanced environment, there should be some technique by which backend servers can be added or removed on fly in the pool of perlbal as per the load. The topic of measuring load of backend servers and then making right decision is beyond the scope of this post. I developed some perl scripts to achieve the same in Amazon EC2[aws.amazon.com/ec2] environment, where we can create/remove servers on fly. If you are also on EC2, just post a comment or send mail to me and I will happily give scripts to you. Updating perlbal using a perl script with the help of Net::Telnet module is very easy. Here’s sample code:

use Net::Telnet;
$telnet=new Net::Telnet(Host=>$loadbalancerIP,Port=>60000,Timeout=>20, Errmode=>'Die');
$telnet->print("pool my_apaches add $newserverIP");
$telnet->waitfor('/OK/i');
$telnet->close;

Its Done. Play with it. One of the noticed minus point (as of ver 1.60), perlbal is not so efficient/capable while handling https connections. In case you have website which doesnt require https connections, perlbal should be given preferrence.

An alternate to perlbal is haproxy load balancer, I’ve covered it here, here and here as well.

You may also like to read:

* Install and configure haproxy load balancer, lightweight and fast alternative of perlbal/apache proxy.
* Enable or fix logging for Haproxy or perlbal load balancer.
* Install and setup haproxy load balancer for content switching.
* 5 steps to secure your Linux Server
* Ensuring secure access to production Linux Servers
* Bash script to backup essential log files in Linux