Apache load balancing with pound and rsync

To set this up I used two Ubuntu 12.04 web servers running Apache and a Raspberry Pi, running IPFire, as my load balancer using pound.

Configuring Apache

This document assumes that Apache is already configured on both hosts and serving your web site.

Configuring SSH login using private key authentication

On each host run

ssh-keygen

At the next prompt hit Enter. When it prompts for a password, leave them blank.

Check the contents of ‘~/.ssh’ and you should have id_rsa and id_rsa.pub

ls ~/.ssh

Now we need to put the contents of the id_rsa.pub file into authorized_keys on the remote computer. One each host you should execute the following command, replacing the ip address with your remote host.

ssh-copy-id -i ~/.ssh/id_rsa.pub username@ip_address

Enter the users password for that remote host when prompted. This should add the public key to that remote host in that users authrozed_keys file located in ~/.ssh/authorized_keys. You should now be able to ssh into the remote host without using a password.

ssh username@ip_address

NOTE: The permissions on the folder ~/.ssh should be 700, the authorized_keys file should be 600, id_rsa.pub should be 644, and id_rsa should be 600.

Configuring Rsync

To keep everything in sync I decided to use Rsync.

I create a bash script on each server to rsync the /var/www directory from the remote server. Then I used cron to run them every fifteen minutes. This is where the public key authentication comes in handy. This allows me to run remote commands without having to use a password.

My bash script was a simple rsync command that I saved to the file ~/sync_web.sh.

rsync -au -e ssh username@remote_host:/var/www/* /var/www/

I was able to use the same command on each host by just updating remote_host.

Setting up cron

The only thing left is to set the rsync command to run every fifteen minutes. First, edit crontab

crontab -e

At the end of the file add

*/15 * * * * ~/sync_web.sh

Configure pound

This section will be a bit different depending on what you use to run pound. In my case I loaded the software on my router, which is a Raspberry Pi running IPFire.

IPFire

To set up pound in IPFire I used this wiki article from the official IPFire wiki.

Start by installing the pound addon using pakfire.

Now /etc/sysconfig/pound with the following contents

run_pound=1  
pound_options=""  

Then create /etc/pound.cfg with the following contents

ListenHTTP  
Address 0.0.0.0  
Port    80  
Service  
    HeadRequire "Host: .*www.server0.com.*"  
    Session  
        Type    IP  
        TTL     3600  
    End  
    BackEnd  
      Address 192.168.0.10  
      Port    80  
    End  
    BackEnd  
        Address 192.168.0.11  
        Port    80  
    End  
  End  
End  

To finish the configuration off, enable External Access to port 80.

Ubuntu

Using Ubuntu you can install pound using the following command

sudo apt-get install pound

Edit /etc/default/pound
Change startup=0 to startup=1

Configure pound the same way as mentioned in the IPFire section above. The pound config can be found at /etc/pound/pound.cfg.

Now you can reboot, or start the pound daemon using

sudo /etc/init.d/pound start

All that is left is to forward port 80 to this host from the router.