Load balancing helps provide redundancy to your website. However, one often asked question is how to keep your content synchronized on each server. If you put a new web page on one server, how does it get copied over to the second server? In this article, i’ll explain how to use rsync command to synchronize data between a specific directory on each server.

Install rsync

On Centos Linux type the following command:

yum install rsync

Using rsync command with password authentication

For example, i have two servers using for load balanced and called server1(192.168.1.101) and server2(192.168.1.102). I wanted to keep data in /var/www/html sync between to servers. Type the following command on server1:

rsync -avr --progress --links --rsh='/usr/bin/ssh' 192.168.1.102:/var/www/html /var/www/html

With:
-avr : archive mode (a), verbose (v), recurse into directories (r).
–progress: Show progress.
–links: copy symlinks as symlinks.
–rsh: use to specify the remote shell ssh to use.
192.168.1.102:/var/www/html: IP address of server2 and path to synchronize to server1
/var/www/html: Server1 path

Using rsync command with SSH certificate

Replace above command with following command:

rsync -avr --progress --links --rsh='/usr/bin/ssh -i /path_to_private_key' 192.168.1.102:/var/www/html /var/www/html

A sample shell script

#!/bin/bash
SOURCEPATH='source'
DESTPATH='destination'
SOURCEHOST='ip_address'
PRIVATEKEY='private_key'
LOGFILE='log_file'
SSH='/usr/bin/ssh'
rsync -avr --progress --links --rsh="'$SSH -i $PRIVATEKEY'" $SOURCEHOST:$SOURCEPATH $DESTPATH 2>&1 >> $LOGFILE

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