Apache2 Cluster with Csync2 on Ubuntu 12.04 mini-HOWTO

For building a LAMP cluster, besides identity, filesystem and database synchronize, the next step would be service configure synchronize, e.g. Apache2 and PHP. This can be done by using Csync2, including configuration file status monitoring, synchronize and service restart.

This HOWTO will guide you though installation of Csync2 on Ubuntu 12.04. We will therefore handle both Apache2 and PHP5 for clustering with it.

Server Requirement

In this example let's assume we have 2 servers: dev6c1 and dev6c2, with domain name "localdomain" and IP information as below:

172.24.145.25 dev6c1.localdomain dev6c1
172.24.145.26 dev6c2.localdomain dev6c2

Where dev6c1 will be the master for Apache2 and PHP, where dev6c2 will be slave that clone dev6c1's configuration.

Install Csync2

This is simple for Ubuntu, just execute following command on both server:

aptitude -y install csync2

Creating Key File

At dev6c1, first generate the key file for secure connection:

openssl genrsa -out /etc/csync2_ssl_key.pem 1024
openssl req -new -key /etc/csync2_ssl_key.pem -out /etc/csync2_ssl_cert.csr
openssl x509 -req -days 600 -in /etc/csync2_ssl_cert.csr \
        -signkey /etc/csync2_ssl_key.pem -out /etc/csync2_ssl_cert.pem
csync2 -k /etc/csync2.key

Create Configuration File

Edit /etc/csync2.cfg and update as below:

group dev6 {
        host    dev6c1 (dev6c2);
        key     /etc/csync2.key;
        include /etc/apache2;
        include /etc/php5;
        action {
                pattern /etc/apache2/sites-enabled/*;
                pattern /etc/apache2/mods-enabled/*;
                pattern /etc/apache2/apache2.conf;
                pattern /etc/php5/*;
                exec    "/etc/init.d/apache2 restart";
                do-local;
        }
}

Initialize Csync2 Configuration by Synchronize Manually

Before real handy Csync2 cluster configuration synchronize start, we need to initialize Csync2 configuration manually with rsync as below at dev6c1:

rsync -av /etc/csync2* dev6c2:/etc/

Now restart daemon for both server:

/etc/init.d/openbsd-inetd restart

First Synchronize with Csync2 Manually

Before setup cron job for handling Csync2 periodically, let's trial manually at dev6c1:

csync2 -xv

If you get any error message you may try will following commands, too:

csync2 -xvvv
csync2 -TI

Else it should already works as expected.

Periodically Synchronize with Csync2

Now setup cron jobs with "crontab -e" as below:

*/1 * * * * csync2 -x >/dev/null 2>&1

Once save Csync2 will run once per 1 minute, check, synchronize and restart your service if required automatically.

Reference

• http://oss.linbit.com/csync2/
• http://oss.linbit.com/csync2/paper.pdf
• http://linuxaria.com/howto/csync2-a-filesystem-syncronization-tool-for-l...