multi server configuration

Our site (fighthunger.org) is currently running on 3 web servers (LAMP - apache2, mysql5, php5). We faced some issue and I would like to submit our solution and asking for suggestion.

Server configuration

We use Subversion SVN to manage our php code. In repository we skip files/ directory; we don't need versioning those file and they are weigh down repository itself. Repository reside on one of three server (fh_1)
On each server we svncheckedout repository to a working copy (says /var/www/vh/fighthunger), so we have 3 copy of the same code on each server.
Directory files/ is NFSshared between 3 servers

Code base replication

After each commit (from a local working copy on local testing server) we configure post-commit script to synch all 3 working copy in different servers. It a little tricky because post-commit run without environment as apache user (the user running web server) and need to connect to 3 other servers. This is done by copying rsa apache public key on 3 server and run a command like

ssh "cd /var/www/vhostsbalanced/fh; svn update"

In this way change propagate almost instantly.

Drupal issue

Drupal seems not to have any problem running in this environment (session are stored in database). Only problem could arise from files/ directory but we solve using a NFS share.

Hope this could help.