Availability
Part of SEO is site availability, so recently we have installed NginX reverse proxies on the front of our apache webserver, this enables more simultaneous connections to be handled and helps to mitigate DDoS attacks by filtering requests to apache.
Our Active firewall cluster, allows one server being attacked to share the ip of its attacker with other machines in the cluster, so they can be “pro actively” protected.
Some tuning will be necessary, but the servers will be more secure.