Elastic Load Balancing is part of Amazon’s EC2 service. While I have not tried it, I have always wanted to implement it on our setup some time in the future.
If your website relies on PHP sessions, it is important to keep the site visitor on the same server and not getting load balanced to another server while the visitor is still on the website. The following should work:
elb-create-app-cookie-stickiness-policy myLoadBalancer --cookie-name PHPSESSID --policy-name followPHPPolicy elb-set-lb-policies-of-listener myLoadBalancer --lb-port 80 --policy-names followPHPPolicy
This will create a policy on the ELB to follow the PHP session timeout specified by the PHPSESSID.