I use PaaS provider AppFog.com. They allow containerization of sites, so that each domain & subdomain can be easily separated from another. This is very important to me, as it allows me to assign contractors to each container without fear of them interfering with whoever is working on another container.
For example, I may have a main company site: http://www.example.com on one IP address, a store store.example.com on another IP address, and a control panel manage.example.com on a third container. This would allow me to delegate each app to a different person without fear of them stepping on each others’ toes.
That said, I would need a way to link these frontward facing PHP-containers, and that would be through a shared database. This would allow multiple sites to share the same users, for instance.
I have read about multi-site manager, and I understand that it is intended for PHP-sites on the same host. This may not work for my situation, as I am looking for multiple separate hosts each on unique IP addresses to share the users/sessions.
Thoughts, please?
edit: this Wordpress solution sounds similar: http://justintadlock.com/archives/2008/09/20/installing-two-wordpress-blogs-with-the-same-users
That utilitzes CUSTOM_USER_TABLE and CUSTOM_USER_META_TABLE.