Use Drupal as a 'cloud system' frontend, what is your opinion?
You might want to look at Aegir.
It will let you manage multiple Drupal sites across multiple servers; you can add new servers via the Aegir master controller and once the servers are known to the controller you can create complex Drupal installs via the UI (Aegir master) with db on one server and code on other, mix and match, etc. 

One of the cool stuff is that Aegir can also take a drush make file and assemble a Drupal install for you; it supports Drupal distributions which let you not only install Drupal, but also Open Atrium, Pressflow, Open Publish, etc. 

If I were you I would definitely look at Aegir even if it doesn't take care of all my needs as it will be the only logical place to start extending. 

For an introduction see An introduction to the Aegir Hosting system. 

There are so many Aegir videos online; these are some of my favorites:


http://greenbeedigital.com.au/content/drupaldojo-introduction-aegir-hosting-system
By Miguel: http://greenbeedigital.com.au/content/installing-aegir-04-beta1
Again by Miguel; it's a must watch: http://greenbeedigital.com.au/content/building-drupal-applications-drushmake-provisioning-sites-aegir


If you like looking at code, here is the code for provisioning system which does all the magic: http://git.aegirproject.org/?p=provision.git;a=summary.