general app dev question

I am working on an app in PHP that requires users to have their own separate subdomains, much like a Blinksale or Backpackit, and I am struggling with the best way to maintain a single code base across all the domains. Obviously I want to make any front-end, back-end or database changes once and have them propogate down to all the subdomains. I have a few ideas on how to do this but being a relative noob in the large app dev world I'd be curious what other DH users have done or even had ideas about. I'm very concerned about performance as well as scalability from a dev perspective.

Thanks,
Steve

Take a queue from Frameworks. Look into CakePHP if you're not sure how they work. It requires a single PHP file within the document root (index.php) and everything else can be stored in a separate location.

How do you plan to maintain the subdomains? At this time, DH does not allow automated creation of subdomains.

Subdomains will be created manually for reasons even beyond what DH allows. I'll look into Cake - call in the files using require definitely crossed my mind but I was a little concerned about performance if a lot of users are calling the same file using a require or include function.

In reply to:
I was a little concerned about performance if a lot of users are calling the same file using a require or include function.

*nix systems allow any number of people to look at the same file, no problem. It's no different than bunch of people looking at their own copy.