I have a LAMP-based website/application and I'm preparing to start serving clients. With my current system, each client would need a full website instance (full folder structure from web-root up). I would like to separate out the core application while only creating the necessary customized files for each client.
Here's what I'm looking for: A way to say "if the file exists in the client folder, use that one. Otherwise, use the file from the core application folder." A sort of conditional or prioritized symlink, but working for a whole folder tree. That way I won't have to change code throughout the framework, and the separation can happen transparently to the application.
Does this functionality exist in Linux, or is it something I'd need to implement myself in the web server?