My goal is to have 1 centralized place for the Application + DB and all the domains will serve pages from that place (without copying all the files)
My goal is to eliminate the need to copy my app to 5 different domains, and everythime there is a new feature an update 5 is needed on 5 different places.
I checked this: accessing files across domains that are hosted on the same server, but it didnt help.
as long as the domains are on the same physical server this can be accomplished.
Your code will reside outside the web root:
your index.php in each of the domains should look something like this:
you will be able to set instance specific variables in the index.php for each domain.
HTH