Multiple site architecture question

Hello,

I am in the planning stages of a RoR application. Eventually I will
need to multiple sites off of the single framework I’m going to build
out. Does anyone have experience running a similar architecture? How
would something like this be setup? Would you have one single /app
directory, and then various subdirectories in your /public folder for
each site:

/public/site1
/public/site2

I want to make sure I only need to update the codebase in one place
whenever I push a new feaure-set out…

Any pointers or whitepapers re: such an architecture?

Thanks!