Assume that i have an enterprise accounting application that consists of a front-end interface, a processing tier, and a back-end database. This is an application that contains private business data, and thus is traditionally run in a secure private network environment within the enterprise.

What are the challenges that appear when my enterprise desires to move the processing component of this application to a cloud computing data center in order to achieve greater scalability or to reduce IT costs ?

Pls note: do i have to make significant changes to my own infrastructure to enable external access to formerly private resources? do i have to modify the application code to handle new network topology ?

thanks, if you give your answers in a simple manner, really appreciated.