Legacy application migration strategy - advice required on strategy

Question

I'm currently working on moving a complex classic ASP website (v1) over to a new ASP.NET MVC 3 version (v2). The database is going to be retained and used for v2. As I build v2, the business continues to modify and add features to v1. All of the features of v1 are required along with some fairly complex functional improvements in v2.

Because of the continuing work on v1, I'm currently thinking the best strategy for this is to produce v2 with the same functionality (although with stronger framework, better practices etc) as v1, release to the point where the applications could be ran in parallel, and then add new features once this is stable.

Where database schema changes are occurring on the v1, I'm concerned about trying to do too much for the first iteration of v2.

Does anyone have any insight on this type of project and advise on whether this is a good approach?

Answer 1

As long as you're using the same database, I'd look for ways to segment the application, upgrading one segment at a time. Try to minimize the windows where v2 "goes dark" with respect to v1, as this increases risk. There just aren't too many ways to keep v2 in sync with live changes to v1 -- even if you've got good unit test coverage for v2, you won't have that in v1 (I assume), so your ability to compare apples-to-apples is pretty small, IMO.