Upgrading application - how to keep the DNS name?

I usually setup a new virtual server, called foo-new or foo-mig (migration) for example, and have a pilot group of users test the app using the new name. Once the new app is "proven" ready for prime time, I add the new server(s) to the pool serving foo.company.com, and disable the old server(s) in the pool. Then if for any reason you need to revert to the old app, simply disable the new servers, enable the old... After some period of time that you feel really comfortable with the new servers, simply remove the old servers from the pool.

 

 

If you really want to have one virtual server served by two pools, you could get creative with an irule and define a pool of addresses representing the group of users that you want to send to the new pool, then have the irule choose a pool of servers based on what pool of addresses they came from, but if you are new to using F5's that's probably more risk than its worth....