I use salt stack, and with all its warts I think it works just fine for environments with "pets". The idea is of course that in theory, you should be able to re-deploy any system as it's nothing but a collection of "states", but it works just as well for patching, maintaining and upgrading existing systems that never move.

I don't have much experience with Ansible or the other popular configuration management alternatives, but I don't imagine they are much different in this respect.