[MBCook]

Is Elastic Beanstalk not an option? It doesn't replace hosts on redeploy so you wouldn't end up cycling through unnecessary instance.

[martin_]

Genuine question: Why is it okay to reuse instances because it's controlled via an abstraction layer, as opposed to doing it yourself?

[MBCook]

I agree, that doesn't make a difference.

I only mentioned EB because it does that kind of thing for you and if you don't have a highly complicated setup it makes rolling updates without changing instances very easy.