You can definitely do that. There is more programming involved, since you need to figure out how to tie a new instance deployment into Chef/Puppet/etc to update

You can definitely do that. There is more programming involved, since you need to figure out how to tie a new instance deployment into Chef/Puppet/etc to update HAProxy. You also need to figure out how to get it to update quickly. Finally, you'll need to figure out how to deploy your dual HAProxy server with heartbeat setup automatically every time you deploy a new type of microservice, and update DNS appropriately. It just means that instead of deploying Baker Street as part of your microservice push, you're deploying a) your microservice b) your dual HAProxy setup and/or new HAProxy config and c) DNS. Lots of ways to solve this problem; our big focus here is on simplicity. If you have the Chef-fu and time to do all the above, you could definitely make it work.