The problem with the CoreOS tools is that they're pretty tightly coupled. We looked into using fleet to manage our deployments. Unfortunately, it relies on a minor feature of etcd and cannot work with Consul, our corporate standard. Flannel? Yep, again, tightly coupled with etcd.

I like some of the ideas behind the CoreOS tools, but until they start playing well with others, they're a non-starter for me. I'm not interested in tools that try to lock me into other, inferior, tools.