> Are they of necessity completely isolated units deployed with Docker and Kubernates on a CoreOS cluster and communicating only via HTTP each with independent databases?

I'm pretty sure the Docker, Kubernetes, and CoreOS parts are unnecessary (as, IIRC, microservices started being discussed before those tools were available -- those tools were driven in part by microservices, but aren't essential to the model.)

HTTP is, likewise, unnecessary: its the most obvious protocol choice, but there is no reason that microservices must be HTTP-based -- you could have a set of microservices using just about any protocol you want.