I checked most of the examples about Docker Swarm are building in the same physical machine running VirtualBox. So containers in different Docker-Machines can talk to each other no problem. My questions is if the containers are sitting in different Docker-Machines on different physical machines, it means that the Docker-Machines cannot talk to each other simply via the same VirtualBox bridge. So how we can make this work?
I think the whole purpose of Swarm is to let containers from different physical host can talk to each other.