Docker released its production-ready multi-host overlay networking functionality in Docker 1.9. Before this release, the functionality was classed as experimental.
An overlay network is a computer network that is built on top of another network. Nodes in the overlay network can be thought of as being connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network:
In Docker terms, it allows containers on one Docker host to talk directly to containers on another Docker host as if they were on the same host, as shown in the following screenshot:
As you can see from the preceding diagram, there ...