In a previous article, we discussed Docker Machine, a tool to create Docker hosts in the cloud. Docker Machine can be extremely handy for local testing if you are on Windows and OS X, but it also adds another dimension when you use it to start Docker hosts in your favorite cloud provider and/or create a cluster.
We then used Machine to go straight into an advanced subject and create a Docker Swarm, which is a cluster of Docker hosts. A cluster of Docker hosts is needed to run a truly distributed application in production. In this article, we will look at setting up networking for a Swarm to allow containers to communicate with each other across hosts. Indeed, a Swarm cluster allows us to use the native single host networking of Docker, but it also allows us to create a network overlay backed by VXLAN. Containers started in this overlay can communicate out of the box with each other. This article will show you how to create, use, and test an overlay network using Docker Swarm.