To see Docker Swarm in action, we'll simulate an Ubuntu cluster. We'll bring up the
cd node that we'll use for orchestration, one node that will act as Swarm master and two nodes that will form the cluster. Up to this point, we always used Ubuntu 14.04 LTS (long term support) since it is considered stable and supported for a long time. The next long term support version will be 15.04 LTS (not released at the time this book was written). Since some of the features we'll explore later on, throughout this chapter, will need a relatively new Kernel, the
swarm nodes will be running Ubuntu 15.04. If you open the Vagrantfile, you'll notice that Swarm master and nodes have the following line:
d.vm.box = "ubuntu/vivid64"