What is a minimum number of servers required for a production-like cluster? I'd say two. If there's only one server, we would not be able to test whether networking and volumes work across nodes. So, it has to be plural. On the other hand, I don't want to push your laptop too much so we'll avoid increasing the number unless necessary.
For the production-like cluster, two nodes should be enough. We should add one more node that we'll use for running tests and building images. The production cluster should probably be a bit bigger since it will have more services running. We'll make it three nodes big. If needed, we can increase the capacity later on. As you already saw, adding nodes to a Swarm cluster is very easy.
By now, we set up a Swarm cluster quite a few times so we'll skip the explanation and just do it through a script.
Note
All the commands from this chapter are available in the 05-continuous-delivery.sh (https://gist.github.com/vfarcic/5d08a87a3d4cb07db5348fec49720cbe...