There must be a way to describe clusters.
If your organization only has a single machine with a single application, then you may not need to describe what a cluster deployment of your application would look like. Unfortunately (or fortunately, depending on your outlook), the reality is normally that your applications are spread out over a set of machines, virtual or physical.
All of the systems that we'll be working with in this chapter support this idea in different ways. Puppet has an extensive system that allows machines to have different roles that, in turn, imply a set of packages and configurations. Ansible and Salt have these systems as well. The container-based Docker system has an emerging infrastructure for describing ...
