The Docker InfraKit is a tool to create and manage you infrastructure in a declarative and self-healing manner. InfraKit itself more or less only consists of plugins, communicating via unix domain sockets. There are different types of plugins, namely group, instance, and flavour, each with a focus on different layers of infrastructure management. Instance plugins are no surprise here: they manage your physical resources. Whether a physical resource is actually some machine or only a virtual concept, is an implementation detail of the instance plugin.