1. Client Metadata

Clients are differentiated in terms of several types of
metadata. These types (from least to most specific) are:

- image : the binary compatibility domain of the machine (like
       debian-3.1 or redhat-7.3)
- classes : a host can belong to multiple classes. Classes are used to
       derive the set of software to install on a particular client. 
- bundles: bundles are a sets of related bits of
       configuration. Generally, each bundle provides some piece of
       discrete functionality.
- attributes : attributes can be used to further differentiate
       bundles, or client configurations and are bundle scoped. A host
       may have the webserver.ssl attribute if it is supposed to provide
       ssl/https services in addition to normal port 80 http service. 
- hostname : this is kind of obvious