Book: Pulling string with Puppet

Excellent book by James Turnbull, which explains in clear words the concepts behind Puppet.
Resources and Collections (classes)
Idempotence; RAL (Resource Abstraction Layer) and Providers
Installation of Puppet, certificates, site.pp
Class inheritance and override. Difference between a class and a definition.
Variable scope. if, case, conditional selector.
node definition, default, node inheritance; virtual and exported resources;
filebucket, tidy
reporting, external node classifier (with examples). Facter and Custom facts.