Puppet: Mastering Infrastructure Automation

Using the type system

Older Puppet versions supported a small set of data types only: Bool, String, Array, and Hash. The Puppet DSL had almost no functionality to check for consistent variable types. Consider the following scenario.

A parameterized class enables other users of your code base to change the behavior and output of the class:

class ssh (
  $server = true,
){
  if $server {
    include ssh::server
  }
}

This class definition checks whether the server parameter has been set to true. However, in this example, the class was not protected from wrong data usage:

class { 'ssh':
  server => 'false',
}

In this class declaration, the server parameter has been given a string instead of a bool value. Since the false string is not empty, the if $server condition ...