Managing Infrastructure with Puppet

Inheritance and Parameterized Classes

As we saw in the ntp example, classes are great for organizing our configurations, but they can also enhance the reusability of our code. Classes in Puppet, unlike define types, are not like their instanceable namesake in other object-oriented programming languages. They will take parameters and can even inherit structure from other classes, but only one class of a particular name can exist on each node.

We can build a base class that installs our Apache2 package and sets up a service to manage it. We can then inherit from the base and add a couple of special-purpose classes for an Apache with SSL and Apache with PHP. This helps to reduce duplication in our code and makes future changes less onerous:

class http-server {
  package { "apache2": ensure => installed }

  service { "apache2": 
      ensure => running,
      enable => true,
      pattern => "apache2",
      subscribe => Package["apache2"],
      }
  }

class https-server inherits http-server {
  exec { "a2enmod ssl":
      creates => "/etc/apache2/mods-enabled/ssl.load",
      notify => Service["apache2"],
      }
  }
    
class http-php-server inherits http-server {
  package { "libapache2-mod-php5": ensure => installed }

  exec { "a2enmod php5":
      creates => "/etc/apache2/mods-enabled/php5.load",
      notify => Service["apache2"],
      }

  file { "/etc/php5/apache2/php.ini":
      source => "puppet:///modules/apps/php5/php.ini",
      notify => Service["apache2"],
      }
  }

We can also pass parameters into classes when we include them in a node. Say we need to install different package ...