Puppet Classes

 • Classes are named blocks of Puppet code that are stored in modules for later use and are not applied until they are invoked by name

• They can be added to a node’s catalog by either declaring them in your manifests or assigning them from an ENC

• Classes generally configure large or medium-sized chunks of functionality, such as all of the packages, config files, and services needed to run an application

• Classes are containers of different resources. Since Puppet 2.6 they can have parameters


Example of Class

class mysql ( root_password => 'default_value', port => '3306', ) 

{ package { 'mysql-server': ensure => present, } 

service { 'mysql': ensure => running, } [...] } 

Note : that when we define a class we just describe what it does and what parameters it has, we don't actually add it and its resources to the catalog.


Defining Classes

# A class with no parameters 

class base::linux 

{ file { '/etc/passwd': owner => 'root', group => 'root', mode => '0644', }

 file { '/etc/shadow': owner => 'root', group => 'root', mode => '0440', } 

}


Defining Classes

# A class with parameters 

class apache (String $version = 'latest') 

{ package {'httpd': ensure => $version, # Using the class parameter from above before => File['/etc/httpd.conf'], } 

file {'/etc/httpd.conf': ensure => file, owner => 'httpd', content => template('apache/httpd.conf.erb'), # Template from a module } 

service {'httpd': ensure => running, enable => true, subscribe => File['/etc/httpd.conf'], } 

}


Class Parameters & Variables

• Parameters allow a class to request external data. If a class needs to configure itself with data other than facts, that data should usually enter the class via a parameter

• Each class parameter can be used as a normal variable inside the class definition

• The values of these variables are not set with normal assignment statements or looked up from top or node scope; instead, they are set based on user input when the class is declared

• If a class parameter lacks a default value, the module’s user must set a value themselves

• You should supply defaults wherever possible

• Each parameter can be preceded by an optional data type

• If included, Puppet will check the parameter’s value at runtime to make sure that it has the right data type, and raise an error if the value is illegal

• If no data type is provided, the parameter will accept values of any data type

• The special variables $title and $name are both set to the class name automatically, so they can’t be used as parameters


Class Location

• Class definitions should be stored in modules. Puppet is automatically aware of classes in modules and can autoload them by name.

• Classes should be stored in their module’s manifests/ directory as one class per file, and each filename should reflect the name of its class

• A class definition statement isn’t an expression and can’t be used where a value is expected.

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