Classes

Create a class by writing a class definition in a manifest (.pp) file. Store class manifests in the manifests/ directory of a module. Define only one class in a manifest, and give the manifest file the same name as the class. Puppet automatically loads any classes that are present in a valid module. See module fundamentals to learn more about module structure and usage.

A class contains all of its resources. This means any relationships formed with the class as a whole is extended to every resource in the class. Every resource in a class gets automatically tagged with the class’s name and each of its namespace segments.

Classes can contain other classes, but you must use the contain function to explicitly specify when a class is contained. For more information, see the documentation about containing classes. A contained class is automatically tagged with the name of its container.

class base::linux {
  file { '/etc/passwd':
    owner => 'root',
    group => 'root',
    mode  => '0644',
  }
  file { '/etc/shadow':
    owner => 'root',
    group => 'root',
    mode  => '0440',
  }
}

class apache (String $version = 'latest') {
  package {'httpd':
    ensure => $version, # Using the version 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 and variables

Parameters allow a class to request external data. If a class needs to use data other than facts for configuration, use a parameter for that data.

You can use class parameters as normal variables inside the class definition. The values of these variables are set based on user input when the class is declared, rather than with normal assignment statements.

Supply default values for parameters whenever possible. If a class parameter lacks a default value, the parameter is considered required and the user must set a value, either in external data or as an override.

If you set a data type for each parameter, Puppet checks the parameter's value at runtime to make sure that it is the correct data type, and raises an error if the value is illegal. If you do not provide a data type for a parameter, the parameter accepts values of any data type.

The variables $title and $name are both set to the class name automatically, so you can't use them as parameters.

Setting class parameter defaults with Hiera data

To set class parameter defaults with Hiera data in your modules, set up a hierarchy in your module's hiera.yaml file and include the referenced data files in the data directory.

# ntp/hiera.yaml
---
version: 5
defaults:
  datadir: data
  data_hash: yaml_data
hierarchy:
  - name: "OS family"
    path: "os/%{facts.os.family}.yaml"

  - name: "common"
    path: "common.yaml"

# ntp/data/common.yaml
---
ntp::autoupdate: false
ntp::service_name: ntpd

# ntp/data/os/Debian.yaml
ntp::service_name: ntp

You can declare classes in node definitions, at top scope in the site manifest, and in other classes or defined types. Classes are singletons — although a given class can behave very differently depending on how its parameters are set, the resources in it are evaluated only once per compilation. You can also assign classes to nodes with an external node classifier (ENC) .

Puppet has two main ways to declare classes: include-like and resource-like. Include-like declarations are the most common; they are flexible and idempotent, so you can safely repeat them without causing errors. Resource-like declarations are mostly useful if you want to pass parameters to the class but can't or don't use Hiera. Most ENCs assign classes with include-like behavior, but others assign them with resource-like behavior. See the ENC interface documentation or the documentation of your specific ENC for details.

Include-like declarations

Include-like resource declarations allow you to declare a class multiple times — but no matter how many times you add the class, it is added to the catalog only once. This allows classes or defined types to manage their own dependencies and allows you create overlapping role classes, in which a given node can have more than one role.

Include-like behavior relies on external data and defaults for class parameter values, which allows the external data source to act like cascading configuration files for all of your classes.

You can declare a class with this behavior with one of three functions: include, require, and contain.

The include function

This function uses include-like behavior, so you can make multiple declarations and Puppet relies on external data for parameters.

include base::linux

include Class['base::linux']

include base::linux, apache

$my_classes = ['base::linux', 'apache']
include $my_classes

The require function

The require function declares one or more classes, then causes them to become a dependency of the surrounding container. This function uses include-like behavior, so you can make multiple declarations, and Puppet relies on external data for parameters.

define apache::vhost (Integer $port, String $docroot, String $servername, String $vhost_name) {
  require apache
  ...
}

The contain function

The contain function is used inside another class definition to declare one or more classes and contain those classes in the surrounding class. This enforces ordering of classes. When you contain a class in another class, the relationships of the containing class extend to the contained class as well. For details about containment, see the documentation on containing classes.

This function uses include-like behavior, so you can make multiple declarations, and Puppet relies on external data for parameters.

class ntp {
  file { '/etc/ntp.conf':
    ...
    require => Package['ntp'],
    notify  => Class['ntp::service'],
  }
  contain ntp::service
  package { 'ntp':
    ...
  }
}

For example, if a resource has a before relationship with the ntp class, that resource will also be applied before the ntp::service class. Similarly, any resource that forms a require relationship with ntp will be applied after ntp::service.

The hiera_include function

The legacy Hiera function hiera_include has been deprecated. In Hiera 5 and later, instead of using hiera_include use lookup with the include function. For example: use lookup('classes', {merge => unique}).include instead of hiera_include('classes').

Resource-like declarations

Resource-like class declarations require that you declare a given class only once. They allow you to override class parameters at compile time — for any parameters you don't override, Puppet falls back to external data.

Resource-like declarations look like normal resource declarations, using the class pseudo-resource type. You can provide a value for any class parameter by specifying it as a resource attribute.

class {'base::linux':}

class {'apache':
  version => '2.2.21',
}