Open source Puppet 6.11

You'll use Puppet's declarative language to describe the desired state of your system in files called manifests. Manifests describe how to configure your network and operating system resources, such as files, packages, and services. Puppet then compiles those manifests into catalogs, which across your infrastructure.

Catalogs

To configure nodes, the Puppet master compiles configuration information into a catalog, which describes the desired state of a specific agent node. Each agent requests and receives its own individual catalog.

The catalog describes the desired state for every resource managed on a single given node. Whereas a manifest can contain conditional logic to describe specific resource configuration for multiple nodes, a catalog is a static document that describes all of the resources and and dependencies for only one node.

To create a catalog for a given agent, the master compiles:
  • Data from the agent, such as facts or certificates.

  • External data, such as values from functions or classification information from the PE console.

  • Manifests, which can contain conditional logic to describe the desired state of resources for many nodes.

The master resolves all of these elements and compiles a specific catalog for each individual agent. After the agent receives its catalog, it applies any changes needed to bring the agent to the state described in the catalog.

Tip: When you run the puppet apply command on a node, it compiles the catalog locally and applies it immediately on the node where you ran the command.

Agents cache their most recent catalog. If they request a catalog and the master fails to compile one, they fall back to their cached catalog. For detailed information on the catalog compilation process, see the catalog compilation system page.

Resources and classes

A resource describes some aspect of a system, such as a specific service or package. You can group resources together in classes, which generally configure larger chunks of functionality, such as all of the packages, configuration files, and services needed to run an application.

The Puppet language is structured around resource declaration. When you declare a resource, you tell Puppet the desired state for that resource, so that Puppet can add it to the catalog and manage it. Every other part of the Puppet language exists to add flexibility and convenience to the way you declare resources.

Just as you declare a single resource, you can declare a class to manage many resources at once. Whereas a resource declaration might manage the state of a single file or package, a class declaration can manage everything needed to configure an entire service or application, including packages, configuration files, service daemons, and maintenance tasks. In turn, small classes that manage a few resources can be combined into larger classes that describe entire custom system roles, such as "database server" or "web application worker."

To add a class's resources to the catalog, either declare the class in a manifest or classify your nodes. Node classification allows you to assign a different set of classes to each node, based on the node's role in your infrastructure. You can classify nodes with node definitions or by using node-specific data from outside your manifests, such as that from an external node classifier or Hiera.

Manifests

Resources are declared in manifests, Puppet language files that describe how the resources should be configured. Manifests are a basic building block of Puppet and are kept in a specific file structure called a module. You can write your own manifests and modules or download them from Puppet or other Puppet users. 

Manifests can contain conditional logic and declare resources for multiple agents. The master evaluates the contents of all the relevant manifests, resolves any logic, and compiles catalogs. Each catalog defines state for one specific node.

Manifests:

  • Are text files with a .pp extension.

  • Must use UTF-8 encoding.

  • Can use Unix (LF) or Windows (CRLF) line breaks.

When compiling the catalog, the master always evaluates the main manifest first. This manifest, also known as the site manifest, defines global system configurations, such as LDAP configuration, DNS servers, or other configurations that apply to every node. The main manifest can be either a single manifest, usually named site.pp, or a directory containing several manifests, which Puppet treats as a single file. For more details about the main manifest, see the main manifest page.

The simplest Puppet deployment consists of a single main manifest file with a few resources. As you're ready, you can add complexity progressively, by grouping resources into modules and classifying your nodes more granularly.

Manifest example

This short manifest manages NTP. It includes:
  • A case statement that sets the name of the NTP service, depending on which operating system is installed on the agent.

  • A package resource that installs the NTP package on the agent.

  • A service resource that enables and runs the NTP service. This resource also applies the NTP configuration settings from ntp.conf to the service.

  • A file resource that creates the ntp.conf file on the agent in /etc/ntp.conf. This resource also requires that the ntp package is installed on the agent. The contents of the ntp.conf file will be taken from the specified source file, which is contained in the ntp module.

case $operatingsystem {
  centos, redhat: { $service_name = 'ntpd' }
  debian, ubuntu: { $service_name = 'ntp' }
}

package { 'ntp':
  ensure => installed,
}

service { 'ntp':
  name      => $service_name,
  ensure    => running,
  enable    => true,
  subscribe => File['ntp.conf'],
}

file { 'ntp.conf':
  path    => '/etc/ntp.conf',
  ensure  => file,
  require => Package['ntp'],
  source  => "puppet:///modules/ntp/ntp.conf",
  # This source file would be located on the Puppet master at
  # /etc/puppetlabs/code/modules/ntp/files/ntp.conf
}
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