Classes

Getting Started

Puppet class is just a block of puppet code, which use to declare resources on you system. Class has parameters, which allow you to adapt a class to suit your needs. We will cover variable and parameters in the next section, for now, let's focus on how the abstraction provided by classes allows you to manage complex sets of resources in terms of a single function they serve.

How to use classes?

Definition

First we need to define a class and saving it to a manifest, and Puppet will parse the manifest and remember your class definition.

Invocation

Once you class defined, and we can invoke your class definitions with or with not parameters.

There are two ways to invoke your Puppet class, if you're using Puppet Enterprise Console, and have all your class invocation placed in you module-path, then it will be trigger to invoke every 30 minutes(base on you configuration, which actually executed by puppet agent -t), another way is manually execute puppet apply command like:

puppet apply file-of-puppet-code.pp

For this tutorial, we will just use puppet apply statement as we use demo on puppet node, no Puppet Enterprise Console.

Validation

For any Puppet manifest, we can use Puppet tool parser to validate your code:

puppet parser validate file-of-puppet-code.pp

Singleton

In Puppet, classes are singleton, which means that a class can only be declared once on a given node. In this sense, Puppet's classes are different than the kind of classes you may have encountered in object-oriented programming, which are often instantiated multiple times. Declaring a class multiple times could give Puppet conflicting instructions for how to manage resources on a system.

Learning by Doing

User Creation

Below tutorial will guide you to define a puppet class to create user

Find you module path (For modules, we will discuss in the next section)

Execute below code to print out you module-path

puppet master --configprint modulepath

Which would result:

/etc/puppetlabs/code/environments/production/modules:/etc/puppetlabs/code/modules:/opt/puppetlabs/puppet/modules

/etc/puppetlabs/code/environments/production/modules are used to save user defined modules, or keep modules for your prod environment. /etc/puppetlabs/code/modules is for site specific modules. /opt/puppetlabs/puppet/modules is for modules required by puppet itself.

Go to production module-path:

cd /etc/puppetlabs/code/environments/production/modules

Create a folder

mkdir user_creation/{manifests,examples,files} -p

Class Definition

Create you first class definition by vim user_creation/manifests/init.pp with below content:

class user_creation {
  user {'Erdan':
    ensure => present ,
    home   => '/home/erdan',
    managehome => true,
  }
}

Compose a class invocation, vim user_creation/examples/user.pp with content:

include user_creation

Validation

Validate you class and you class invocation

puppet parser validate user_creation/manifests/init.pp

puppet parser validate user_creation/examples/user.pp

If no error, then no output.

Dry Run

Before applying any changes to your system, it's always a good idea to use the --noop flag to do a 'dry run' of the Puppet agent. This will compile the catalog and notify you of the changes that Puppet would have made without actually applying any of those changes to your system.

puppet apply --noop user_creation/examples/user.pp

If your dry run looks good, go ahead and run puppet apply again without the --noop flag.

Verify

If everything goes on well, then you can see the user created by puppet

cat /etc/passwd|grep erdan

User home also created.

ls /home/erdan