Book Image

Extending Puppet - Second Edition

By : Alessandro Franceschi, Jaime Soriano Pastor
Book Image

Extending Puppet - Second Edition

By: Alessandro Franceschi, Jaime Soriano Pastor

Overview of this book

Puppet has changed the way we manage our systems, but Puppet itself is changing and evolving, and so are the ways we are using it. To tackle our IT infrastructure challenges and avoid common errors when designing our architectures, an up-to-date, practical, and focused view of the current and future Puppet evolution is what we need. With Puppet, you define the state of your IT infrastructure, and it automatically enforces the desired state. This book will be your guide to designing and deploying your Puppet architecture. It will help you utilize Puppet to manage your IT infrastructure. Get to grips with Hiera and learn how to install and configure it, before learning best practices for writing reusable and maintainable code. You will also be able to explore the latest features of Puppet 4, before executing, testing, and deploying Puppet across your systems. As you progress, Extending Puppet takes you through higher abstraction modules, along with tips for effective code workflow management. Finally, you will learn how to develop plugins for Puppet - as well as some useful techniques that can help you to avoid common errors and overcome everyday challenges.
Table of Contents (19 chapters)
Extending Puppet Second Edition
About the Authors
About the Reviewer


Puppet provides different constructs to manage conditionals inside manifests.

Selectors as we have seen, let us set the value of a variable or an argument inside a resource declaration according to the value of another variable. Selectors, therefore, just return values, and are not used to manage conditionally entire blocks of code.

Here's an example of a selector:

$package_name = $::osfamily ? {
  'RedHat' => 'httpd',
  'Debian' => 'apache2',
  default  => undef,

The case statements are used to execute different blocks of code according to the values of a variable. It's recommended to have a default block for unmatched entries. Case statements can't be used inside resource declarations. We can achieve the same result of the previous selector with this case sample:

case $::osfamily {
  'Debian': { $package_name = 'apache2' }
  'RedHat': { $package_name = 'httpd' }
  default: { fail ("Operating system $::operatingsystem not supported") } 

The if, elsif, and else conditionals, like case, are used to execute different blocks of code and can't be used inside resources declarations. We can use any of Puppet's comparison expressions and we can combine more than one for complex patterns matching.

The previous sample variables assignment can also be expressed in this way:

if $::osfamily == 'Debian' {
  $package_name = 'apache2'
} elsif $::osfamily == 'RedHat' {
  $package_name = 'httpd'
} else {
  fail ("Operating system $::operatingsystem not supported")

The unless condition is the opposite of if. It evaluates a Boolean condition and, if it's false, it executes a block of code. The use of unless instead of negating the if condition is more a personal preference, but it shouldn't be used with complex expressions as it reduces readability.