Dan Bode - Puppet Types and Providers

Puppet is a configuration management tool that has enjoyed phenomenal growth over the last few years. Propelled by increasing demands on sysadmins, and the continuous growth of infrastructure (both physical and virtual), Puppet has been one of the key technology components of the DevOps movement. This cultural shift focuses on breaking down the silo between development and operations. Tools like Puppet are important to this movement because it allows application deployment knowledge to be expressed as code to build automated release platforms.

Puppet is also helping lead the path towards software-defined infrastructure (or infrastructure as code). As more systems in data centers support better APIs, the importance of centralized configuration management increases. Puppet is leading this trend by leveraging its model to manage more than the roles of individual systems. It also supports network devices, load balancers, and managing virtual machine instances.

All system configurations in Puppet are expressed as resources that model complex configurations using Puppets Domain Specific Language (DSL). Puppet supports a large set of native resources for modeling the desired state of a system. Resources already exist for managing most common elements of a system (users, groups, packages, services). These native resources are implemented in Ruby using Puppets type and provider APIs.

The power of Puppet lies in its ability to manage the state of complex systems using this simple resource model. This book discusses the highly extensible resource model and the framework around it. It explores the extension points and how to leverage them to expand Puppets functionality.

Puppet has a vibrant user community, and has seen an explosion of content in the last few years. Puppets online documentation and existing books serve as great references for language constructs and architecture. We have always considered the type and provider APIs as one of the most important and least documented aspects of Puppet. This book is aimed at lowering the barrier for writing types and providers by providing sufficient instructions and examples.

Most of what we learned about types and providers has been through trial and error following the evolution of Puppets source code changes. The experience of writing a large number of types and providers has really opened us to the potential of Puppet. Learning how to do it by reading source code, however, has been a long and painful process fraught with many mistakes and poor implementations.

The goal of this book is to explain all of the concepts of types and providers in detail along with many of the lessons we have learned. We hope this helps Puppet users better understand why they should be writing types and providers, and also arm them with enough information on how to properly implement them.

The book walks through examples to demonstrate concepts and also shows the user how to delve into Puppets source code to get a better understanding of how types and providers are implemented internally.

Its also worth noting that when we explore the APIs for developing custom types and providers (in , respectively), we occasionally reimplement functionality that already exists in the Puppet source code. The examples in this book are not intended to be replacement code per sethey are intentionally simplified and intended to serve as an reference on how to implement the important features from the type and provider APIs.