An introduction to Puppet

Published on 06 Dec 2025 by Adam Lloyd-Jones

The Puppet configuration management system is an influential and widely adopted open-source automation platform designed to manage IT systems, deploy software, and execute complex operations efficiently across diverse infrastructure environments. Since its inception in 2005, Puppet has matured into a foundational tool for implementing Infrastructure as Code (IaC) practices, enabling organizations to manage their entire IT landscape through machine-readable code.

The challenge of configuration management

Historically, system administration relied heavily on manual processes, shell scripts, and complex, proprietary procedures to configure servers. This manual, or “artisan server crafting,” approach suffers from several key problems, becoming increasingly unmanageable beyond a handful of servers:

Tedium and error-proneness: Manually repeating configurations across multiple servers is complicated and tedious, leading to mistakes, omissions, or the loss of configuration consistency.
Configuration drift: Servers inevitably drift apart over time due to ad hoc manual changes, making it difficult to maintain synchronization and ensuring that all machines match the intended state.
Platform divergence: Different operating systems (e.g., Red Hat, Ubuntu, Solaris) require varying command syntax and default values to perform the same task (like creating a user or installing a package), adding massive complexity to manual automation attempts.
Lack of version control: Without an inherent system to track changes, administrators cannot easily roll back configurations to a previous state when problems arise.

Puppet provides a standardized solution to these problems, eliminating the need for administrators to continually reinvent custom scripting solutions. By allowing infrastructure definitions to be expressed as code, Puppet enables IT professionals to adopt programming best practices—such as powerful editing, refactoring tools, and version control—to ensure higher quality and reliability.

Puppet’s core philosophy and architecture

Puppet is fundamentally an interpreter that reads configuration descriptions, known as manifests, and takes the necessary actions on a machine to ensure it conforms to the specified setup.

Declarative language model

The most significant distinction of Puppet is its use of a declarative programming language. Unlike imperative systems that specify a sequential list of steps to execute (like a shell script or traditional scripting language), Puppet manifests declare the desired end state of the system.

When a Puppet manifest is applied:

Puppet checks the current state of the system against the manifest.
If the desired state is already achieved, Puppet performs no action (it is idempotent).
If the state does not match, Puppet executes the minimum necessary commands behind the scenes (e.g., running apt-get or useradd) to enforce the desired configuration.

This means the manifest is an executable specification that can be run repeatedly, yielding the same result every time, regardless of the platform differences, because Puppet handles the low-level OS-specific commands implicitly.

Master-agent architecture

Puppet typically operates on a Master-agent architecture, although alternative masterless configurations are also supported.

Control node (Master): The server where the Puppet code resides and where manifests are compiled into catalogs. The master also functions as the central Certificate Authority (CA) for the infrastructure.
Managed nodes (Agents): Client machines running the Puppet agent software. These agents communicate securely over SSH or WinRM (for Windows) with the master.
Workflow: The agent initiates contact, sends facts (metadata about the host, e.g., OS, IP, hardware) to the master, and requests a catalog (the compiled manifest specific to that node). The agent then applies the catalog locally.

Core functions: Resources, classes, and definitions

Puppet manifests define configuration in terms of resources, which are the fundamental building blocks (e.g., a file, a user, a service), and their associated attributes, which describe how they should be configured (e.g., the content, the state, the permissions).

Resource management functions

Puppet provides core resource types to manage all facets of the operating system:

Package Management: The package resource installs, updates, or removes software using the native system package manager (e.g., APT on Ubuntu or Yum/DNF on Red Hat). The ensure attribute dictates the state, accepting values like installed, absent, latest, or a specific version number.
Service Management: The service resource manages daemons or background processes. The ensure attribute determines its state (running or stopped), while the enable attribute controls whether the service starts during system boot (true or false).
File and Directory Management: The file resource manages files, ownership, permissions, and directories. The file content can be supplied directly using the content attribute, or pulled from the Puppet repository using the source attribute, often specified as a URI like puppet:///modules/MODULENAME/FILENAME. To copy an entire directory tree, the recurse => true attribute is used,.
User Management: The user resource creates, removes, or modifies user accounts, using attributes such as comment, home, and managehome. To remove an account, ensure => absent is specified.
Access Control (SSH): The ssh_authorized_key resource manages user public keys, which is the secure, preferred method for remote access rather than passwords,.
Command Execution: The exec resource runs arbitrary system commands. This feature is commonly combined with attributes like creates (to achieve idempotency, running only if a target file doesn’t exist) or conditional attributes like unless or onlyif to control execution.

Organizing code: Modules, classes, and definitions

To maintain readable and scalable code, Puppet provides strict structures for organizing resources:

Modules: Collections of related resources, classes, definitions, and data files (like templates) grouped under a specific name (e.g., an nginx module).
Classes: Named, reusable bundles of resources, typically defined within a module’s manifests/init.pp file. Classes are singletons, meaning Puppet enforces only one instance of a given class on any node, making them ideal for managing system-wide effects (like installing a web server). They are applied using the include keyword.
Definitions: Created using the define keyword, definitions are used for sections of code that need to be instantiated multiple times on a single node. They function like functions or subroutines in traditional scripting, reducing redundant code blocks that differ only by specific parameters.

Dependency management

The order in which resources are applied is governed by dependency relationships:

require: Explicitly states that resource B must be applied before resource A. For instance, the Nginx service requires the Nginx package to be installed first.
notify: Creates an implied dependency. If resource A notifies resource B, B is applied after A. This is commonly used for configurations, where a file change (file resource) notifies the corresponding service (service resource) to restart (service restart). The complementary pattern is often referred to as the package-file-service pattern.

Advanced automation and scaling techniques

For large-scale or complex installations, Puppet offers several advanced tools and strategies to ensure performance, scalability, and maintainability.

Scaling and architecture

The default single Puppetmaster setup (WEBrick) is generally only suitable for small environments (often cited as less than 50–100 nodes). Scaling Puppet involves segmenting the master’s workload into several distinct functions, often running on dedicated servers:

Catalog Compilation: This is the most computationally intensive task and is often distributed across a pool of worker machines behind a proxy/load balancer (like Nginx or Apache).
Certificate Signing (CA): Kept separate, sometimes with hot spares, to manage all SSL certificate requests.
Reporting and Storeconfigs (PuppetDB): Separated onto dedicated hosts. PuppetDB is the recommended component for storing the reports and the catalog data,.

Data separation and Hiera

To keep module code clean, generic, and reusable, configuration data specific to hosts, environments, or roles should be separated from the module logic.

Hiera: A key tool in Puppet for separating data from code. Hiera uses a configurable hierarchy based on facts (such as ::hostname, ::osfamily, or custom facts) to look up configuration values. This allows administrators to set specific variables or even apply specific classes using functions like hiera_include based solely on the characteristics of the node.

Exported resources with PuppetDB

The storage component, PuppetDB, enables a powerful feature known as Exported Resources.

Functionality: Exported resources allow a resource definition created on one managed node to be stored in PuppetDB and subsequently collected and instantiated (realized) by another managed node across the infrastructure.
Use Cases: This is critical for configuring peer-to-peer relationships that cannot be easily managed through simple dependency chains. Examples include automatically updating firewall rules on database servers to allow access only from authenticated application servers, or dynamically configuring a central DNS server with the host entries of all managed nodes. Resources are declared using @@ and collected using the <<| |>> syntax.

Puppet vs. other automation tools

While Puppet is a leading configuration management tool, it is often compared to others like Chef and SaltStack, and increasingly, to Ansible.

Feature	Puppet	Ansible
Architecture	Typically Master-Agent,.	Agentless (push-out model),,.
Language	Declarative language/DSL,.	Primarily imperative (sequence of commands), with some declarative modules,.
Learning Curve	Steeper due to the specific declarative language.	Simpler and easier entry point due to YAML configuration.
Execution	Enforces eventual consistency by polling the master,.	Runs tasks sequentially upon execution (imperative flow).
Orchestration	Originally focused on configuration state.	Designed as an orchestration tool from the beginning.

Puppet excels when rigid state management and long-term policing of configuration are the primary requirements, leveraging its established Master-Agent framework and strong declarative language principles.

Puppet’s powerful declarative resource model, combined with advanced data separation (Hiera), sophisticated scaling mechanisms, and features like Exported Resources, provides the tooling necessary to automate complex enterprise-grade environments with consistency and minimal manual intervention. The time invested in mastering its core principles is rewarded with high system reliability and streamlined operations across the entire server lifecycle.

Adam Lloyd-Jones

Adam is a privacy-first SaaS builder, technical educator, and automation strategist. He leads modular infrastructure projects across AWS, Azure, and GCP, blending deep cloud expertise with ethical marketing and content strategy.