Custom Resource Guide

Chef Infra Client ships with over 150 built-in resources for managing system configuration such as directory, remote_file, and windows_firewall. With Custom Resources you can extend the built-in capabilities of Chef Infra Client to create reusable resources for use anywhere in your infrastructure.

• Ship directly in cookbooks
• Leverage Chef Infra Client built-in resources and any additional custom Ruby code (if needed)
• Behave the same as existing built-in resources in your recipes

Syntax

The layout for a custom resource is:

provides :resource_name

property :property_name, RubyType, default: 'value'

action :action_a do
 # a mix of built-in Chef Infra resources and Ruby
end

action :action_b do
 # a mix of built-in Chef Infra resources and Ruby
end

The first action listed is the default action.

Write a Custom Resource

You’ll write the code for a custom resource in a Ruby file and located in a cookbook’s /resources directory (you need to generate the resource first). This code:

• Declares the properties of the custom resource
• Loads current state of properties for existing resources
• Defines each action the custom resource may take

Generate a Custom Resource

The resources directory does not exist by default in a cookbook. Generate the resources directory and a resource file from the chef-repo/cookbooks directory with the command:

chef generate resource PATH_TO_COOKBOOK RESOURCE_NAME

For example, this command generates a site resource in the custom_web cookbook:

chef generate resource cookbooks/custom_web site

The custom_web cookbook directory with a custom resource has the structure:

- cookbooks
  - custom_web
    - recipes
      - default.rb
    - resources
      - site.rb
    - test
      - integration
        - default
          - default_test.rb
    - .gitignore
    - CHANGELOG.md
    - chefignore
    - kitchen.yml
    - LICENSE
    - metadata.rb
    - Policyfile.rb
    - README.md

Example Resource

This example site uses Chef Infra’s built-in file, service and package resources, and includes :create and :delete actions. It also assumes the existence of a custom httpd template. The code in this custom resource is similar to a typical recipe because it uses built-in Chef Infra Client resources, with the addition of the property and actions definitions for this custom resource.

provides :site

property :homepage, String, default: '<h1>Hello world!</h1>'

action :create do
  package 'httpd'

  service 'httpd' do
    action [:enable, :start]
  end

  file '/var/www/html/index.html' do
    content new_resource.homepage
  end
end

action :delete do
  package 'httpd' do
    action :remove
  end

  file '/var/www/html/index.html' do
    action :delete
  end
end

where

• site is the name of the custom resource. The provides statement makes the custom resource available for use recipes.
• homepage sets the default HTML for the index.html file with a default value of '<h1>Hello world!</h1>'
• the action block uses the built-in collection of resources to tell Chef Infra Client how to install Apache, start the service, and then create the contents of the file located at /var/www/html/index.html
• action :create is the default resource (because it is listed first); action :delete must be called specifically (because it is not the default action)

Once written, you can use a custom resource may be used in a recipe with the same syntax as Chef Infra Client built-in resources.

Syntax

Call a resource in a recipe by its resource_name. For example:

site 'foo'

Learn More

Learn Chef interactive tutorial: Extending Chef Infra: Custom Resources

See the Custom Resources Glossary for a description of available methods.