rfc050-resource-actions.md

RFC	Title	Author	Status	Type
50	Resource Actions	John Keiser <[email protected]>	Final	Standards Track

Resource Actions

In this proposal, we allow actions to be specified as recipes, directly in resources.

Motivation

As a Chef user,
I want to be able to write actions in resources,
so that I don't have to learn and reason about `Provider`s (less friction).

As a Chef user,
I want to be able to write actions in resources,
so that I don't have to switch contexts to understand what resources do.

As a Chef user,
I want actions to be specified as recipes by default,
so that I can use concepts I already know to create good test-and-set resources.

Specification

To create an action on a resource, users specify action <action> do ... end. The recipe in between the do ... end block will be run when the action is performed.

class MyResource < Chef::Resource::LWRPBase
  attribute :path, name_attribute: true
  attribute :content
  attribute :mode

  action :create do
    ruby_block "Update content of #{path}" do
      only_if { content != IO.read(path) }
      block { IO.write(path, content) }
    end

    execute "Update mode of #{path}" do
      not_if { File.stat(path).mode == mode }
      command "chmod #{mode} #{path}"
    end
  end
end

There is no change to providers or the way we run actions. This is just a way of defining a provider without having to type or think about the word. Providers do not go away, so much as become a secondary concept, a sort of house for the primary concept of actions.

action will work for any resource extending from Chef::Resource.

Action details

Action recipe execution

The action recipe works like a Chef run, in that it is an isolated resource collection and runs actions and notifications the same way as a top level Chef run.

• The entire action recipe is compiled (just like a normal recipe) before converging.
• This compile happens when the action is run, not when the parent resource is declared.
• Delayed and immediate notifications are local to the action.

This is equivalent to what use_inline_resources in an LWRP does, and we will keep them orthogonal as much as possible.

Action composition and inheritance

If the parent class's action is defined using action, you may call super() to call the parent class's version of the current action.

class MyFile < Chef::Resource::File
  action :create do
    puts "I am a file yo"
    super()
  end
end

Changes to existing things

Resource

We add the following public API to Resource:

• self.action(action, class: nil, &block): creates a handler for the given action

And modify the following:

• allowed_actions: defaults to all actions defined by action, including any actions from superclasses.
• default_action: defaults to the first defined action in the class or superclasses, with the exception of :nothing.

Being defined by the action keyword, this is backwards compatible: neither of these definitions change anything about resources that have providers.

Copyright

This work is in the public domain. In jurisdictions that do not allow for this, this work is available under CC0. To the extent possible under law, the person who associated CC0 with this work has waived all copyright and related or neighboring rights to this work.