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poise (24) Versions 2.0.1

Helpers for writing extensible Chef cookbooks.

Berkshelf/Librarian
Policyfile
Knife
cookbook 'poise', '= 2.0.1'
cookbook 'poise', '= 2.0.1', :supermarket
knife cookbook site install poise
knife cookbook site download poise
README
Dependencies
Changelog
Quality 0%

Poise

Build Status Gem Version Cookbook Version Coverage Gemnasium License

What is Poise?

The poise cookbook is a set of libraries for writing reusable cookbooks. It providers helpers for common patterns and a standard structure to make it easier to create flexible cookbooks.

Writing your first resource

Rather than LWRPs, Poise promotes the idea of using normal, or "heavy weight" resources, while including helpers to reduce much of boilerplate needed for this. Each resource goes in its own file under libraries/ named to match the resource, which is in turn based on the class name. This means that the file libraries/my_app.rb would contain Chef::Resource::MyApp which maps to the resource my_app.

An example of a simple shell to start from:

class Chef
  class Resource::MyApp < Resource
    include Poise

    actions(:enable)

    attribute(:path, kind_of: String)
    ... # Other attribute definitions
  end

  class Provider::MyApp < Provider
    include Poise

    def action_enable
      converge_by("enable resource #{new_resource.name}") do
        notifying_block do
          ... # Normal Chef recipe code goes here
        end
      end
    end
  end
end

Starting from the top, first we declare the resource class, which inherits from Chef::Resource. This is similar to the resources/ file in an LWRP, and a similar DSL can be used. In order to load the helpers into the class, we include the Poise mixin. Then we use the familiar DSL, though with a few additions we'll cover later.

Then we declare the provider class, again similar to the providers/ file in an LWRP. We include the Poise mixin again to get access to all the helpers. Rather than use the action :enable do ... end DSL from LWRPs, we just define the action method directly, and use the converge_by method to provide a description of what the action does. The implementation of action comes from a block of recipe code wrapped with notifying_block to capture changes in much the same way as use_inline_resources, see below for more information about all the features of notifying_block.

We can then use this resource like any other Chef resource:

my_app 'one' do
  path '/tmp'
end

Helpers

While not exposed as a specific method, Poise will automatically set the resource_name based on the class name.

Notifying Block

As mentioned above, notifying_block is similar to use_inline_resources in LWRPs. Any Chef resource created inside the block will be converged in a sub-context and if any have updated it will trigger notifications on the current resource. Unlike use_inline_resources, resources inside the sub-context can still see resources outside of it, with lookups propagating up sub-contexts until a match is found. Also any delayed notifications are scheduled to run at the end of the main converge cycle, instead of the end of this inner converge.

This can be used to write action methods using the normal Chef recipe DSL, while still offering more flexibility through subclassing and other forms of code reuse.

Include Recipe

In keeping with notifying_block to implement action methods using the Chef DSL, Poise adds an include_recipe helper to match the method of the same name in recipes. This will load and converge the requested recipe.

Resource DSL

To make writing resource classes easier, Poise exposes a DSL similar to LWRPs for defining actions and attributes. Both actions and default_action are just like in LWRPs, though default_action is rarely needed as the first action becomes the default. attribute is also available just like in LWRPs, but with some enhancements noted below.

One notable difference over the standard DSL method is that Poise attributes can take a block argument.

Template Content

A common pattern with resources is to allow passing either a template filename or raw file content to be used in a configuration file. Poise exposes a new attribute flag to help with this behavior:

attribute(:name, template: true)

This creates four methods on the class, name_source, name_cookbook, name_content, and name_options. If the name is set to '', no prefix is applied to the function names. The content method can be set directly, but if not set and source is set, then it will render the template and return it as a string. Default values can also be set for any of these:

attribute(:name, template: true, default_source: 'app.cfg.erb',
          default_options: {host: 'localhost'})

As an example, you can replace this:

if new_resource.source
  template new_resource.path do
    source new_resource.source
    owner 'app'
    group 'app'
    variables new_resource.options
  end
else
  file new_resource.path do
    content new_resource.content
    owner 'app'
    group 'app'
  end
end

with simply:

file new_resource.path do
  content new_resource.content
  owner 'app'
  group 'app'
end

As the content method returns the rendered template as a string, this can also be useful within other templates to build from partials.

Lazy Initializers

One issue with Poise-style resources is that when the class definition is executed, Chef hasn't loaded very far so things like the node object are not yet available. This means setting defaults based on node attributes does not work directly:

attribute(:path, default: node['myapp']['path'])
...
NameError: undefined local variable or method 'node'

To work around this, Poise extends the idea of lazy initializers from Chef recipes to work with resource definitions as well:

attribute(:path, default: lazy { node['myapp']['path'] })

These initializers are run in the context of the resource object, allowing complex default logic to be moved to a method if desired:

attribute(:path, default: lazy { my_default_path })

def my_default_path
  ...
end

Option Collector

Another common pattern with resources is to need a set of key/value pairs for configuration data or options. This can done with a simple Hash, but an option collector attribute can offer a nicer syntax:

attribute(:mydata, option_collector: true)
...

my_app 'name' do
  mydata do
    key1 'value1'
    key2 'value2'
  end
end

This will be converted to {key1: 'value1', key2: 'value2'}. You can also pass a Hash to an option collector attribute just as you would with a normal attribute.

Sponsors

The Poise test server infrastructure is generously sponsored by Rackspace. Thanks Rackspace!

License

Copyright 2013-2015, Noah Kantrowitz

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

Dependent cookbooks

This cookbook has no specified dependencies.

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Changelog

v2.0.1

  • Make the ChefspecHelpers helper a no-op if chefspec is not already loaded.
  • Fix for finding the correct cookbook for a file when using vendored gems.
  • New flag for the OptionCollector helper, parser:
class Resource < Chef::Resource
  include Poise
  attribute(:options, option_collector: true, parser: proc {|val| parse(val) })

  def parse(val)
    {name: val}
  end
end
  • Fix for a possible infinite loop when using ResourceProviderMixin in a nested module structure.

v2.0.0

Major overhaul! Poise is now a Halite gem/cookbook. New helpers:

  • ChefspecMatchers – Automatically create Chefspec matchers for Poise resources.
  • DefinedIn – Track which file (and cookbook) a resource or provider is defined in.
  • Fused – Experimental support for defining provider actions in the resource class.
  • Inversion – Support for end-user dependency inversion with providers.

All helpers are compatible with Chef >= 12.0. Chef 11 is now deprecated, if you need to support Chef 11 please continue to use Poise 1.

v1.0.12

  • Correctly propagate errors from inside notifying_block.

v1.0.10

  • Fixes an issue with the LWRPPolyfill helper and false values.

v1.0.8

  • Delayed notifications from nested converges will still only run at the end of the main converge.

v1.0.6

  • The include_recipe helper now works correctly when used at compile time.

v1.0.4

  • Redeclaring a template attribute with the same name as a parent class will inherit its options.

v1.0.2

  • New template attribute pattern.
attribute(:config, template: true)

...

resource 'name' do
  config_source 'template.erb'
end

...

new_resource.config_content

v1.0.0

  • Initial release!

Foodcritic Metric
            

2.0.1 failed this metric

FC031: Cookbook without metadata file: /tmp/cook/bfa2b191929a4dfdb134d248/poise/metadata.rb:1
FC045: Consider setting cookbook name in metadata: /tmp/cook/bfa2b191929a4dfdb134d248/poise/metadata.rb:1