cookbook 'poise', '= 2.0.0'
poise
(25) Versions
2.0.0
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Helpers for writing extensible Chef cookbooks.
cookbook 'poise', '= 2.0.0', :supermarket
knife supermarket install poise
knife supermarket download poise
Poise
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.
Contingent cookbooks
Foodcritic Metric
2.0.0 failed this metric
FC011: Missing README in markdown format: /tmp/cook/5c64cb6810f928288fba6472/poise/README.md:1
FC031: Cookbook without metadata file: /tmp/cook/5c64cb6810f928288fba6472/poise/metadata.rb:1
FC045: Consider setting cookbook name in metadata: /tmp/cook/5c64cb6810f928288fba6472/poise/metadata.rb:1
2.0.0 failed this metric
FC031: Cookbook without metadata file: /tmp/cook/5c64cb6810f928288fba6472/poise/metadata.rb:1
FC045: Consider setting cookbook name in metadata: /tmp/cook/5c64cb6810f928288fba6472/poise/metadata.rb:1
