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updatable-attributes (6) Versions 1.1.0

Allow definition of attribute based on other attributes and recomputed on update.

cookbook 'updatable-attributes', '~> 1.1.0', :supermarket
cookbook 'updatable-attributes', '~> 1.1.0'
knife supermarket install updatable-attributes
knife supermarket download updatable-attributes
Quality 25%

Cookbook updatable-attributes

Cookbook Version

Allow to declare attributes computed each time other ones are updated.


This cookbook supports and requires Chef 12.16.23+.


This cookbook leverage built-in Chef features and supports all Platforms.


To compute attributes based on a single attribute path:

on_attribute_update('foo', 'bar') do
  default['blah'] = node['foo']['bar']
# equivalent to
on_attribute_update(%w[foo bar]) do
  default['blah'] = node['foo']['bar']

To compute attributes based on multiple attribute paths:

on_attributes_update(%w[foo bar], 'blah') do
  default['all'] = node['foo']['bar'] + node['blah']
# equivalent to
on_attributes_update(%w[foo bar], %w[blah]) do
  default['all'] = node['foo']['bar'] + node['blah']


Option Default Description
init_on_registration true Evaluate the block on registration.
observe_\parents true Also observe parent attribute updates.
recursion 0 Configure allowed level of recursion.

To debug attributes update

Sometimes it is tricky to understand why an attribute ended-up with its final value.
Chef provides the node.debug_value method, which is already great, but it only prints the state when you call it.

If you need to debug the "lifecycle" of your attributes, you can enable a temporary debug feature simply using the environment variable: DEBUG_ATTRIBUTES_KEYS

The debug feature will evaluate this environment variable as a comma-separated list of attribute's key to watch.
For instance if you want to debug all changes on attributes named "dangerous" and "important" you can do this:

  DEBUG_ATTRIBUTES_KEYS=dangerous,important sudo -E chef-client

As the attributes matching is trivial any attribute key equal to the given values will be logged.
For instance the following attributes changes will be logged:

default['dangerous'] = true
default['a']['dangerous']['setting'] = 42
override['not']['important']['at'] = 'all'

However the matching is case sensitive on the whole string, so these changes won't be logged:

default['almost_dangerous'] = 41
override['very']['Interesting'] = '!'

Finally, please note that the default log level used here is debug, if you want to change that you should use another environement variable: DEBUG_ATTRIBUTES_LOG_LEVEL

For instance to log as warning the use of a dangerous attribute you can do:



  1. Fork the repository on Github
  2. Create a named feature branch (like add_component_x)
  3. Write your change
  4. Write tests for your change (if applicable)
  5. Run the tests, ensuring they all pass
  6. Submit a Pull Request using Github

License and Authors

Copyright 2017 Baptiste Courtois

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

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
See the License for the specific language governing permissions and
limitations under the License.

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