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dynamic-attributes (5) Versions 2.1.0

Interprets and Rewrites Node Attributes

cookbook 'dynamic-attributes', '~> 2.1.0'
cookbook 'dynamic-attributes', '~> 2.1.0', :supermarket
knife cookbook site install dynamic-attributes
knife cookbook site download dynamic-attributes
Quality 50%

Dynamic Attributes


Interprets and rewrites node attributes defined in roles (and only roles!) to provide more dynamicity. For instance, it can be used to get the value of the fqdn in a role by setting an attribute to "node['fqdn']". This cookbook will replace "node['fqdn']" by its true value at execution (in compile phase) so it is available to other cookbooks. This allows a role to be more shareable between nodes.

Different methods of substitution are available. Each method has its own recipe but all are included by default recipe.

It can also generate files in a given format from content specified in attributes, and more when combined with replace/eval feature.

Known limitation: derived attributes defined in attribute files will not read the rewritten values. This is because attribute files are initialized before recipes are compiled, so before the substitutions take place. This will probably not be fixed as it is actually a feature to do the substitution during the cookbook compilation phase, so you may use as source an attribute defined in some other cookbook. Moreover, this limitation should not be encountered very often and can be easily overcome by redefining the derived attributes.


Cookbooks and gems

Declared in [metadata.rb](metadata.rb) and in [Gemfile](Gemfile).


It should work on any platform as it is pure ruby. However it is just tested with kitchen on a Centos 7 docker image.


To be started

Add the default recipe in you runlist in any position you want, knowing that a source must be defined before and a reader must be after this cookbook compile phase to see the effect in compile phase.

You may also want to tweak attributes (like whitelisting).

Read recipes documentation for more details.

Known limitations

Redefining a default attribut in cookbook attribute files from node attribute will lead to an incorrect behavior: both original and rewritten attributes will be read.

Ex: in something/attributes/some.rb: ruby default['something'] = node.default['something']

Errors / Logging

All replace/eval are run before raising any errors (which will fail the chef run). Moreover, all successful substitutions are logged at INFO level.


This cookbook is tested with kitchen on a Centos 7 docker image. A test cookbook is used to extract attributes after default recipe has run.

For more information, see [.kitchen.yml](.kitchen.yml) and [test](test) directory.


Configuration is done by overriding default attributes. All configuration keys have a default defined in [attributes/default.rb](attributes/default.rb). Please read it to have a comprehensive view of what and how you can configure this cookbook behavior.



Include replace then eval and file recipes. So it performs all substitutions, one after another before generating any requested file. Attribute key (keys in hashmaps) are also modified if needed.

Note that by default, eval has no effect as no attribute is whitelisted. In contrary, replace is executed on all attributes.

You can look at examples defined as tests for more information.


Replace (recursively) whitelisted (default: all) attributes of the form "node['foo']['bar']" to their "true" value. It is not a string interpolation nor a substring replacement: it will work solely if the attributes value is exactly "node['something']".

If the target value does not exist (like "node['doesnotexist']"), it keeps the current value (that is the string "node['doesnotexist']").

You can look at examples defined as tests for more information.


Evaluate (with the use of eval method) whitelisted (default: none) attributes as if there were referenced in a double-quote string and set the result as new attribute value. For instance, an attribute with value "1+#{1+1}" will be rewrited as "1+2" (as it would be in ruby).

Be careful with this substitution method as you can execute any ruby code. Be sure to whitelist only the attributes you need.

You can look at examples defined as tests for more information.


Generate a file (with file resource) from attributes in a given format.

By combining it with replace/eval feature, the files can be generated from any attributes or even from a data bag. This can be used to generate configuration file or secrets file (with encrypted an data bag for instance).

You can look at examples defined as tests for more information.


Provide implementation of the different methods: eval and replace.






Please read carefully []( before making a merge request.

License and Author

Copyright (c) 2016 Sam4Mobile, 2017-2018

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.

Dependent cookbooks

This cookbook has no specified dependencies.

Contingent cookbooks

There are no cookbooks that are contingent upon this one.




  • feat: can create dir when generating a file
  • fix: display errors when not using default recipe



  • feat: make eval return real object instead of string
    • If the evalued code return a hash, the attribute will be a hash and not the string representation of the hash. Same for an int.
    • WARNING: this may break existing code relying on previous (broken) behavior. Add .to_s to evalued code if you need.
  • feat: raise an error if replaced attr is not found
    • WARNING(breaking change): raise an exception if target value does not exist
  • feat: aggregate all errors including eval ones before raising them
  • feat: output all substitutions with
  • feat: add recipe to generate a file from attrs
    • You can choose a predefined format (txt, yaml, json, ini, xml) or use the dynamic eval to generate the string you want.
  • chore: set chef version to 14 (for ruby 2.5)


  • test: unchefize attributes before marshaling them
  • style(rubocop): disable InterpolationCheck in test
  • test: include .gitlab-ci.yml from test-cookbook
  • test: replace deprecated require_chef_omnibus


  • doc: use karma for git format in contributing
  • doc: add a known limitation
  • style(rubocop): fix some style issues
  • chore: add 2018 to copyright notice
  • chore: set generic maintainer & helpdesk email



  • Handover maintenance to update emails, copyright, urls, etc.


  • Use Continuous Integration with gitlab-ci with latest template [20170405]


  • Fix all rubocop offenses
  • Use cookbook_name alias in attributes


  • Fix non-intuitive behavior with escaped double-quote, add a test-case
  • Simplify the whitelist defined for eval tests
  • Clarify documentation on eval recipe


  • Initial version, supports eval and replace with configurable whitelists

Collaborator Number Metric

2.1.0 failed this metric

Failure: Cookbook has 1 collaborators. A cookbook must have at least 2 collaborators to pass this metric.

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