jgedarovich / chef-attribute-debug

A tool to discover where a chef attribute is being set from

A tool to discover where a chef attribute is being set from.

Description

At some point or another when working with chef you'll end up in a situation where it's necessary to unravel how or why a particular attribute is set on a node a certain way. At which point you'll find yourself on a journey through comparing the 15 levels of chef attributes and a nodes runlist - a painful waste of time. debug_value can help by telling you roughly at what level it's being set at, but it's usefulness stops there.

Enter the chef-attribute-debugger. By simply instrumenting an example host in question's client.rb file, one can find the source of where an attribute is being set.

What it is

A series of monkey patches for omnibus chef version 11.18.12 that get applied at the client.rb level that can determine from where an attribute is being set. By monkey patchincg all of the points in chef code that ingest attributes and piggy backing on the existing attribute precedence system.

Methods involving the setting of attributes are wrapped using class_eval to intercept the attribute and check if it's the one we're looking for. If it finds the one we're looking for it sets a new attribute 'attribute_debug_location' to the value of where it was being set from to the best of it's knowledge. Since the setting of the new attribuete happens at the same precedence level it's safe to do this over and over again. This way the location will match up with the one that it actually evaluated to.

What it isn't

a knife plugin, chef handler, etc.

How to use it

• add the contents of client.rb in this repository to the top of a hosts client.rb.
• edit the 'attribut to debug' line at the top to reflect the attribute you want to determine the source of.
• run chef on the host

sudo chef-client --once

• use knife to show the value of attribute_debug_location

knife node show HOSTNAME_HERE -a attribute_debug_location

Running tests

requirements: docker, kitchen, maybe some kitchen docker plugin

kitchen test

the tests are setup like an onion, where each consecutive test case sets the test attribute at the next highest level of precedence.

Test status

Instance                                         Last Action
1-default-in-attribute-file-ubuntu-1204          Verified
2-default-in-recipe-ubuntu-1204                  Verified
3-environment-default-ubuntu-1204                Verified
4-default-in-role-ubuntu-1204                    Verified
5-force-default-in-attribute-file-ubuntu-1204    Verified
6-force-default-in-recipe-ubuntu-1204            Verified
7-normal-in-attribute-file-ubuntu-1204           Verified
8-normal-in-recipe-ubuntu-1204                   Verified
9-override-in-attribute-file-ubuntu-1204         Verified
10-override-in-recipe-ubuntu-1204                Verified
11-override-in-role-ubuntu-1204                  Verified
12-ovverride-in-environment-ubuntu-1204          Verified
13-force-override-in-attribute-file-ubuntu-1204  Verified
14-force-override-in-recipe-ubuntu-1204          Verified

each test case number corresponds to a precedence level as described here.

TODO

• Currently not checking for level 15 - "An automatic attribute identified by Ohai at the start of the chef-client run"
• other versions of chef ie 12.