Can you access node attributes from within a Chef custom resource definition?

Chef Infra (archive)
1

Can you access node attributes from within a Chef custom resource definition?

E.g., is this allowed:

action :run do
  if node['foo']
    <do_stuff> 
  end
end

My resource that does that appears to always be evaluating node['foo'] to “false,” making me wonder if the node object is even accessible within the resource definition.

The Chef.io page Custom Resources doesn’t show any examples of referring to a node attribute in the manner shown above. It does show references to a construct node.run_state['foo'], but I’m not clear on whether that’s the syntax we are supposed to use to reference node attributes from with a custom resource definition.

Thank you!

2

So the intent is if there is a variable necessary in your custom resource, you should pass it through as a resource property. The goal being that the one and only way to control your resource is through its properties, not via node attributes.

In short, instead of using node['foo'] directly, pass foo in through a resource property and reference the new_resource value.

3

Thanks for your fast response, Tom. Now I know:

You cannot access node attributes from within a Chef custom resource definition. If your custom resource needs access to variable values, you must pass them in as resource properties.

I appreciate your help!

4

You can do it, it just isn’t recommended. It mostly comes up for using the value of an attribute as the default value for a property, which isn’t the worst thing in the world sometimes. For that just use a lazy definition: property(:foo, default: lazy { node["whatever"] })

Original Quoted context has been removed as per policy

5

Ah! Thanks, Noah. My new understanding is:

You can access node attributes from within a Chef custom resource definition -- but you shouldn't! It's not recommended. If your custom resource needs access to variable values, you should pass them in as resource properties.