[chef] Re: Odd node.default behavior

[Daniel DeLeo < >]

On Tuesday, August 12, 2014 at 12:32 PM, John Warren wrote:

> In a test recipe I’m trying to determine whether a node attribute was 
> explicitly set and I’m seeing some odd behavior. Here is the code:
>  
>  
> log "Resolved value before: #{node['mysql']['server_root_password']}"
> log "Default value: #{node.default['mysql']['server_root_password']}"
> log "Normal value: #{node.normal['mysql']['server_root_password']}"
> log "Resolved value after: #{node['mysql']['server_root_password']}"
>  
> Here is the relevant log output:
>  
> [2014-08-12T19:19:15+00:00] INFO: Resolved value before: 
> ilikerandompasswords
> [2014-08-12T19:19:15+00:00] INFO: Default value: ilikerandompasswords
> [2014-08-12T19:19:15+00:00] INFO: Normal value: {}
> [2014-08-12T19:19:15+00:00] INFO: Resolved value after: {}
>  
> Note that the attribute value was not explicitly set and the “default” 
> value is “ilikerandompasswords”.
>  
> It looks like the “default” node value for the attribute is overridden 
> after reading the “normal” node value for the purposes of logging.
>  
> Note that I get the same behavior if I simply assign the “normal” value to 
> a variable (and don’t log it), i.e.:
>  
> val = node.normal['mysql']['server_root_password']
>  
> Is this behavior expected?
>  
> Thanks,
>  
> John

Yes, this is expected. It’s a trade-off of supporting “auto-vivification” of 
attributes. For example:

h = Hash.new
h[“foo”][“bar”] = “baz”

Is not valid in Ruby, you’d have to do:

h = Hash.new
h[“foo”] = Hash.new



h[“foo”][“bar”] = “baz”


Which is annoying.

So the way attributes work is that when you reference a specific precedence 
level, it’s assumed that you intend to set a new value, and unknown keys are 
set to new, empty Hash-like objects. (Code is here: 
https://github.com/opscode/chef/blob/ec0a273404b6485e134798fa417b678d496a6d8f/lib/chef/node/attribute_collections.rb#L92)

To peek at the values of attributes among the different precedence levels, 
use `node.debug_value()`, which is here: 
https://github.com/opscode/chef/blob/ec0a273404b6485e134798fa417b678d496a6d8f/lib/chef/node/attribute.rb#L212-238

HTH,

--  
Daniel DeLeo