[chef] Override attributes using JSON

[Vladimir Girnet < >]

Hi,

I'm using Chef 0.9.6 on CentOS 5.5 - everything installed from Yum
repositories.

I need to create a user in the system, and then access this username in 
several
cookbooks.  I have created a cookbook "create_user" that has this receipe:

user_name = node[:user_name]

username user_name do
 ... create actions here
end

And I have created an attribute for this cookbook:
default[:user_name]="testuser"

So, if there is no username supplied, "testuser" is used. 

Also, I'm creating a JSON file { "user_name": "myuser" }

When I run "chef-client -j <myfile>.json" on a non-registered node/client -
user "testuser" is created. Running the same command second time - node is
already registered from first run - user "myuser" is created.

If I run the same cookbook using chef-solo - everything works fine - only
"myuser" is created. 

Why on first run of chef-client attributes are not overridden?  How is 
possible
to achieve correct user creation on first chef-client run?

Thanks