Chef custom attributes

Question

I'm working on a custom Chef Cookbook and have defined a custom attribute called default["server"]["apikey"] = nil thats been defined within the cookbook in a separate attributes file that looks like this:

#Default Attributes
default["webhooks"]["get_response"] = ""
default["webhooks"]["put_response"] = ""
default["webhooks"]["post_response"] = ""

default["server"]["username"] = "user"
default["server"]["password"] = "123"

default["server"]["apikey"] = nil

Within my recipe I then do this:

webhooks_request "Request an API key from TPP " do
  uri "172.16.28.200/sdk/authorize/"
  post_data (
            { 'Username' => node["server"]["username"], 'Password' => node["server"]["password"]}
        )
  header_data (
              { 'content-type' => 'application/json'}
          )
  expected_response_codes [ 200, 201, 400 ]
  action :post
end

I then follow this with ruby_block that updates the value of the ``default["server"]["apikey"]` attribute with the API key like this:

ruby_block "Extract the API Key" do
  block do
    jsonData = JSON.parse(node["webhooks"]["post_response"])
    jsonData.each do | k, v |
      if k == 'APIKey'
        node.overide["server"]["apikey"] = v
      end
    end
  end
  action :run
end

I can then validate it using this:

ruby_block "Print API Key" do
  block do
    print "\nKey = : " + node["server"]["apikey"] + "\n"
  end
  action :run
end

However, if I then try to use the node["server"]["apikey"] attribute in a following block like this:

webhooks_request "Get data from TPP" do
  uri "127.0.0.1/vedsdk/certificates/retrieve?apikey=#{node["server"]["apikey"]}"
  post_data (
                { 'data' => "NsCVcQg4fd"}
        )
  header_data (
              { 'content-type' => 'application/json', 'auth' => node["server"] ["username"]}
              )
  expected_response_codes [ 200, 201, 400, 401 ]
  action :post
end

The value of node["server"]["apikey"]} is always empty. Interestingly though the value of the node["server"] ["username"] attribute is available and works as expected.

Obviously, I'm missing something here buy can't work out what :(

Use lazy evaluation for the attribute. The value is read at compile time but is set at converge time (inside the ruby_block). See [this answer](http://stackoverflow.com/questions/28357365/when-are-default-node-attributes-set-during-a-chef-client-run/28361825#28361825) for a more detailled explanation. (i.e your uri attribute should be: `uri "127.0.0.1/vedsdk/certificates/retrieve?apikey=#{lazy { node["server"]["apikey"] } }"` — Tensibai, Mar 06 '15 at 14:16
Thanks just tried that but that just returns a delayed evaluator e.g. — user1513388, Mar 06 '15 at 14:32
Indeed, sorry, did a little more search and foudn [this one](http://stackoverflow.com/questions/20620724/how-to-lazily-evaluate-an-arbitrary-variable-with-chef) which is precisely your case — Tensibai, Mar 06 '15 at 15:01
OMG I'm sorry, I've been totally wrong. try this one: `uri lazy {"127.0.0.1/vedsdk/certificates/retrieve?apikey=#{node["server"]["apikey"]}"}`(tested and OK for me) — Tensibai, Mar 06 '15 at 15:14
Well that worked :) thankyou very much. This seems rather obscure and god knows how I would have found it without your help. Is this how its supposed to work by design? — user1513388, Mar 06 '15 at 16:35
Yes it is designed to evaluate an attribute value at converge time. My first error was to use it inside the value instead of around the value. To be honest I did some trials and errors runs with a simple recipe with two resources (one `ruby_block` to set a value and one `log` resource to print it) before being sure of how to use it cleanly — Tensibai, Mar 06 '15 at 16:38
Great thanks again - is this documented anywhere? Seems that my use case is fairly common. — user1513388, Mar 06 '15 at 17:29
It's documentation is [here on docs.chef.io](https://docs.chef.io/resource_common.html#lazy-attribute-evaluation) — Tensibai, Mar 06 '15 at 17:30

score 2 · Accepted Answer · answered Mar 06 '15 at 17:36

Writing it as a generic answer (it will avoid keeping it unanswered in list too ;))

When inside a resource you may evaluate an attribute value at converge time with lazy attribute evaluation.

The correct usage is

resource "name" do
  attribute lazy {"any value #{with interpolation} inside"}
end

The common error is to use lazy inside interpolation as we only want the variable to be lazy evaluated and there's only one.

By design lazy is meant to evaluate the attribute value, it can contain Ruby code to compute the value from something done by a previous resource too.

Chef custom attributes

1 Answers1