Attribute precedence in chef cookbook

Question

I am trying to implement a wrapper cookbook by taking inspiration from How to Write Reusable Chef Cookbooks, Gangnam Style. I wish to install tomcat 7 on my node without manager app. I have created a wrapper cookbook with the following attributes/default.rb file:

default["tomcat"]["base_version"] = 7
default["tomcat"]["deploy_manager_apps"] = false

The default attributes provided in tomcat/attributes/default.rb are:

default["tomcat"]["base_version"] = 6
#other attributes
default["tomcat"]["deploy_manager_apps"] = true
default["tomcat"]["user"] = "tomcat#{node["tomcat"]["base_version"]}

I wish to override these values across all attributes. However attributes such as ["tomcat"]["user"] are not getting overriden. The above still has the value of tomcat6 in node["tomcat"]["user"].

Do I have to override all the attributes which refer to ["tomcat"]["base_version"]}"? If my attributes/default.rb were loaded before tomcat cookbook's default.rb this would have worked fine.

I am using Berkshelf, Vagrant and Chef solo for development. In metadata.rb of my cookbook, I have mentioned depends "tomcat".

My custom cookbook is located at https://github.com/vaibhavguptaIITD/hcentive-ops/tree/master/hc-tomcat and tomcat community cookbook is located at https://github.com/opscode-cookbooks/tomcat.

Answer 1

This is due to how/when ruby code is evaluated during a Chef run. In a typical Chef run, the attribute files are evaluated first, in the dependency order dictated by the run_list as mentioned here: Chef 11 In-Depth: Attributes Changes.

Chef detects the dependency on the tomcat cookbook and loads/evaluates it's attributes first. So default["tomcat"]["user"] = "tomcat#{node["tomcat"]["base_version"]} is set to tomcat6 because at the time, the value of node["tomcat"]["base_version"] is 6.

Later, Chef evaluates your wrapper cookbook and properly sets the node["tomcat"]["base_version"] attribute to 7, however node["tomcat"]["user"] is never reevaluated.

So you will need to set the value for node["tomcat"]["user"] in your wrapper cookbook if you would like to change it's value.