Using libraries

You can use arbitrary Ruby code within your recipes. If your logic isn't too complicated, it's totally fine to keep it inside your recipe. However, as soon as you start using plain Ruby more than Chef DSL, it's time to the move the logic into external libraries.

Libraries provide a place to encapsulate Ruby code so that your recipes stay clean and neat. In this section, we'll create a simple library to see how this works.

Getting ready

Make sure you have a cookbook called my_cookbook and that the run_list of your node includes my_cookbook, as described in the Creating and using cookbooks recipe of Chapter 1, Chef Infrastructure.

How to do it...

Let's create a library and use it in a cookbook:

1. Create a helper method in your own cookbook's library:

   mma@laptop:~/chef-repo $ mkdir -p cookbooks/my_cookbook/libraries
   mma@laptop:~/chef-repo $ subl cookbooks/my_cookbook/libraries/ipaddress.rb
   class Chef::Recipe
     def netmask(ipaddress)
       IPAddress(ipaddress).netmask
     end
   end
   

2. Use your...