Defining cookbook dependencies

Quite often, you might want to use features of other cookbooks in your own cookbooks. For example, if you want to make sure that all packages required for compiling software written in C are installed, you might want to include the build-essential cookbook, which does just that. Chef server needs to know about such dependencies in your cookbooks. You declare them in a cookbook's metadata.

Getting ready

Make sure you have a cookbook named my_cookbook, and the run_list command of your node includes my_cookbook, as described in the Creating and using cookbooks recipe in this chapter.

How to do it...

Edit the metadata of your cookbook in the file cookbooks/my_cookbook/metadata.rb to add a dependency to the build-essential cookbook:

mma@laptop:~/chef-repo $ subl cookbooks/my_cookbook/metadata.rb
...
depends 'build-essential'
depends 'apache2', '>= 1.0.4'

How it works...

If you want to use a feature of another cookbook inside your cookbook, you will need to include the other cookbook in your recipe using the include_recipe directive:

include_recipe 'build-essential'

To tell the Chef server that your cookbook requires the build-essential cookbook, you need to declare that dependency in the metadata.rb file. If you uploaded all the dependencies to your Chef server either using berks install and berks upload or knife cookbook upload ..., the Chef server will then send all the required cookbooks to the node.

Tip

The first depends call tells the Chef server that your cookbook depends on the latest version of the build-essential cookbook.

The second depends call tells the Chef server that your cookbook depends on a version of the apache2 cookbook, which is greater or equal to the version 1.0.4. You may use any of these version constraints with your depends calls:

• < (less than)
• <= (less than or equal to)
• = (equal to)
• >= (greater than or equal to)
• ~> (approximately greater than)
• > (greater than)

There's more...

If you include another recipe inside your recipe, without declaring the cookbook dependency in your metadata.rb file, Foodcritic will warn you:

mma@laptop:~/chef-repo $ foodcritic cookbooks/my_cookbook

FC007: Ensure recipe dependencies are reflected in cookbook metadata: cookbooks/my_cookbook/recipes/default.rb:9

Tip

Foodcritic will just return an empty line, if it doesn't find any issues.

Additionally, you can declare conflicting cookbooks through the conflicts call:

conflicts "nginx"

Of course, you can use version constraints exactly the way you did with depends.

See also

• Read more on how you can find out what is uploaded on your Chef server in the Inspecting files on your Chef server with knife recipe in this chapter
• Find out how to use foodcritic in the Flagging problems in your Chef cookbooks recipe in Chapter 2, Evaluating and Troubleshooting Cookbooks and Chef Runs