Use external nodes to define puppet resources

A technique I like to use when making my puppet modules is to split out the data from the logic. This allows me to create site generic modules that work anywhere. This also allows me to change configurations on the fly without having to go through a dev/test/prod cycle with my puppet code. Extending on that, I often create virtual resources outside of my modules and then realize those resources in the classes. This way I can add/remove/modify resources per site and it 'just works.' For example, one manufacturing site might employ 5 lifters that are controlled by a server that is then managed by puppet. Another site might only have 2. Futhermore, if a new lifter is added to the second site, you don't want to have to modify your puppet classes.

To do this, I would do something like this:

site.pp:

import "resources/*.pp"

Then I would have a resource file named lifters.pp:



Then in my lifter class, I just do:

Lifter<||>

This works, but as you can imagine it gets ugly. What would be nicer is to be able to manage these in an external nodes classifer such as puppet-dashboard. Luckily with puppet 2.6, we can. We're going to make use of puppet's new pure ruby manifests. The class is going to take all the variables in puppet, including ones created by external nodes, find ones that are both hashes and have a key called :type, and turn those in to resources.

First we need to make a module called externalresources. In the manifests directory, we're going to create a init.rb file instead of a init.pp file. It's important that the init.pp file does not exist. In the init.rb file, we're going to put the following code:



In your site.pp file add this line:

include externalresources

Now we can define parameters in puppet-dashboard and have their values be hashes that look almost like puppet resources. The only difference is we're going to use symbols and we have to add a parameter called :type. Let's create a file resource.

In puppet-dashboard, create a parameter on a host you manage with the dashboard. Name the parameter the title of the file resource. For our example, /tmp/test. For the value, we'll create a hash that looks like this:

{ :type => 'file', :content => "My file's content", :ensure => 'present' }

Now when we run puppet on that host, the file /tmp/test will be created with the content My file's content. For extra fun, we can add the parameter :virtual => 'true' and externalresources will make it a virtual resource that can be realized in other classes.