Creating custom facts

While Facter's built-in facts are useful, it's actually quite easy to add your own facts. For example, if you have machines in different data centers or hosting providers, you could add a custom fact for this so that Puppet can determine if any local settings need to be applied (for example, local DNS servers or network routes).

How to do it…

Here's an example of a simple custom fact:

1. Run the following command:

   ubuntu@cookbook:~/puppet$ mkdir -p modules/facts/lib/facter
   

2. Create the file modules/facts/lib/facter/hello.rb with the following contents:

   Facter.add(:hello) do
     setcode do
       "Hello, world"
     end
   end

3. Modify your manifests/nodes.pp file as follows:

   node 'cookbook' {
     notify { $::hello: }
   }

4. Run Puppet:

   ubuntu@cookbook:~/puppet$ papply
   Notice: Hello, world
   Notice: /Stage[main]//Node[cookbook]/Notify[Hello, world]/message: defined 'message' as 'Hello, world'
   Notice: Finished catalog run in 0.24 seconds
   

How it works...

The built-in facts in Facter are defined in the same...