DevOps: Puppet, Docker, and Kubernetes

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 whether 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. Create the directory modules/facts/lib/facter and then create the file modules/facts/lib/facter/hello.rb with the following contents:

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

2. Modify your site.pp file as follows:

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

3. Run Puppet:

   [root@cookbook ~]# puppet agent -t
   Notice: /File[/var/lib/puppet/lib/facter/hello.rb]/ensure: ...