Writing Custom Puppet Facts

1. Move into the nginx module directory:

   cd /etc/puppetlabs/code/environments/production/modules/nginx/
   

2. Create the plugin library location for Facter:

   sudo mkdir -p lib/facter
   

3. Create and open a file called web.rb in the plugin location:

   sudo vim lib/facter/web.rb
   

4. At its most basic, if we wanted to write a single, non-structured fact that output our web server information, we could write something like:

   Facter.add(:web) do
     setcode do
       'Nginx'
     end
   end
   

   Notice how this includes the Facter.add line to set our fact name, and the setcode statement, which provides us our output. Since we just want to supply the text Nginx, that is all we put in our statement block.

5. However, since we need this to become a structured, aggregate fact, we're going to refactor this so we can add more facts to our code. Let's first define the overall web fact as an aggregate, which means the resolution of our web fact can be read in separate chunks:

   Facter.add(:web, :type => :aggregate) do
   

6. Next, we want to replace our setcode statement with chunk, which lets us define the different parts of our structured fact:

   Facter.add(:web, :type => :aggregate) do
     chunk(:server) do
   

7. We now need to update the structure of our output, so it resembles the JSON output we expected when we query for facts. To this, let's create a variable, web, then add our Nginx value as a structured key-value pair:

   Facter.add(:web, :type => :aggregate) do
     chunk(:server) do
       web = {:server => 'Nginx'}
       web
     end
   end
   

   Save and exit.

8. Let's now test our fact:

   sudo puppet agent -t
   sudo facter -p web
   sudo facter -p web.server
   

1. Back in the lib/facter/web.rb file, create a second chunk line, this one called version; include a line at the end calling the web variable:

     chunk(:version) do
       web
     end
   

2. We're going to check our version by using a slightly edited version of the nginx -v command — which means we need nginx for this fact to work. Let's add an if statement checking for nginx:

     chunk(:version) do
       if Facter::Core::Execution.which('nginx') != nil
       end
       web
     end
   

3. Finally, we want to execute the appropriate command and have the output sent to a structured line mapped to web. Because our command is on the long side, you may want to create a variable for its output:

     chunk(:version) do
       if Facter::Core::Execution.which('nginx') != nil
         version = Facter::Core::Execution.execute('nginx -v 2>&1 | grep -Po [0-9]+\.[0-9]+\.[0-9]+')
         web = {:version => version}
       end
       web
     end
   

4. If desired, save and test your code thus far.

Mimic the same structures as the previous chunks to create the stanza that provides the amount of running processes:

  chunk(:processes) do
   processes = Facter::Core::Execution.execute('pgrep nginx | wc -l')
   web = {:processes => processes }
   web
  end

The full file should look like:

Facter.add(:web, :type => :aggregate) do
  chunk(:server) do
   web = {:server => 'Nginx'}
   web
  end

  chunk(:version) do
   if Facter::Core::Execution.which('nginx') != nil
     version = Facter::Core::Execution.execute('nginx -v 2>&1 | grep -Po [0-9]+\.[0-9]+\.[0-9]+')
     web = {:version => version}
   end
   web
  end

  chunk(:processes) do
   processes = Facter::Core::Execution.execute('pgrep nginx | wc -l')
   web = {:processes => processes }
   web
  end
end

Test that each fact works, as well as the overall web fact. Note that the second server is provided so you can test on a node with Nginx, as well as one without it (remember, our Puppet master does not have Nginx installed):

sudo puppet agent -t
sudo facter -p web
sudo facter -p web.server
sudo facter -p web.version
sudo facter -p web.processes