A client of mine recently had a need to discover that state of a particular package from inside a fact. Ironically, someone else in the puppet-community had a similar need and was asking questions about this. So I thought it would be a good idea to blog about how to query the system agnostically without shelling out in a fact.

The original solution for many of us was to create a fact like the following:

# BTW, if you don't use `Facter::Core::Execution.execute` to run exec commands
# start using this ruby call.  It provides many more enhancements like newline 
# removal, timeouts and default values. 

# lib/facter/is_ntp_installed.rb
Facter.add(:is_ntp_installed) do
  confine :osfamily => 'RedHat'
  setcode do
     # if the returned value is empty, ntp is not installed
     ! Facter::Core::Execution.execute('rpm -qa ntp').empty?
  end
end

However, this leads us to a fact that only works on systems with rpm. If this is all you want then no need to implement anything else. Just remember to confine the fact to only RedHat based systems.

But if this module is expected to work on many operating systems you need an abstraction layer on top to find if ntp is present. Otherwise you end up writing a huge case statement that queries the system differently for each OS.

# lib/facter/is_ntp_installed.rb
require 'puppet'
Facter.add(:is_ntp_installed) do
	setcode do
		case $osfamily
		when 'redhat'
		  ! Facter::Core::Execution.execute('rpm -qa ntp').empty?
		when 'debian'
		  ! Facter::Core::Execution.execute('dpkg -l ntp').empty?
		else
			nil
		end
	end
end

The puppet RAL (Resource abstraction layer).

The RAL determines how to discover the ntp package using the type and provider mechanisms built into puppet. We utilize puppet to create a fact to use in puppet code. Genius, right? So the RAL will query the system for the name of the type we are interested in with very little work.

When we look at the output using puppet resource we see we have a ruby object with useful data. Note that the name package in package/ntp is the puppet type and ntp is the name of the resource.

package_resource = Puppet::Resource.indirection.find('package/ntp')
# Output of using the RAL
=> Package[ntp]
	{
		:name=>"ntp", 
		:ensure=>:purged, 
		:provider=>:yum, 
		:audit=>[:ensure, :package_settings], 
		:configfiles=>:keep, 
		:allow_virtual=>true, 
		:reinstall_on_refresh=>:false, 
		:loglevel=>:notice
	}

When used inside facter it looks like:

# lib/facter/is_ntp_installed.rb
require 'puppet'
Facter.add(:is_ntp_installed) do
	setcode do
		package_resource = Puppet::Resource.indirection.find('package/ntp')
	  package_resource[:ensure] != :purged || package_resource[:absent]
	end
end

This fact will call out to puppet and ask what packages have the ntp as the name. What you get back is a package resource with a few attributes that can be further filtered. You might have noticed that we never shelled out or specified rpm/deb/yum or any package provide to determine if ntp is installed.

You can use any native puppet type that is able to list out the resource. Some examples:

• user
• group
• service
• package
• firewall
• many more native and third party

Examples:

• user_resource = Puppet::Resource.indirection.find('user/apache')
• firewall_resources = Puppet::Resource.indirection.find('firewall')

So next time you need to test for a package try the Puppet RAL instead to make your code OS agnostic.