So, obviously,we use puppet a great deal. One thing a few of us have wanted for a while was the ability to ssee that nodes/node groups would be affected by a change to a particular class. In other words, what hosts get $This class?

Now, nodes are aware what classes they get, but the puppet master seemingly is not, not really. It compiles teh catalog on a per-run basis, and while durring that it DOES know what classes a system gets, it doesn’t really store that info. So, a simple custom fact to pull that data in from each host:

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#list puppet classes, on per fact
require 'facter'

IO.popen('cat /var/lib/puppet/classes.txt | tail -n+3').readlines.each do |line|
        Facter.add("puppet_class_#{line}") do
                setcode do
                        "true"
                end
        end
end

So, now we get, for each host, a bunch of facts like:

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puppet_class_syslog => true 

Reported from facter -p, and therefor sent back to teh puppet master, into a DB, which we can query directly, via teh puppet api, or via Foreman.