Replacement for hiera using mixlib-config and a few lines of code

puppet_attributes_function.rb

# This is a puppet function similar to the hiera() lookup function.
#
# It can load yaml, json or ruby config files
#
# It uses [mixlib-config](https://github.com/chef/mixlib-config/) so, when writing ruby config files
# you have a flexible DSL at your disposal, similar to the chef attributes DSL.
# 
# You could also use ruby any way you like inside these configuration files, including calling out 
# to external data sources.
#
# This is not more than a proof of concept.
#
require 'mixlib/config'

module Attributes
  extend Mixlib::Config
end

ATTRIBUTES_ROOT = '/tmp/layers'

Puppet::Parser::Functions::newfunction(:attribute,
                                       :type => :rvalue,
                                       :arity => 1,
                                       :doc => "Similar to a hiera() lookup call"
                                       ) do |args|

  def add_layer_if_present(layer)
    if (result = lookupvar layer)
      "#{layer}/#{result}"
    end
  end

  layers = []
  layers << "common"
  layers << add_layer_if_present('datacenter')
  layers << add_layer_if_present('cluster')
  layers << add_layer_if_present('node')
  layers.compact!

  files = layers.map do |layer|
    Dir.glob ATTRIBUTES_ROOT + "/" + layer + ".*"
  end.flatten

  files.each do |file|
    next unless File.file? file
    Attributes.from_file file
  end

  attributes = Attributes.save
  Attributes.reset

  lookup_attribute = args[0].to_sym

  attributes[lookup_attribute]
end