Example of how to use Puppet, iteration and functions to figure out what to look up from hiera, look it up and then collect the results in a file

fun_with_functions.pp

# big parameters for testcase purposes - normally default to empty hash and lookup from hiera
class profiles::myapp(
  Hash $packages = {
    "vb" => {
      description => "the best beer in australia",
    },
    "oldgnarlyhen" => {
      description => "for hipsters",
    }
  }, 
  Array[String] $hives = ["app","db","kms","cea","lbs"],
  String $config_base = "myapp",
) {
    # install required component packages
    $json_hash = $packages.map |$key, $opts| {
      file { "/installed_${key}":
        ensure => present,
      };


      exec { "/bin/cat /tmp/data.json >  /tmp/data.json.${key}":
        require => File['/tmp/data.json'],
      };

      # must be last!
      $hives.map |$hive| {
	# interpolate the key to lookup in hiera eg `myapp::widget::app_settings`
	$lookup_key = "${config_base}::${key}::${hive}_settings";
	{$lookup_key => lookup($lookup_key)}
      }

  }.reduce |$memo, $x| {
    # collect all the arrays and make a hash
    $memo + $x
  }


  file{"/tmp/data.json":
    ensure  => present,
    content => to_json_pretty($json_hash),
  }
}


Results in:
[root@agent /]# puppet apply /shared/testa.pp 
Notice: Compiled catalog for agent.localdomain in environment production in 0.13 seconds
Notice: /Stage[main]/Profiles::Myapp/File[/tmp/data.json]/ensure: defined content as '{md5}eb6fc42f8be0360e1fe2c41da0c1b3b7'
Notice: /Stage[main]/Profiles::Myapp/Exec[/bin/cat /tmp/data.json >  /tmp/data.json.vb]/returns: executed successfully
Notice: /Stage[main]/Profiles::Myapp/Exec[/bin/cat /tmp/data.json >  /tmp/data.json.oldgnarlyhen]/returns: executed successfully
Notice: Applied catalog in 0.05 seconds