[Puppet Users] Using regex to match hostnames in hiera

Hi, I'm having a problem with extlookup not respecting the 'certname' parameter[1].  When executing a puppet run with either the --certname or --fqdn parameters, it ends up using the specified SSL certificate and gets the correct node definition applied from the puppetmaster.  However, it still retrieves extlookup data using the node's actual FQDN, not the one manually specified using the parameter.

Anyway, I thought this might be a bug in the extlookup code so I decided to try out hiera as an alternative.  It seems like a nice tool, but in my case there is a very big downside - the inability to match the fqdn based on a regular expression.  This was brought up in a previous thread[2].

As an example, here is my existing extlookup configuration from site.pp:

$hostgroup = regsubst($hostname, '-*\d+$', '')
$extlookup_datadir = "/etc/puppet/environments/${environment}/manifests/extdata"
$extlookup_precedence = [ 'hostnames/%{fqdn}', 'hostgroups/%{hostgroup}', 'common' ]

This layout is quite beautiful, as it has three possible matching scenarios.

1. A CSV file for a specific hostname exists.  Example: hostnames/web1.mydomain.com.csv applies to a single host - web1.mydomain.com.
2. A CSV file for a regular expression based on hostname exists.  Example: hostgroups/web.csv applies to all hosts whose hostname begins with 'web' - web1.mydomain.com or web999.mydomain.com.
3. No matches are found, so default values from common.csv are used.

I'd like to replicate this behavior using hiera.  Is it possible?

P.S.  The first reply to the aforementioned mailing list thread suggested creating a custom fact and using that to specify the node's hostgroup.  Please don't recommend that!  To begin with, such measures aren't necessary with extlookup.  Hiera is the shiny/new/better successor to extlookup, I shouldn't have to create a custom fact to reproduce the old functionality.  Secondly, I have another good reason but it is complicated and would take too long to explain.  Just take my word for it :-)

Thank you.

[1] https://projects.puppetlabs.com/issues/17198
[2] https://groups.google.com/forum/?fromgroups=#!topic/puppet-users/aGFSQ2SYgL8