You can use the fail
function for that. I usually do something like this:
class postfix::params {
case $::operatingsystem {
Debian, Ubuntu: {
$postfix_package_name = 'postfix'
$postfix_postmap_command = '/usr/sbin/postmap'
$postfix_service_name = 'postfix'
}
default: { fail("${::hostname}: Module ${::module_name} does not support operatingsystem ${::operatingsystem}") }
}
}
This makes the module fail on Puppet nodes that are not running Debian or Ubuntu.
Oh, and please, for the love of all that is good and holy, upgrade your Puppet installation. 0.24 is ancient and I don't think it is even supported any more. Puppetlabs provide up-to-date stable packages (see apt.puppetlabs.com), or you can use the ones from http://backports-master.debian.org/.