== site.pp ==

$extlookup_datadir = "/etc/puppet/extdata"
$extlookup_precedence = ["%{fqdn}", "domain_%{domain}", "common"]

import "classes/*"
import "os/*"

== classes/manifests/apache.pp ==
$ldapserver=extlookup("ldapserver")

== extdata/domain_mydomain.csv ==
ldapserver,ldap.mydomain.com

puppet run gives :

err: Could not retrieve catalog: No match found for 'ldapserver' in any data file during extlookup() at /etc/puppet/manifests/classes/apache.pp:10 on node XXXX
warning: Not using cache on failed catalog