gistfile1.pp

class webserver {
  concat { '/etc/apache/vhostsfile':
  }
}

define webserver::vhost($param) {
  concat::fragment { "webserver_vhost_$name":
    target => '/etc/apache/vhostsfile',
    content => template('vhost_template'),
  }
}

class internal_webserver {
  include webserver

  webserver::vhost{ 'internal.site':
    param => 'some stuff',
  }
}

class more_hosts {
  include webserver
  
  webserver::vhost{ 'another.host.1':
    param => 'different stuff',
  }
}

include internal_webserver
include more_hosts