mon host = {% for host in groups[mon_group_name] %}
  {% for key in hostvars[host].iterkeys() %}
    {% if hostvars[host][key]['macaddress'] is defined and hostvars[host][key]['device'] is defined and hostvars[host][key]['device'] == monitor_interface %}
      {{ hostvars[host][key]['ipv4']['address'] }}
    {% endif %}
  {% endfor %}
{% if not loop.last %},{% endif %}{% endfor %}