def _make_tags(ev):
    """Build statsd metric tags from CADF event."""
    return [
        'project_id:{0}'.format(ev.target.project_id or
                                ev.initiator.project_id or
                                ev.initiator.domain_id),
        'target_type_uri:{0}'.format(ev.target.typeURI),
        'action:{0}'.format(ev.action),
        'outcome:{0}'.format(ev.outcome)]