def elbv2_load_balancer_arn_suffix(self, lookup, default=None):
    """
    Args:
      lookup: the friendly name of the v2 elb to look up
      default: value to return in case of no match
    Returns:
      The shorthand fragment of the ALB's ARN, of the form `app/*/*`
    """
    try:
      elb = self._elbv2_load_balancer(lookup)
      m = re.search(r'.+?(app\/[^\/]+\/[^\/]+)$', elb['LoadBalancerArn'])
      return m.group(1)
    except ClientError:
      return default