def elbv2_target_group_arn_suffix(self, lookup, default=None):
    """
    Args:
      lookup: the friendly name of the v2 elb target group
      default: value to return in case of no match
    Returns:
      The shorthand fragment of the target group's ARN, of the form
      `targetgroup/*/*`
    """
    try:
      client = EFAwsResolver.__CLIENTS['elbv2']
      elbs = client.describe_target_groups(Names=[lookup])
      elb = elbs['TargetGroups'][0]
      m = re.search(r'.+?(targetgroup\/[^\/]+\/[^\/]+)$', elb['TargetGroupArn'])
      return m.group(1)
    except ClientError:
      return default