interpolation.tf

resource "aws_route53_record" "domain-com_A_consul-domain-com" {
  zone_id = "${var.domain_zone_id}"
  type = "A"
  name = "consul"
  ttl = "1"
  records = ["${aws_instance.host.0.public_ip}", "${aws_instance.host.1.public_ip}", "${aws_instance.host.2.public_ip}"]
}

// or

resource "aws_route53_record" "domain-com_A_consul-domain-com" {
  count = "${var.cluster_size}"
  zone_id = "${var.domain_zone_id}"
  type = "A"
  name = "consul"
  ttl = "1"
  records = ["${concat("aws_instance.api.", count.index, ".public_ip")}"]
}