https://blog.gruntwork.io/terraform-tips-tricks-loops-if-statements-and-gotchas-f739bbae55f9

gistfile1.txt

resource "aws_eip" "example" {
  count = "${var.create_eip}"
  instance = "${aws_instance.example.id}"
}
resource "aws_route53_record" "example" {
  count = "${1 - var.create_eip}"
  zone_id = "A1B2CDEF3GH4IJ"
  name = "foo.example.com"
  type = "A"
  ttl = 300
  records = ["${aws_instance.example.public_ip}"]
}