Variance in attributes based on count.index in terraform

Question

I\'m using Hashicorp terraform to create a MySQL cluster on AWS. I created a module named mysql and want to tag the first instance created as the master

Answer 1

The way you have count in the module resource would infer that you want 3 modules created, rather than 3 resources within the module created. You can stipulate the count from the module resource but any logic using count.index needs to sit within the module.

main.tf

module "mysql_cluster" {
  source          = "./modules/mysql"
  instance_count  = 3
}

mysql.tf

resource "aws_instance" "mysql" {
  count         = "${var.instance_count}"
  ami           = "ami-123456"
  instance_type = "t2.xlarge"
  key_name      = "rsa_2048"

  tags {
    Role        = "${count.index == "0" ? "master" : "slave"}"
  }
}