iam.tf

variable "role_name" {}
variable "role_policy_file" {}

resource "aws_iam_role" "role" {
  name               = "${var.role_name}"
  assume_role_policy = "${file("${path.module}/policies/${var.role_policy_file}")}"
}

output "role_arn" {
  value = "${aws_iam_role.role.arn}"
}

main.tf

/*
 * Directory structure
 *  .
 *  ├── main.tf
 *  ├── modules
 *  │   └── iam_role
 *  │       ├── iam.tf
 *  │       └── policies
 *  │           ├── differentname_policy.json
 *  │           └── exampleroles_policy.json
 */

module "role_exampleroles" {
  source           = "./modules/iam_role"
  role_name        = "exampleroles"
  role_policy_file = "exampleroles_policy.json"
}

module "role_differentname" {
  source           = "./modules/iam_role"
  role_name        = "differentname"
  role_policy_file = "differentname_policy.json"
}

output "role_exampleroles_arn" {
  value = "${module.role_exampleroles.role_arn}"
}

output "role_differentname_arn" {
  value = "${module.role_differentname.role_arn}"
}