How to dynamically tag instance via a module in Terraform?

tagging_instances.tf

variable "ami_id" { }
variable "subnet_id" { }
variable "security_group_id" { }
variable "key_name" { }
variable "instance_profile" { }
variable "instance_type" { }
variable "instance_name" { }
variable "hostname" { }
variable "tag_role" { }
variable "tag_cost_environment" { }
variable "tag_critical" { }
variable "tag_environment" { }
variable "tag_extra_one" { }
variable "tag_extra_two" { }
variable "tag_extra_three" { }


resource "template_file" "user_data" {
    template = "${file("${path.module}/../../_utilities/bootstrap.sh")}"

    vars {
        hostname = "${var.hostname}"
    }
}


resource "aws_instance" "instance" {
    instance_type = "${var.instance_type}"
    iam_instance_profile = "${var.instance_profile}"
    ami = "${var.ami_id}"
    key_name = "${var.key_name}"
    vpc_security_group_ids = ["${var.security_group_id}"]
    subnet_id = "${var.subnet_id}"

    tags {
        Name = "${var.instance_name}"
        Roles = "${var.tag_role}"
        Environment = "${var.tag_environment}"
        CostEnvironment = "${var.tag_cost_environment}"
        Critical = "${var.tag_critical}"
        # How to do additional tags?
    }
}

Did you find any way to do that?