How to get newly created instance id using Terraform - amazon-ec2

Question

I am creating AWS ec2 instance(s) using auto scaling group and launch template. I would like to get instance ids of the newly launched instances. Is this possible?
For brevity purpose I have removed some code
resource "aws_launch_template" "service_launch_template" {
name_prefix = "${var.name_prefix}-lt"
image_id = var.ami_image_id
iam_instance_profile {
name = var.instance_profile
}
lifecycle {
create_before_destroy = true
}
}
resource "aws_lb_target_group" "service_target_group" {
name = "${var.name_prefix}-tg"
target_type = "instance"
vpc_id = var.vpc_id
lifecycle {
create_before_destroy = true
}
}
resource "aws_autoscaling_group" "service_autoscaling_group" {
name = "${var.name_prefix}-asg"
max_size = var.max_instances
min_size = var.min_instances
desired_capacity = var.desired_instances
target_group_arns = [aws_lb_target_group.service_target_group.arn]
health_check_type = "ELB"
launch_template {
id = aws_launch_template.service_launch_template.id
version = aws_launch_template.service_launch_template.latest_version
}
depends_on = [aws_alb_listener.service_frontend_https]
lifecycle {
create_before_destroy = true
}
}
resource "aws_alb" "service_frontend" {
name = "${var.name_prefix}-alb"
load_balancer_type = "application"
lifecycle {
create_before_destroy = true
}
}
resource "aws_alb_listener" "service_frontend_https" {
load_balancer_arn = aws_alb.service_frontend.arn
protocol = "HTTPS"
port = "443"
}
This is working. But I would like to output the instance ids of the newly launched instances. From terraform documentation looks like the aws_launch_template or aws_autoscaling_group does not export the instance ids. What are my options here?

Answer 1

Terraform is probably completing, and exiting, before the auto-scaling group has even triggered a scale-up event and created the instances. There's no way for Terraform to know about the individual instances, since Terraform isn't managing those instances, the auto-scaling group is managing them. You would need to use another tool, like the AWS CLI, to get the instance IDs.