如何使用 Terraform 获取新创建的实例 ID

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.