title: Add ASG instances in target group via Terraform
body: <p>I have a Terraform script which creates a launch config, autoscaling group, a single ALB, one target group and a listener. The instances are launched using the autoscaling group.</p>
  
  <p>How can I add the newly launched instances in target group via Terraform in the same script?</p>
  
  <pre><code>resource "aws_launch_configuration" "CF2TF-LC" {
    name                 = "CF2TF-LC"
    depends_on           = ["aws_iam_role_policy_attachment.CF2TF-IAM-PA", "aws_security_group.CF2TF-SG-Web"]
    image_id             = "ami-14c5486b"
    instance_type        = "t2.micro"
    iam_instance_profile = "${aws_iam_instance_profile.CF2TF-IAM-IP.id}"
    key_name             = "CF2TF"
    security_groups      = ["${aws_security_group.CF2TF-SG-Web.id}"]
    user_data            = "${template_file.CF2TF-UserData.rendered}"
  }
  
  resource "aws_autoscaling_group" "CF2TF-ASG" {
    name                      = "CF2TF-ASG"
    depends_on                = ["aws_launch_configuration.CF2TF-LC"]
    vpc_zone_identifier       = ["${aws_subnet.CF2TF-Subnet-1a.id}", "${aws_subnet.CF2TF-Subnet-1d.id}"]
    max_size                  = 3
    min_size                  = 2
    health_check_grace_period = 300
    health_check_type         = "EC2"
    desired_capacity          = 2
    force_delete              = true
    launch_configuration      = "${aws_launch_configuration.CF2TF-LC.id}"
  }
  
  resource "aws_lb" "CF2TF-ALB" {
    name               = "CF2TF-ALB"
    subnets            = ["${aws_subnet.CF2TF-Subnet-1a.id}", "${aws_subnet.CF2TF-Subnet-1d.id}"]
    internal           = false
    load_balancer_type = "application"
    security_groups    = ["${aws_security_group.CF2TF-SG-Web.id}"]
  
    tags {
      Name        = "WebSrv"
      Environment = "Dev"
    }
  }
  
  resource "aws_lb_target_group" "CF2TF-TargetGroup" {
    name        = "CF2TF-TargetGroup"
    depends_on  = ["aws_vpc.CF2TF-VPC"]
    port        = 80
    protocol    = "HTTP"
    vpc_id      = "${aws_vpc.CF2TF-VPC.id}"
    target_type = "instance"
  
    health_check {
      interval            = 30
      path                = "/index.html"
      port                = 80
      healthy_threshold   = 5
      unhealthy_threshold = 2
      timeout             = 5
      protocol            = "HTTP"
      matcher             = "200,202"
    }
  }
  
  resource "aws_lb_listener" "CF2TF-ALB-Listener" {
    //depends_on = ["aws_lb.CF2TF-ALB.id", "aws_lb_target_group.CF2TF-TargetGroup.id"]
    load_balancer_arn = "${aws_lb.CF2TF-ALB.arn}"
    port              = "80"
    protocol          = "HTTP"
  
    default_action {
      target_group_arn = "${aws_lb_target_group.CF2TF-TargetGroup.arn}"
      type             = "forward"
    }
  }
  </code></pre>