Terraform (provider AWS) - Auto Scaling group doesn't take effect on a launch template change

Question

Unable to make launch template work with ASGs while using launch templates, it works with Launch Configuration using a small hack i.e by interpolating the launch configuration name in ASG resource but it doesn't work with launch templates.
ASG uses the latest version to launch new instances but doesn't change anything w.r.t to pre-running instances inspite of a change in launch template.

I understand that this is sort of expected but do we have any workaround to make launch templates work with ASG or we need to stick to launch configuration itself?

TF code snippet -

resource "aws_launch_template" "lc_ec2" {
  image_id = "${var.ami_id}"
  instance_type = "${var.app_instance_type}"
  key_name = "${var.orgname}_${var.environ}_kp"
  vpc_security_group_ids = ["${aws_security_group.sg_ec2.id}"]
  user_data = "${base64encode(var.userdata)}"
  block_device_mappings {
    device_name = "/dev/xvdv"
    ebs {
      volume_size = 15
    }
  }
  iam_instance_profile {
    name = "${var.orgname}_${var.environ}_profile"
  }
  lifecycle {
    create_before_destroy = true
  }

  tag_specifications {
    resource_type = "instance"
    tags = "${merge(map("Name", format("%s-%s-lc-ec2", var.orgname, var.environ)), var.tags)}"
    } 
  tag_specifications {
    resource_type = "volume"
   tags = "${merge(map("Name", format("%s-%s-lc-ec2-volume", var.orgname, var.environ)), var.tags)}"
    }
  tags = "${merge(map("Name", format("%s-%s-lc-ec2", var.orgname, var.environ)), var.tags)}"
}

resource "aws_autoscaling_group" "asg_ec2" {
    name = "${var.orgname}-${var.environ}-asg-ec2-${aws_launch_template.lc_ec2.name}"

    vpc_zone_identifier = ["${data.aws_subnet.private.*.id}"]
    min_size  = 1
    desired_capacity  = 1
    max_size  = 1
    target_group_arns = ["${aws_lb_target_group.alb_tg.arn}"]
    default_cooldown= 100
    health_check_grace_period = 100
    termination_policies = ["ClosestToNextInstanceHour", "NewestInstance"]
    health_check_type="ELB"
    launch_template = {
      id = "${aws_launch_template.lc_ec2.id}"
      version = "$$Latest"
   }  
      lifecycle {
    create_before_destroy = true
  }

  tags = [
    {
      key                 = "Name"
      value               = "${var.orgname}"
      propagate_at_launch = true
    },
    {
      key                 = "Environ"
      value               = "${var.environ}"
      propagate_at_launch = true
    }
  ]
}

Answer 1

There is one hack to achieve this.

AWS CloudFormation supports rolling updates of an Autoscaling group. Since Terraform supports a cloudformation stack resource, you can define your ASG as a cloudformation stack with an update policy. However, CloudFormation does not support the $$Latest tag for launch template version, so you will have to parameterize the version and take the input value from the latest_version attribute of the launch template resource created in your terraform configuration file.