I can't figure out how to associate my EC2 instances with an auto scaling group-CodePudding

I've never implemented an ASG before, so I thought I could create an instance and an ASG w/ a launch template like-so:

resource "aws_instance" "bastion" {
  count           = var.azs
  ami             = data.aws_ami.AL2_ami.id
  key_name        = aws_key_pair.bastion_auth.id
  instance_type   = var.instance_type
  security_groups = [aws_security_group.bastion-sg.id]

  associate_public_ip_address = true
  subnet_id                   = module.vpc.public_subnets[count.index]
  user_data                   = file("userdata.tpl")

  root_block_device {
    volume_size = var.main_vol_size
  }

  tags = {
    Name = "${var.name}-bastion-host-${count.index   1}"
  }
}

resource "aws_launch_template" "bastion_launch_template" {
  name_prefix   = "bastion-launch-template"
  image_id      = data.aws_ami.AL2_ami.id
  instance_type = var.instance_type
  key_name      = aws_key_pair.bastion_auth.id
  tags = {
    Name = "${var.name}-bastion-launch-template"
  }
}

resource "aws_placement_group" "bastion_placement_group" {
  name     = "bastion-placement-group"
  strategy = "spread"
  tags = {
    Name = "${var.name}-bastion-placement-group"
  }
}

resource "aws_autoscaling_group" "bastion_asg" {
  name                      = "bastion-asg"
  max_size                  = 3
  min_size                  = 3
  health_check_grace_period = 60
  health_check_type         = "EC2"
  placement_group           = aws_placement_group.bastion_placement_group.id
  availability_zones        = module.vpc.azs

  launch_template {
    id      = aws_launch_template.bastion_launch_template.id
    version = "$Default"
  }
}

It's a bastion host so I also have a security group to allow only SSH, but all this did was create 3 bastion hosts (like I wanted) and then 3 separate instances because of the auto-scaling group. I tried looking into using an auto scaling group attachment but based off the docs, I can only use it to attach to load balancers?

My goal is to have 3 instances that act as a bastion host and are attached to an ASG. Do I completely omit the aws_instance resource block and deploy the instances through the ASG launch template? Or is there a way to associate the ASG with my instances that get deployed with the aws_instance resource block

CodePudding user response：

You don't need a separate aws_instance resource. ASG will take care of creating instances from the launch-template itself.

  resource "aws_launch_template" "bastion_launch_template" {
  name_prefix   = "bastion-launch-template"
  image_id      = data.aws_ami.AL2_ami.id
  instance_type = var.instance_type
  key_name      = aws_key_pair.bastion_auth.id
  tags = {
    Name = "${var.name}-bastion-launch-template"
  }
}

resource "aws_placement_group" "bastion_placement_group" {
  name     = "bastion-placement-group"
  strategy = "spread"
  tags = {
    Name = "${var.name}-bastion-placement-group"
  }
}

resource "aws_autoscaling_group" "bastion_asg" {
  name                      = "bastion-asg"
  max_size                  = 3
  min_size                  = 3
  health_check_grace_period = 60
  health_check_type         = "EC2"
  placement_group           = aws_placement_group.bastion_placement_group.id
  availability_zones        = module.vpc.azs

  launch_template {
    id      = aws_launch_template.bastion_launch_template.id
    version = "$Default"
  }
}