Terraform AWS: override root device size using aws_launch_template and block_device_mappings

Question

I dont find a way to override root size device using block_device_mappings in aws_launch_template with terraform aws.

I know I can specify an extra volume size doing for example:

block_device_mappings {
        device_name = "/dev/xvda"
        ebs {
        volume_size = "${var.frontend_kong_volume_size}"
        volume_type = "${var.frontend_kong_volume_type}"
        delete_on_termination = "true"
        }
    }

but I get a new disk in the VM with those specifications. But what I want to do is resize the root disk.

Can you help me to figure out how to do it?

Thanks.

Answer 1

block_device_mappings is for additional block devices.

You have to know device where root device mounted. for example for centos 7 AMI it's /dev/sda1

resource "aws_launch_template" "foobar" {
  name_prefix   = "foobar"
  image_id      = "ami-9887c6e7"
  instance_type = "t2.micro"
  block_device_mappings {
    device_name = "/dev/sda1"

    ebs {
      volume_size = 40
    }
  }
}

resource "aws_autoscaling_group" "bar" {
  availability_zones = ["us-east-1a"]
  desired_capacity   = 1
  max_size           = 1
  min_size           = 1

  launch_template = {
    id      = "${aws_launch_template.foobar.id}"
    version = "$$Latest"
  }
}

But remember that update of volume size in terraform will not take effect to running instances. So you will have to replace instances to increase volume size.