Amazon web services – Terraform launch template creating two volumes for AWS EKS Cluster Autoscaling Group

I have a EKS Cluster with a Node Group that is configured with launch template. All of the resources are created with Terraform.

launch_template.tf;

resource "aws_launch_template" "launch-template" {
  name                   = var.name
  update_default_version = var.update_default_version

  instance_type = var.instance_type

  key_name = var.key_name

  block_device_mappings {
    device_name = var.block_device_name

    ebs {
      volume_size = var.volume_size
    }
  }

  ebs_optimized = var.ebs_optimized

  monitoring {
    enabled = var.monitoring_enabled
  }

  dynamic "tag_specifications" {
    for_each = toset(var.resources_to_tag)
    content {
       resource_type = tag_specifications.key
       tags = var.tags
    }
  }
}

eks_nodegroup.tf;

resource "aws_eks_node_group" "eks-nodegroup" {
  cluster_name    = var.cluster_name
  node_group_name = var.node_group_name
  node_role_arn  = var.node_role_arn
  subnet_ids     = var.subnet_ids

  labels = var.labels

  tags = var.tags

  scaling_config {
    desired_size = var.desired_size
    max_size     = var.max_size
    min_size     = var.min_size
  }

  launch_template {
    id        = var.launch_template_id
    version   = var.launch_template_version
  }
}

These resources are binding each other. But at the end of the day,
this setup is creating

• 2 launch templates,
• 1 autoscaling group
• 2 volumes for each instance in autoscaling group.

I understood from this question that, because I’m using aws_launch_template resource with aws_eks_node_group; second launch template is being created. But I didn’t understand where the second volume is coming from for each instance. One of the volumes fits my configuration which has 40 GB capacity, path is /dev/sda1 and IOPS is 120. But the second one has 20 GB capacity, path is /dev/xvda and IOPS is 100. I don’t have any configuration like this in my Terraform structure.

I didn’t find where is the source of the second volume. Any guidance will be highly appreciated, Thank you very much.