Adding additional instances that have volume attachments

[hashibot]

This issue was originally opened by @micahlmartin as hashicorp/terraform#8395. It was migrated here as part of the provider split. The original body of the issue is below.

---

I have a module that creates an instance or mysql and attaches an ebs volume. I'm trying to increase the number of instances from 1 to 3. Here is the configuration:

resource "aws_instance" "mysql_galera" {
  count = "${var.instances}"
  ami = "${var.ami_id}"
  instance_type = "${var.instance_type}"
  vpc_security_group_ids = ["${var.security_groups}"]
  subnet_id = "${element(var.subnets, count.index)}"
  user_data = "${data.template_cloudinit_config.config.rendered}"
  iam_instance_profile = "${var.iam_instance_profile}"
  ebs_optimized = true
  ....
}

resource "aws_ebs_volume" "mysql_galera_ebs_volume" {
  depends_on = ["aws_instance.mysql_galera"]
  count = "${var.instances}"
  availability_zone = "${element(aws_instance.mysql_galera.*.availability_zone, count.index)}"
  encrypted = "${var.ebs_encrypted}"
  size = "${var.ebs_size}"
  type = "${var.ebs_type}"
}

resource "aws_volume_attachment" "mysql_galera_ebs_attachment" {
  count = "${var.instances}"
  device_name = "/dev/sdh"
  volume_id = "${element(aws_ebs_volume.mysql_galera_ebs_volume.*.id, count.index)}"
  instance_id = "${element(aws_instance.mysql_galera.*.id, count.index)}"
}

Here's the relevant part of the plan:

-/+ module.base.mysql_galera.aws_volume_attachment.mysql_galera_ebs_attachment.0
    device_name:  "/dev/sdh" => "/dev/sdh"
    force_detach: "" => "<computed>"
    instance_id:  "i-xxx" => "${element(aws_instance.mysql_galera.*.id, count.index)}" (forces new resource)
    volume_id:    "vol-xxx" => "${element(aws_ebs_volume.mysql_galera_ebs_volume.*.id, count.index)}" (forces new resource)

If I've already created the first resource and then increase the count to 3 this is what I get. Any ideas on how to handle this?

[bflad]

I'm able to reproduce this issue on Terraform 0.11.10 with the below configuration - we can check Terraform 0.12 to see if it helps.

terraform {
  required_version = "0.11.10"
}

provider "aws" {
  region  = "us-east-1"
  version = "1.43.0"
}

variable "count" {
  # bug encountered when updated to 3
  default = 1
}

data "aws_ami" "test" {
  most_recent = true
  owners      = ["amazon"]

  filter {
    name   = "name"
    values = ["amzn-ami-hvm-*-x86_64-gp2"]
  }
}

data "aws_availability_zones" "available" {}

data "aws_subnet" "test" {
  availability_zone = "${data.aws_availability_zones.available.names[0]}"
  default_for_az    = true
}

resource "aws_instance" "test" {
  count = "${var.count}"

  ami           = "${data.aws_ami.test.id}"
  instance_type = "t2.medium"
  subnet_id     = "${data.aws_subnet.test.id}"
}

resource "aws_ebs_volume" "test" {
  count = "${var.count}"

  availability_zone = "${element(aws_instance.test.*.availability_zone, count.index)}"
  size              = "10"
  type              = "gp2"
}

resource "aws_volume_attachment" "test" {
  count = "${var.count}"

  device_name = "/dev/xvdg"
  instance_id = "${element(aws_instance.test.*.id, count.index)}"
  volume_id   = "${element(aws_ebs_volume.test.*.id, count.index)}"
}

[bflad]

This appears to be a duplicate of #83 -- closing to consolidate discussions there.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!