External volume get destroyed on instance increas

[heino-vdbh]

I use this module and attach a external volume as shown in the examples.
But when I increase the instance_count the volume get destroyed and recreated.

module "webserver" {
  source                                    = "terraform-aws-modules/ec2-instance/aws"
  version                                    = "~> 2.0"
  name                                       = "${var.ec2_name}"
  instance_count                       = "${var.instance_count}"
  ami                                          = data.aws_ami.centos7.id
  instance_type                         = "${var.instance_type}"
  key_name                                = "${var.key_name}"
  monitoring                              = "${var.monitoring}"
  vpc_security_group_ids.         = ["${module.webserver_sg.this_security_group_id}"]
  subnet_ids                              = data.terraform_remote_state.vpc.outputs.vpc_public_subnets
  associate_public_ip_address = "${var.associate_public_ip_address}"

  tags                                        = "${var.ec2_tags}"
}

resource "aws_volume_attachment" "webserver" {
  count                = var.instance_count
  device_name.    = "/dev/sdh"
  volume_id          = aws_ebs_volume.webserver[count.index].id
  instance_id        = module.webserver.id[count.index]
}

resource "aws_ebs_volume" "webserver" {
  count                      = var.instance_count
  availability_zone     = module.webserver.availability_zone[count.index]
  size                        = var.ebs_size
  encrypted              = true
  kms_key_id            = data.terraform_remote_state.vpc.outputs.kms_key_arn
  tags = {
    Name = var.instance_count > 1 ? format("%s-%d", var.ec2_name, count.index + 1) : var.ec2_name
  }
}

ERROR

  # aws_ebs_volume.webserver[0] must be replaced
-/+ resource "aws_ebs_volume" "webserver" {
      ~ arn               = "arn:aws:ec2:eu-central-1:123456789012:volume/vol-0ffb96d6967f0e8d0" -> (known after apply)
      ~ availability_zone = "eu-central-1a" -> (known after apply) # forces replacement
        encrypted         = true
      ~ id                = "vol-0ffb96d6967f0e8d0" -> (known after apply)
      ~ iops              = 150 -> (known after apply)
        kms_key_id        = "arn:aws:kms:eu-central-1:123456789012:key/ac63ab1f-9bf8-4d92-97a6-15e162aaeb72"
        size              = 50
      + snapshot_id       = (known after apply)
      ~ tags              = {
          ~ "Name" = "approval" -> "approval-1"
        }
      ~ type              = "gp2" -> (known after apply)
    }

[heino-vdbh]

I have fixed the destroy of the volume by putting the AZs into a variable.

resource "aws_ebs_volume" "webserver" {
  count = var.instance_count


  availability_zone ="${element(var.azs, count.index)}"
  size              = var.ebs_size
  encrypted = true
  kms_key_id = data.terraform_remote_state.vpc.outputs.kms_key_arn

  tags = {
    Name = var.instance_count > 1 ? format("%s-%d", var.ec2_name, count.index + 1) : var.ec2_name
  }
}

[heino-vdbh]

But the aws_volume_attachment of the existing instance get still a forces replacement if i increase the instance_count

-/+ resource "aws_volume_attachment" "webserver" {
        device_name = "/dev/sdh"
      ~ id          = "vai-1312302379" -> (known after apply)
      ~ instance_id = "i-34542354525" -> (known after apply) # forces replacement
        volume_id   = "vol-234532525"
    }

[antonbabenko]

@hniemann I think you can try to use for_each instead of count for this situation and loop through ids instead of count indexes.

Check this for more details - https://www.terraform.io/docs/configuration/resources.html#when-to-use-for_each-instead-of-count

This is not a bug of the module, so I am closing this issue.

[github-actions]

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