Setting iops for gp2 block device in launch configuration causes recreation of instances

[ghost]

This issue was originally opened by @rsheldon as hashicorp/terraform#17745. It was migrated here as a result of the provider split. The original body of the issue is below.

---

Terraform Version

Terraform v0.11.3

Terraform Configuration Files

variable "root_volume_size" {
  description = "Size (in GB) that you want the root volume to be"
  default = 20
}

variable "data_volume_iops" {
  description = "IOPS that you want the data volume to be (used for RabbitMQ data). Only effective when data_volume_type=io1 "
  default = 1500
}

variable "data_volume_size" {
  description = "Size (in GB) that you want the data volume to be (used for RabbitMQ data)"
  default = 50
}

variable "data_volume_type" {
  description = "EBS volume type that you want the data volume to be (used for RabbitMQ data). eg. gp2 (default) or io1 (higher throughput)"
  default = "gp2"
}

resource "aws_launch_configuration" "rabbit_launch_config" {
  name_prefix = "${var.name}-lc-"
  image_id = "${var.ami}"
  instance_type = "${var.instance_type}"
  iam_instance_profile = "${data.aws_iam_instance_profile.rmq_instance_profile.name}"
  key_name = "${var.aws_keypair_name}"
  security_groups = ["${var.security_group_ids}"]
  user_data = "${data.template_file.rabbitmq_cloud_init.rendered}"

  root_block_device {
    volume_type = "gp2"
    volume_size = "${var.root_volume_size}"
  }

  ebs_block_device {
    device_name = "/dev/sdf"
    volume_type = "${var.data_volume_type}"
    volume_size = "${var.data_volume_size}"
    iops        = "${var.data_volume_iops}"
  }

  lifecycle {
    create_before_destroy = true
  }
}

Expected Behavior

When I run terraform apply after making no new changes, it says that I don't have any changes.

Actual Behavior

If I run plan immediately after I have run apply it should detect no differences. However, it says it needs to recreate the block device again. I have tracked this down to me setting (well defaulting) IOPS on the block device, when using a "gp2" device type.

I can work around this by changing my code to be

  ebs_block_device {
    device_name = "/dev/sdf"
    volume_type = "${var.data_volume_type}"
    volume_size = "${var.data_volume_size}"
    iops        = "${var.data_volume_type == "io1" ? var.data_volume_iops : 0}"
  }

I was defaulting the IOPS to 1500. If IOPS is not applicable for the "gp2" data type, then it should be ignored (whether it's set or not).

Steps to Reproduce

terraform init
terraform apply
terraform plan

Additional Context

References

I think these may be related:
#3239
#72

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