Disabling disks is not possible

[ghtyrant]

Version Reports:

Distro version of host:

Debian GNU/Linux 9.5 (stretch)

Terraform Version Report

terraform v0.11.8

• provider.libvirt (unversioned)

I built this provider from source since Debian ships with libvirt 3.0.0, which doesn't work with the pre-built binaries.

Libvirt version

3.0.0

terraform-provider-libvirt plugin version (git-hash)

4cc6d3ba0180c5c1afcbd2f37cbe8f6f8d93ccae

---

Description of Issue/Question

I want to be able to create/add disks conditionally. I have a skeleton main.tf with several configuration (.tfvars) files to create a bunch of VMs. These VMs can be configured to have optional data disks.
As far as I understand, this is not possible currently. I can have count = "${var.data_disk > 0 ? 1 : 0}" to only create the disk when data_disk is specified, but I can't disable the disk block inside the domain.

AFAIK other providers solve this by having pivot resources, e.g.:

resource "libvirt_disk" "mydatadisk" {
    domain_id = "${libvirt_domain.mydomain.id}"
    volume_id = "${libvirt_volume.myvolume}"
    scsi = true
}

That way, I can disable both libvirt_volume and libvirt_disk by setting their count to 0, resulting in no volume being created and no disk being attached to the domain.

Setup

variable "name" {
  type = "string"
  description = "Name of the virtual machine"
}

variable "address" {
  type = "string"
  description = "Address of the virtual machine"
}

variable "cores" {
  type = "string"
  description = "Number of cores"
}

variable "memory" {
  type = "string"
  description = "Amount of RAM in MB"
}

variable "os_disk" {
  type = "string"
  description = "Size of OS disk in bytes"
}

variable "data_disk" {
  type = "string"
  description = "Size of data disk in bytes (optional)"
  default = 0
}

resource "libvirt_volume" "os_disk" {
  name = "${var.name}_os"
  pool = "vg0"
  size = "${var.os_disk}"
}

resource "libvirt_volume" "data_disk" {
  #count = "${var.data_disk > 0 ? 1 : 0}"
  name = "${var.name}_data"
  pool = "data"
  size = "${var.data_disk}"
  format = "qcow2"

  lifecycle {
    prevent_destroy = true
  }
}

resource "libvirt_domain" "domain" {
  name = "${var.name}"

  running   = true
  autostart = true

  disk {
    file = "/home/tyrant/salt-minion-debian-preseed/images/debian-9.5-amd64-CD-1.iso"
  }

  disk {
    volume_id = "${libvirt_volume.os_disk.id}"
  }

  disk {
    volume_id = "${libvirt_volume.data_disk.id}"
  }

  console {
    type        = "pty"
    target_type = "serial"
    target_port = "0"
  }

  console {
    type        = "pty"
    target_type = "virtio"
    target_port = "1"
  }
  vcpu = "${var.cores}"
  memory = "${var.memory}"
}

myvm.tfvars:

name = "myvm"
cores = 4
memory = 512
address = "192.168.100.4"
os_disk = 4294967296

Run terraform apply -var-file=myvm.tfvars

[MalloZup]

@ghtyrant hi! thank you for the issue.

I never tried that feature out (having something conditional). How could your feature being impacted with the new Terraform v12 coming soon out? Would we use the same workflow, and could the HCL language solve without that we touch the provider ? ( https://www.hashicorp.com/blog/terraform-0-1-2-preview)
THX!

[ghtyrant]

Thanks for that link, I wasn't even aware of Terraform v12!

The changes to HCL would definitely solve this issue, especially For and For-Each and maybe even Conditional operator improvements.
Loops allow me to specify the data disks as a list of their size - an empty list results in no volumes and no disk blocks inside domain.
I'm not sure if I could use Conditionals to somehow assign null to the disk-block. If it's possible, that would be another way to solve this.

[zeenix]

We recently upgraded to TF v12 so I guess that solves your problem? So I'd close this one.

[MalloZup]

@zeenix thx! yop closing this