Can't avoid hardcoding interface:scsi

[jsoref]

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Terraform Version

Terraform v0.12.16
+ provider.google v3.3.0

Affected Resource(s)

• google_compute_instance_template

Terraform Configuration Files

provider google {
  version = "~> 3.0"
}

resource "google_compute_instance_template" "node" {
  name         = "node"
  machine_type = "n1-standard-1"
  can_ip_forward = false

  disk {
    source_image = "https://www.googleapis.com/compute/v1/projects/debian-cloud/global/images/family/debian-9"
    disk_size_gb = 10
    disk_type    = "pd-ssd"
    boot         = true
    mode         = "READ_WRITE"
    type         = "PERSISTENT"
  }

  network_interface {
    network = "default"
  }
}

resource "google_compute_instance_template" "node-scsi" {
  name         = "node-scsi"
  machine_type = "n1-standard-1"
  can_ip_forward = false

  disk {
    source_image = "https://www.googleapis.com/compute/v1/projects/debian-cloud/global/images/family/debian-9"
    disk_size_gb = 10
    disk_type    = "pd-ssd"
    boot         = true
    mode         = "READ_WRITE"
    type         = "PERSISTENT"
    interface    = "SCSI"
  }

  network_interface {
    network = "default"
  }
}

Debug Output

Panic Output

Expected Behavior

A similarly manually created template doesn't declare a scsi interface -- which to me means that in theory it could change if google updates their defaults (which is perhaps something i might want):

creationTimestamp: '...'
description: ''
id: '...'
kind: compute#instanceTemplate
name: node-native
properties:
  canIpForward: false
  disks:
  - autoDelete: true
    boot: true
    deviceName: boot
    index: 0
    initializeParams:
      diskSizeGb: '10'
      diskType: pd-ssd
      sourceImage: https://www.googleapis.com/compute/v1/projects/debian-cloud/global/images/family/debian-9
    kind: compute#attachedDisk
    mode: READ_WRITE
    type: PERSISTENT
  machineType: n1-standard-1
  metadata:
    fingerprint: ...
    kind: compute#metadata
  networkInterfaces:
  - kind: compute#networkInterface
    network: https://www.googleapis.com/compute/v1/projects/.../global/networks/default
  scheduling:
    automaticRestart: true
    onHostMaintenance: MIGRATE
    preemptible: false
  serviceAccounts:
  - email: [email protected]
    scopes:
    - https://www.googleapis.com/auth/devstorage.read_only
    - https://www.googleapis.com/auth/logging.write
    - https://www.googleapis.com/auth/monitoring.write
    - https://www.googleapis.com/auth/service.management.readonly
    - https://www.googleapis.com/auth/servicecontrol
    - https://www.googleapis.com/auth/trace.append
selfLink: https://www.googleapis.com/compute/v1/projects/.../global/instanceTemplates/node-native

Actual Behavior

plan output:

Terraform will perform the following actions:

  # google_compute_instance_template.node will be created
  + resource "google_compute_instance_template" "node" {
      + can_ip_forward       = false
      + id                   = (known after apply)
      + machine_type         = "n1-standard-1"
      + metadata_fingerprint = (known after apply)
      + name                 = "node"
      + name_prefix          = (known after apply)
      + project              = (known after apply)
      + region               = (known after apply)
      + self_link            = (known after apply)
      + tags_fingerprint     = (known after apply)

      + disk {
          + auto_delete  = true
          + boot         = true
          + device_name  = (known after apply)
          + disk_size_gb = 10
          + disk_type    = "pd-ssd"
          + interface    = (known after apply)
          + mode         = "READ_WRITE"
          + source_image = "https://www.googleapis.com/compute/v1/projects/debian-cloud/global/images/family/debian-9"
          + type         = "PERSISTENT"
        }

      + network_interface {
          + network            = "default"
          + subnetwork         = (known after apply)
          + subnetwork_project = (known after apply)
        }

      + scheduling {
          + automatic_restart   = (known after apply)
          + on_host_maintenance = (known after apply)
          + preemptible         = (known after apply)

          + node_affinities {
              + key      = (known after apply)
              + operator = (known after apply)
              + values   = (known after apply)
            }
        }
    }

  # google_compute_instance_template.node-scsi will be created
  + resource "google_compute_instance_template" "node-scsi" {
      + can_ip_forward       = false
      + id                   = (known after apply)
      + machine_type         = "n1-standard-1"
      + metadata_fingerprint = (known after apply)
      + name                 = "node-scsi"
      + name_prefix          = (known after apply)
      + project              = (known after apply)
      + region               = (known after apply)
      + self_link            = (known after apply)
      + tags_fingerprint     = (known after apply)

      + disk {
          + auto_delete  = true
          + boot         = true
          + device_name  = (known after apply)
          + disk_size_gb = 10
          + disk_type    = "pd-ssd"
          + interface    = "SCSI"
          + mode         = "READ_WRITE"
          + source_image = "https://www.googleapis.com/compute/v1/projects/debian-cloud/global/images/family/debian-9"
          + type         = "PERSISTENT"
        }

      + network_interface {
          + network            = "default"
          + subnetwork         = (known after apply)
          + subnetwork_project = (known after apply)
        }

      + scheduling {
          + automatic_restart   = (known after apply)
          + on_host_maintenance = (known after apply)
          + preemptible         = (known after apply)

          + node_affinities {
              + key      = (known after apply)
              + operator = (known after apply)
              + values   = (known after apply)
            }
        }
    }

describe output:

$ gcloud compute instance-templates describe node
creationTimestamp: '...'
description: ''
id: '...'
kind: compute#instanceTemplate
name: node
properties:
  disks:
  - autoDelete: true
    boot: true
    deviceName: persistent-disk-0
    index: 0
    initializeParams:
      diskSizeGb: '10'
      diskType: pd-ssd
      sourceImage: https://www.googleapis.com/compute/v1/projects/debian-cloud/global/images/family/debian-9
    interface: SCSI
    kind: compute#attachedDisk
    mode: READ_WRITE
    type: PERSISTENT
  machineType: n1-standard-1
  metadata:
    fingerprint: JTqYaJW_BVs=
    kind: compute#metadata
  networkInterfaces:
  - kind: compute#networkInterface
    network: https://www.googleapis.com/compute/v1/projects/.../global/networks/default
  scheduling:
    automaticRestart: true
    onHostMaintenance: MIGRATE
    preemptible: false
selfLink: https://www.googleapis.com/compute/v1/projects/.../global/instanceTemplates/node

$ gcloud compute instance-templates describe node-scsi
creationTimestamp: '...'
description: ''
id: '...'
kind: compute#instanceTemplate
name: node-scsi
properties:
  disks:
  - autoDelete: true
    boot: true
    deviceName: persistent-disk-0
    index: 0
    initializeParams:
      diskSizeGb: '10'
      diskType: pd-ssd
      sourceImage: https://www.googleapis.com/compute/v1/projects/debian-cloud/global/images/family/debian-9
    interface: SCSI
    kind: compute#attachedDisk
    mode: READ_WRITE
    type: PERSISTENT
  machineType: n1-standard-1
  metadata:
    fingerprint: JTqYaJW_BVs=
    kind: compute#metadata
  networkInterfaces:
  - kind: compute#networkInterface
    network: https://www.googleapis.com/compute/v1/projects/.../global/networks/default
  scheduling:
    automaticRestart: true
    onHostMaintenance: MIGRATE
    preemptible: false
selfLink: https://www.googleapis.com/compute/v1/projects/.../global/instanceTemplates/node-scsi

Steps to Reproduce

1. terraform apply
2. gcloud compute instance-templates describe node-native
3. gcloud compute instance-templates describe node
4. gcloud compute instance-templates describe node-scsi

Important Factoids

I have pre-existing manually created templates that I kind of like. I'd like to migrate to using terraform w/o losing their characteristics.

(Yes, I understand SCSI is the default today, and the terraform behavior is documented, but it clearly isn't required from gcloud's perspective.)

References

This is in the family of #5283 -- things which do not quite work the way I'd like in that I can't produce the output I'd like the way I'd like / there doesn't appear to be any way to do so using terraform.

b/308756461

[venkykuberan]

@jsoref Is your question is why Terraform is setting SCSI for disk interface?. if so per [https://cloud.google.com/compute/docs/reference/rest/v1/instanceTemplates] (api spec) the default value for disk.interface is SCSI.

Can you please provide a little more detail on what the bug is ?

[venkykuberan]

@jsoref if you aren't looking for help on this issue, shall i go head and close this one ?

[jsoref]

@venkykuberan: sorry. I thought it was plainly obvious. There's no reason that terraform should take the node case which doesn't hard-code scsi and hard-code scsi into the template. Google will on the other side do that.

I'm not sure how else to explain it. Just because Google's backend does something by default doesn't mean your frontend should perform that coercion up front. Let the backend do the conversion.