default_version logic in google_ml_engine_model is broken

[AndreasBergmeier6176]

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Terraform Version

Terraform v1.0.1
on linux_amd64

• provider registry.terraform.io/hashicorp/google v3.90.0
• provider registry.terraform.io/hashicorp/google-beta v3.90.0

Affected Resource(s)

• google_ml_engine_model

Terraform Configuration Files

resource "google_ml_engine_model" "foo" {
  provider = google-beta

  name                              = "foo"
  regions                           = ["europe-west1"]
  online_prediction_logging         = true
  online_prediction_console_logging = true

Expected Behavior

There should be no reference to version in model to begin with.
I expect that this design flaw comes directly from the backend.
With the current behavior I would even add a breaking change and remove default_version handling from Terraform entirely.

Actual Behavior

After deploying a model version, the backend adds the following properties to ModelVersion:

default_version {
  ~ name = "projects/pro/models/foo/versions/bar" -> nil # forces replacement
}

And best of all changing default_version enforces replacement.
Now there are various problems with this.
First off, should I reference a version, it basically creates a chicken/egg problem both for creation and destroying.
Second - currently there is not support for model versions in Terraform so you can only hardcode the value.
Third - adding a default_version at model creation time is not supported either.

Steps to Reproduce

1. terraform apply

b/312911725

[edwardmedia]

@AndreasBergmeier6176 default_version is defined as optional. I don't see api returns if it is not provided in the config. Can you share how you config and your debug log?

[edwardmedia]

default_version cannot be specified at model creation time. But currently the implementation does not support Update. Change label to enhancement for the new functionality.

[AndreasBergmeier6176]

don't see api returns if it is not provided in the config

1. Add a model via Terraform (terraform apply)
2. Add a version (gcloud beta)
3. terraform plan

Result: There is default_version set on model.

This and no support for version in Terraform makes this basically unusable in Terraform.

[slevenick]

Hm, so the issue you are describing is that you have modified a field on this resource outside of Terraform and now Terraform is trying to reconcile that diff? You may want to look into a lifecycle directive to ignore changes on that field as you actively manage it outside of Terraform

It's possible that we should not support the default_version field, but it would be a breaking change to do so at this point

[AndreasBergmeier6176]

You may want to look into a lifecycle directive to ignore changes on that field as you actively manage it outside of Terraform

Thanks, that should do the trick for us.