Non-destructive update for machine-type change in google_compute_instance

[gionn]

Hi, it would be great if changing the machine-type will trigger a workflow where the instance is stopped, resized and started instead of recreating the VM.

This behaviour is what GCP do via console when a resize is requested.

[danawillow]

It looks like the console requests that you manually stop the instance before resizing, I don't see it happening automatically. Regardless, https://cloud.google.com/compute/docs/reference/latest/instances/setMachineType should easy enough for us to add support for, but I'm wary about stopping the instance to do so (at least in the beginning) since that could be unexpected behavior for the user.

[rosbo]

One idea to handle this:

We could add an extra boolean field called something like allow_stopping_for_update. Defaults would be false. If the machine_type field is updated, the instance is running and allow_stopping_for_update is false, it would fail with an error message saying that allow_stopping_for_update should be enabled or something like that.

There is other properties I believe that we can update only if the instance is stopped. We could support update in the same fashion.

[gionn]

@danawillow you are right and I lied, I've applied a resource resize tip on the console instead (via the yellow lightbulb that appear saying that you can save money changing machine-type), I supposed the standard resize behaviour was the same.

@rosbo it would be great.

FYI, manual resize didn't break anything in terraform, since at the next state refresh it will find the updated machine-types, so as workaround is fine.

Thanks!

[fisabelle]

Does that duplicate #380 ?

[paddycarver]

I think we could take a similar approach to hashicorp/terraform#11998 to make this work.

[ubschmidt2]

The same applies to changes to the assigned service account and the API scopes (e.g. https://github.com/terraform-providers/terraform-provider-google/blob/2a6974451838133bd89ac8e40d09285f91d6da61/google/resource_compute_instance.go#L483).

[ubschmidt2]

@danawillow

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