Change automatic_restart to be computed if not specified

[selmanj]

Fixes #107

[rileykarson]

I definitely agree that the deprecated value should be computed & optional, if not removed entirely.

My concern with setting the second value to computed as well means that when we move from

scheduling {
  automatic_restart = true
}

to

scheduling {
}

Terraform won't see any diffs, and the resource won't get recreated. This means that the second scheduling block doesn't guarantee that the server-side resource's property is false; it can be true if there was an already existing resource and we modified the config.

What happens if the deprecated value is computed and the new one isn't? Especially in the case where users were relying on the old default of true in their configs. I expect we'll have enough diffs/recreates that we need to use Computed like this, but being able to stop that corner case before it happens would be nice as well.

[rileykarson]

Also, linking #224 since this should fix it as well as #107.

[rosbo]

If you set this field to Computed, it means a user cannot specify a value for automatic_restart. GCP default value for this field is true. It means a user could never create an instance with terraform with automatic_restart = false. I am confused about why that would be something desirable.

Am I missing something?

[rileykarson]

To my understanding, Computed means that it can't be set and can only be read, but Computed and Optional means that it acts like it is Computed until a value is set in config, at which point it is treated as Optional.

[rosbo]

Thanks for the clarification, I wasn't aware of this "trick"

[selmanj]

@rosbo The docs on Computed say that you can override the value by setting it in your config:

	// If Computed is true, then the result of this value is computed
	// (unless specified by config) on creation.

[selmanj]

A main problem here is that there's no way to infer whether or not automatic_restart was set explicitly or not. Ideally we want to not specify it all when creating a resource, as GCP will automatically choose the correct value whether or not is_preemptible is specified. We can't do that here unfortunately...

[dgolja]

What about just making sure that you can not define automatic_restart twice in the config file ? This would for sure fix the #224

[selmanj]

Good point @dgolja; this PR is not complete and is off-topic from the original issue. I'll close this for now and submit a new one specifically around removing the deprecated parameter (which has been deprecated since 2015) and fixing scheduling.automatic_restart.

[ghost]

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