Changing Variable to a JSON value in the UI makes next Terraform run fail

[felixpelletier]

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Terraform Version

terraform 0.15.3 (I know it's old, but I don't believe the issue is there)
provider v2.2.2

Affected Resource(s)

• prefect_variable

Terraform Configuration Files

resource "prefect_variable" "some_variable" {
  name = "some_variable_name"
  value = jsonencode([])
}

Expected Behavior

After creating the variable, I expected the variable's value to be a JSON.

After modifying the value from "[]" to ["some_value"] (notice the absence of surrounding double-quotes) in the UI and trying to re-apply the terraform plan: I would expect it to convert the JSON to a String so I can decode it and use it.

Actual Behavior

After creating the variable, the value is a string "[]"

Applying the plan results in an error:
Could not get Variable, unexpected error: failed to decode response: json: cannot unmarshal array into Go struct field Variable.value of type string

Even when adding an ignore_changes lifecycle rule, the problem persists. (Which makes sense. It's still a data source).

Steps to Reproduce

1. terraform apply
2. In the Cloud UI, change the value from "[]" to ["some_value"]
3. terraform apply

Important Factoids

N/A

References

N/A

[parkedwards]

thanks for raising @felixpelletier - let us take a look at this

[mitchnielsen]

Alrighty, looks like I was able to replicate this:

First, I created a variable in the Prefect UI and gave it a value of ["some_value"].

Then I created the Terraform config to read that variable as a datasource:

data "prefect_variable" "some_variable" {
  name = "some_variable_name"
}

output "some_variable" {
  value = data.prefect_variable.some_variable.value
}

When I run terraform apply, I get:

Could not get Variable, unexpected error: failed to decode response: json: cannot unmarshal array into Go struct field Variable.value of type string

This makes sense, because what I've stored in the UI is an array. If I modify that array to be a string, I can get this to work:

["some_value"]
"[\"some_value\"]"

This gets me:

Changes to Outputs:
  ~ some_variable = jsonencode(
      ~ [
          + "some_value",
        ]
    )

You can apply this plan to save these new output values to the Terraform state, without changing
any real infrastructure.

Do you want to perform these actions?
  Terraform will perform the actions described above.
  Only 'yes' will be accepted to approve.

  Enter a value: yes


Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Outputs:

some_variable = "[\"some_value\"]"

[mitchnielsen]

So what's the fix? We'll want to change the underlying Terraform Type of Variable values from string to JSON. This is due to changes made fairly recently to Variables in the API to make them JSON objects instead of just strings (example: PrefectHQ/prefect#13543).

We'll go ahead and do that in the provider and publish that change as soon as we can. In the meantime, you should be able to work with plain strings just fine. Using JSON objects (arrays, maps, etc) will be supported once we push that update.

Thanks again @felixpelletier!

[mitchnielsen]

Hi @felixpelletier, we've released v2.5.0 which includes a change to the variable value type to a dynamic Terraform type, which supports more types than just a string. The specific types supported are listed in the docs, and we're definitely open to supporting more types in the future depending on use cases.

Thanks again for reporting this 👍🏼