Terraform - data depends-on data

user_1842160 0
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I am using data external and data local_file in my terraform code. data external executes a script and create a json file. Now my data local_file has to read the json file.

data "external" "example" {
   program = ["python", "XXXXX.py", "${var.fileName}"]
}

data "local_file" "dashboard" {
    filename = "${path.module}/dashboardData.json"
}

Here data local_file is dependent on data external for the json file.

Is there a work aroud ?

terraform json
2 Answers

If your external data source outputs the filename you could use Terraform's interpolation to force a dependency between the 2 data sources.

So assuming the output of python XXXXX.py fileName gives {"filename": "dashboardData.json"} or similar then you could just use something like this:

data "external" "example" {
  program = ["python", "XXXXX.py", "${var.fileName}"]
}

data "local_file" "dashboard" {
  filename = "${path.module}/${data.external.example.result.filename}"
}

Because the local_file data source now refers to the external data source it will force Terraform to wait for the external data source to complete.

An alternative is to set an explicit dependency between them by using depends_on:

data "external" "example" {
  program = ["python", "XXXXX.py", "${var.fileName}"]
}

data "local_file" "dashboard" {
  filename   = "${path.module}/dashboardData.json"
  depends_on = [data.external.example]
}
user_22913210

If you want to force terraform to defer evaluating one value until after another is known, and there isn't an existing data source that covers your use case, you can use null_data_source as a stand-in.

data "null_data_source" "dashboard_file" {
  depends_on = [ "data.external.example.result" ]
  inputs = {
    name = "${path.module}/dashboardData.json"
  }
}

When the dependencies are met, terraform will evaluate all the inputs of the null_data_source, do nothing, and then expose all the results as outputs.

Now, you can refer to data.null_data_source.dashboard_file.outputs.name, and terraform knows that it must first compute data.external.example.result before it's allowed to use that value.

user_38212020
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