Unexpected diff in rendered template file about terraform-provider-template HOT 2 OPEN

Indeed, I've seen this same behaviour more than a year later, using version 1.0.0 of this provider

from terraform-provider-template.

Hi all,

The cause of this is actually in Terraform Core itself rather than in the provider. The issue is that depends_on for data resources currently forces Terraform to always defer the data source read to apply time, since depends_on doesn't give enough information for Terraform to know whether the resource is depending on an apply-time side-effect of the dependency. This limitation is captured in hashicorp/terraform#17034.

The workaround for now is to use implicit rather than explicit dependencies, which tells Terraform a specific attribute of the other object that is needed before the data resource can be processed and thus allows Terraform to recognize that it is safe to read it during the plan step. In this case this can be achieved by reading the bucket name through the other data resource, thus creating that dependency:

data "aws_s3_bucket_object" "archive" {
  bucket = "${var.bucket}"
  key    = "${var.product}/${var.service}/${var.service}-${var.version}.zip"
}

data "template_file" "user_data" {
  template   = "${file("${path.module}/templates/userdata.ps1")}"

  vars = {
    bucket  = "${data.aws_s3_bucket_object.archive.bucket}"
    key     = "${var.product}/${var.service}/${var.service}-${var.version}.zip"
    service = "${var.service}"
    version = "${var.version}"
  }
}

To eventually resolve hashicorp/terraform#17034 in Terraform Core we intend to adjust the lifecycle of data sources slightly so that the steps can happen in the right order to allow depends_on to work in a more useful way. That work has been on hold while we've been working on the 0.12 release but we will dig into some further design/prototyping for it afterwards.

from terraform-provider-template.