for_each is failing not yet created resources

[Menur]

Terraform Version

Terraform v0.12.7

Terraform Configuration Files

terraform {
  required_version = ">= 0.12"
}


provider "aws" {
  region = "us-east-1"
  version = "~> 2.25"
}


locals {
  topics = [
      "topicA",
      "topicB",
  ]
  prefix = "prefix"
}


resource "aws_sns_topic" "topics" {
  for_each = toset(local.topics)
  name     = "${local.prefix}-${each.value}"
}

resource "aws_sqs_queue" "queue" {
  name = "${local.prefix}-Queue"
}


resource "aws_sns_topic_subscription" "subscription" {
  for_each  = toset(values(aws_sns_topic.topics)[*].arn)
  protocol  = "sqs"
  endpoint  = aws_sqs_queue.queue.arn
  topic_arn = each.value
}

Crash Output

https://gist.github.com/Menur/228b400095d0f972226608123a12fde7

Expected Behavior

SQS and two SNS topics should be created and subscribed to SNS

Actual Behavior

!!!!!!!!!!!!!!!!!!!!!!!!!!! TERRAFORM CRASH !!!!!!!!!!!!!!!!!!!!!!!!!!!!

Terraform crashed! This is always indicative of a bug within Terraform.
A crash log has been placed at "crash.log" relative to your current
working directory. It would be immensely helpful if you could please
report the crash with Terraform[1] so that we can fix this.

When reporting bugs, please include your terraform version. That
information is available on the first line of crash.log. You can also
get it by running 'terraform --version' on the command line.

[1]: https://github.com/hashicorp/terraform/issues

!!!!!!!!!!!!!!!!!!!!!!!!!!! TERRAFORM CRASH !!!!!!!!!!!!!!!!!!!!!!!!!!!!

Steps to Reproduce

1. terraform init
2. terraform plan

Additional Context

When SNS topics aren't created terraform will crash.
When SNS topics are created terraform will proceed.

[pselle]

@Menur Currently working on a fix for this panic, but the case you're writing will error/won't work, because the values passed to for_each must be known. Once this is fixed, you'll get the following error, but the described work-around will help you in the present:

Error: Invalid for_each argument

The "for_each" value depends on resource attributes that cannot be determined
until apply, so Terraform cannot predict how many instances will be created.
To work around this, use the -target argument to first apply only the
resources that the for_each depends on.

Thank you for the report!

[Menur]

Know means constant, right?
Passing values to foreach from data or variable results in crash too.

data "aws_caller_identity" "current" {}
data "aws_region" "current" {}

locals {
  topicARNs = [
    for messageName in local.topics : "arn:aws:sns:${data.aws_region.current.name}:${data.aws_caller_identity.current.account_id}:${local.prefix}-${messageName}"    
  ]
}

resource "aws_sns_topic_subscription" "subscription" {
  for_each  = toset(local.topicARNs) ##toset(values(aws_sns_topic.topics)[*].arn)
  protocol  = "sqs"
  endpoint  = aws_sqs_queue.queue.arn
  topic_arn = each.value
  depends_on = [aws_sns_topic.topics]
}

When region name and account_id are specified as constant strings in locals it works.

[pselle]

@Menur Known doesn't mean constant, it's a bit different.

Sorry to confirm that the crash will still happen with known values on the current release of Terraform -- my instructions for the work around (-target) was hoping to help you in the meantime. Meanwhile, the fix is merged upstream, so things will improve once 0.12.8 is released.

[Menur]

-target is helpful and it works.

[pselle]

@Menur Thanks so much for the report back! I'll close this issue when the upstream fix is released :)

[pselle]

0.12.8 is out! https://www.terraform.io/downloads.html

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.