Terraform: only evaluate the part of a ternary statement that is used

[dansteen]

Terraform Version

0.8.5

Affected Resource(s)

not a specific reasource, but rather the way ternary operations are processed

Terraform Configuration Files

# we only build the the sns topics if the sns_env is the same as the env
resource "aws_sns_topic" "api" {
  count = "${var.env == var.sns_env ? 1 : 0}"
  name = "${var.name}-${var.env}"
}

resource "consul_keys" "api" {
  token = "${var.consul_token}"
  # host url
  key {
    delete = "true"
    path  = "service/app/${var.name}/${var.env}"
    value = "${var.env == var.sns_env ? "${aws_sns_topic.api.arn}" : "none" }"
  }

Expected Behavior

I would expect it not to attempt to evaluate ${aws_sns_topic.api.arn} in a case where var.env != var.sns_env. That way, if that resource is not created things will still work.

Actual Behavior

Instead it attempts to evaluate both parts of the ternary results, and I get the following error in a case where var.env != var.sns_env:

* consul_keys.api_sns: resource count can't reference resource variable: aws_sns_topic.api.arn

Steps to Reproduce

Please list the steps required to reproduce the issue, for example:

1. terraform apply

Thanks!

[osterman]

I have this problem as well... We use count to enable/disable a resource. Unfortunately, it's not working. This snippet is taken from a null_resource.trigger:

green_arn_1 = "${aws_elasticsearch_domain.search.count > 0 ? aws_elasticsearch_domain.search.arn : ""}"

Error:

* null_resource.search: Resource 'aws_elasticsearch_domain.search' not found for variable 'aws_elasticsearch_domain.search.arn'

[dayglojesus]

Obligatory me too post...

We began using this for an AMI auto-select feature in 0.8.4 and discovered this behaviour after upgrading to 0.9.5.

variable "ami" {
  default = ""
}

data "aws_ami" "current_ami" {
  most_recent = true

  filter {
    name   = "tag:os"
    values = ["centos"]
  }

  owners = ["self"]
}

resource "aws_instance" "test" {

  ami = "${var.ami == "" ? data.aws_ami.current_ami.id : var.ami}"

}

Results in:

1 error(s) occurred:

* aws_instance.test: 1 error(s) occurred:

* aws_instance.test: At column 3, line 1: true and false expression types must match; have type unknown and type string in:

${var.ami == "" ? data.aws_ami.current_ami.id : var.ami}

It's a bit of a showstopper for us.

[apparentlymart]

@dayglojesus in your case I think you are seeing #14399 rather than this issue. That was just a straight regression in the latest release, and a fix is ready for the next release.

[dayglojesus]

@apparentlymart ah, good to know. thanks!

[hroussez]

I'm running into a similar issue. My code looks like:

variable "enabled" {
  default = false
}

resource "aws_lb" "main" {
  ...
}

resource "aws_lb" "extra" {
  count = "${var.enabled}"
  ...
}

output "extra_dns_name" {
  value = "${var.enabled ? aws_lb.extra.dns_name : aws_lb.main.dns_name}"
}

I get the following error:

* output.extra_dns_name: Resource 'aws_lb.extra' not found for variable 'aws_lb.extra.dns_name'

Should I be doing it differently, or should we work on this issue?

EDIT: I found a related issue/workaround here: https://github.com/hashicorp/terraform/issues/2831#issuecomment-298751019

[fractos]

Just hit this too... massively annoying. (0.9.10 and 0.10.3). Modified from the original code but it demonstrates the point:

data "aws_db_instance" "mydb" {
  count                  = "${var.use_db == true ? 1 : 0}"
  db_instance_identifier = "db-whatever"
}

data "template_file" "task_worker" {
  template = "${file("./task-definitions/worker.jsontemplate")}"

  vars {
    database_host            = "${var.use_db == true ? data.aws_db_instance.mydb.address : ""}"
  }
}

gives

Error running plan: 1 error(s) occurred:

* data.template_file.task_worker: 1 error(s) occurred:

* data.template_file.task_worker: Resource 'data.aws_db_instance.mydb' not found for variable 'data.aws_db_instance.mydb.address'

[JoseIbanez]

Just tested in v0.10.8 for a counter:

resource "aws_route" "route-n" {
  count                   = "${length(var.nfvs)}"
  route_table_id          = "${aws_route_table.RT_OUT.*.id[count.index]}"
  destination_cidr_block  = "99.99.0.1/32"
  network_interface_id    = "${count.index + 1  < length(var.nfvs) ? aws_network_interface.eni_OUT.*.id[count.index+1] : aws_network_interface.RO_eni_OUT.id }"
}

i get this error:

Error: Error running plan: 1 error(s) occurred:
* aws_route.route-n: 1 error(s) occurred:
* aws_route.route-n[1]: index 2 out of range for list aws_network_interface.eni_OUT.*.id (max 2) in:
${count.index + 1  < length(var.nfvs) ? aws_network_interface.eni_OUT.*.id[count.index+1] : aws_network_interface.RO_eni_OUT.id }

[m4ce]

Same problem here with index out of range ... had to switch back to element()

[apparentlymart]

Hi @dansteen, and everyone else here! Sorry about this limitation and thanks for reporting it.

This is the same issue being discussed in #11566. As mentioned there, a new version of the interpolation evaluator is coming which fixes this and many other limitations. Since we already have that issue open I'm going to close this one just to consolidate the discussion over there. That issue also contains some example workarounds for certain situations, which may be useful in the short term.

[s2504s]

As workaround I use method join for resource which is presented as an array *

resource "aws_sns_topic" "api" {
  count = "${var.env == var.sns_env ? 1 : 0}"
  name = "${var.name}-${var.env}"
}
If using:
resource "consul_keys" "api" {
  token = "${var.consul_token}"
  # host url
  key {
    delete = "true"
    path  = "service/app/${var.name}/${var.env}"
    value = "${var.env == var.sns_env ? "${join("", aws_sns_topic.api.*.arn)}" : "none" }"
  }

[hashibot[bot]]

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