Terraform : module output

Question

We have three workspaces into app.terraform.io,

TEST
DEV
PRO

Those workspaces have variables.

I get the value of with that variables with...

variable "environment" {}

I want use this variable to select what resources or modules load.

resource "aws_directory_service_directory" "ds" {
  count = "${var.environment == "TEST" ? 0 : 1}"
  
  name       = "example.com"
  short_name = "example"
  password   = "******"
  type       = "MicrosoftAD"
}

This works but...

The usual output for this resource is ...

output id {
  description = "The ID of the directory"
  value       = aws_directory_service_directory.ds.id
}

output access_url {
  description = "The access URL for the directory"
  value       = aws_directory_service_directory.ds.access_url
}

output dns_ip_addresses {
  description = "A list of IP addresses of the DNS servers for the directory or connector"
  value       = aws_directory_service_directory.ds.dns_ip_addresses
}

output security_group_id {
  description = "The ID of the security group created by the directory"
  value       = aws_directory_service_directory.ds.security_group_id
}

But if I use the count atribute, hte output fails with ...

Because aws_directory_service_directory.ds has "count" set, its attributes
must be accessed on specific instances.

For example, to correlate with indices of a referring resource, use:
    aws_directory_service_directory.ds[count.index]

mixture of literal strings and interpolations. This deprecation applies only
to templates that consist entirely of a single interpolation sequence.


Error: Missing resource instance key

  on outputs.tf line 51, in output "security_group_id":
  51:   value       = aws_directory_service_directory.ds.security_group_id

Because aws_directory_service_directory.ds has "count" set, its attributes
must be accessed on specific instances.

For example, to correlate with indices of a referring resource, use:
    aws_directory_service_directory.ds[count.index]

What would be the rigth output?

I tried:

output id {
  description = "The ID of the directory"
  value       = aws_directory_service_directory.ds[0].id
}

and:

output id {
  description = "The ID of the directory"
  value       = aws_directory_service_directory.ds[1].id
}

But doesn't work (neither)

  on outputs.tf line 36, in output "id":
  36:   value       = aws_directory_service_directory.ds[0].id
    |----------------
    | aws_directory_service_directory.ds is empty tuple

The given key does not identify an element in this collection value.

Error: Invalid index

  on outputs.tf line 36, in output "id":
  36:   value       = aws_directory_service_directory.ds[1].id
    |----------------
    | aws_directory_service_directory.ds is tuple with 1 element

The given key does not identify an element in this collection value.

I tried to see how it's done into, for example https://github.com/terraform-aws-modules/terraform-aws-vpc

output "vpc_id" {
  description = "The ID of the VPC"
  value       = concat(aws_vpc.this.*.id, [""])[0]
}

so ...

output id {
  description = "The ID of the directory"
  value       = concat(aws_directory_service_directory.*.id, [""])[0]
}

but ...

Error: Invalid reference

  on outputs.tf line 36, in output "id":
  36:   value       = concat(aws_directory_service_directory.*.id, [""])[0]

A reference to a resource type must be followed by at least one attribute
access, specifying the resource name.

BinaryMonster BinaryMonster · Accepted Answer · 2020-10-30T09:49:41

Well nothing complex, it's just that output is looking for the resource which is not created, as terraform is still referring to that resource due to which it is throwing an error.

While there are several ways to tackle this issue, one of them is to concatenate all the resources as list in one step, and retrieve a single element using terraform in-built functions.

Your output should be something like this when you are using count as a condition to create resources. If the resource is created the output will be the id of the resource. When the count is zero, output will be empty without any errors.

output id {
  description = "The ID of the directory"
  value       = element(concat(aws_directory_service_directory.ds.*.id, list("")), 0)
}

Terraform : module output

1 Answers