Dynamic resources for_each output in terraform module

Question

Terraform v1.0.0 Provider: aws v3.49.0

I created dynamic AWS subnets resources with a for_each from a module.

The resources creation is working fine, however being able to output dynamically created resources is not working and cannot find proper documentation for it.

The subnet module is

 resource "aws_subnet" "generic" { vpc_id = var.vpc_id cidr_block = var.cidr_block map_public_ip_on_launch = var.public_ip_on_launch tags = { Name = var.subnet_tag_name Environment = var.subnet_environment } }

With simple module output defined

 output "subnet_id" { value = aws_subnet.generic.id }

Then from root module, I am creating a for_each loop over a list variable to create multiple dynamic resources from the module

 module "subnets" { source = "../modules/networking/subnet" for_each = var.subnets vpc_id = "vpc-09d6d4c17544f3a49" cidr_block = each.value["cidr_block"] public_ip_on_launch = var.public_ip_on_launch subnet_environment = var.subnet_environment subnet_tag_name = each.value["subnet_tag_name"] }

When I run this without defining outputs in the root module, things get created normally. The problem comes when I try to define the outputs

 output "subnets" { value = module.subnets.*.id description = "Imported VPC ID" }

It comes up with this error

 │ Error: Unsupported attribute │ │ on output.tf line 2, in output "subnets": │ 2: value = module.subnets.*.id │ │ This object does not have an attribute named "id".

I tried different output definitions. Would appreciate guidance on how to properly define outputs of instances dynamically created with a for_each module.

Answer 1

Per the Terraform documentation , the "splat" operator ( * ) can only be used with lists, and since you're using for_each your output will be a map.

You need to use map/list comprehension to achieve what you want.

For an output that is a map of key/value pairs (note that I've changed the output description to something that makes more sense):

output "subnets" {
    value = {
        for k, v in module.subnets:
        k => v.subnet_id
    }
    description = "Subnet IDs"
}

For a list that only contains the subnet IDs:

output "subnets" {
    value = [
        for k, v in module.subnets:
        v.subnet_id
    ]
    description = "Subnet IDs"
}