Fix terraform error for nlb type with dualstack

[ramonskie]

Summary

• Fix terraform resource reference error when using --lb-type nlb with --dualstack=true
• Split DNS templates so each LB type references the correct resource type: cf_dns.tf for Classic ELBs (type "cf"), cf_nlb_dns.tf for Network LBs (type "nlb")

Problem

PR #644 introduced a bug where cf_dns.tf conditionally referenced aws_lb.* resources based on var.dualstack, but these resources only exist when state.LB.Type="nlb". This caused terraform to fail with "Reference to undeclared resource" errors when users set --lb-type cf --dualstack=true.

Solution

Split the DNS configuration into separate templates:

• cf_dns.tf - References aws_elb.* resources for type "cf"
• cf_nlb_dns.tf - References aws_lb.* resources for type "nlb"

The template generator now selects the correct DNS template based on state.LB.Type, eliminating the conditional logic mismatch.

[ramonskie]

the pr that introduced the dual stack feature has been reverted in #663
so we can close this

[Copilot]

Pull Request Overview

This PR adds support for Network Load Balancer (NLB) DNS configuration by creating a new template file and updating the template generator to use it when NLB type is specified. The change separates DNS configuration for NLB resources (aws_lb) from classic ELB resources (aws_elb).

• Created cf_nlb_dns.tf template that references aws_lb resources instead of aws_elb resources
• Updated cf_dns.tf to remove conditional logic for dualstack, now only references aws_elb resources
• Added NLB type to the list of supported load balancer types for LB commands

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
terraform/aws/templates/cf_nlb_dns.tf	New DNS template file for NLB that references aws_lb resources
terraform/aws/templates/cf_dns.tf	Simplified to remove dualstack conditionals, now only uses aws_elb resources
terraform/aws/template_generator_test.go	Added test coverage for NLB with and without system domain
terraform/aws/template_generator.go	Updated to load and use the new cf_nlb_dns template for NLB type
commands/aws_lbs.go	Extended LB type switch to include "nlb" alongside "cf"

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[Copilot]

The isolation segment DNS record references aws_elb.iso_router_lb but should reference the NLB resource instead. Based on the pattern in iso_segments.tf, this should be one(aws_lb.iso_router_nlb[*].dns_name) to match the NLB infrastructure that this template is designed for.

Suggested change

	records = [one(aws_elb.iso_router_lb[*].dns_name)]
	records = [one(aws_lb.iso_router_nlb[*].dns_name)]

[peanball]

Please close this. I will prepare another one to ensure that the desired semantics are correct.

I also want to introduce a proper CLI flag for dual stack, not just a TF variable.