(Route53): HostedZone name_servers cannot be an automatic export with self.export_value

[Cameronsplaze]

Describe the bug

If you have two stacks, and want to pass name servers from stack A to stack B, CDK will create the automatic import/export to help. There's no way to set self.export_value on the hosted zone's nameservers export, to keep it declared when re-deploying. (This also blocks removing automatic cross stack references)

Regression Issue

• Select this option if this issue appears to be a regression.

Last Known Working CDK Version

No response

Expected Behavior

If you add self.export_value(hosted_zone.hosted_zone_name_servers) on a export that already exists, it becomes apart of the stack and you can deploy again.

Current Behavior

The main error is it sees the nameserver as a list, which it is. It must be a string:

Template format error: Every Value member must be a string.

I found a way to change it to the string it's expecting in the next section, but since I transformed the object, it no longer can reference the same object/export.

Reproduction Steps

With the following App:

#!/usr/bin/env python3
import os
import aws_cdk as cdk
from example_stacks.example_stacks import ExampleStackA, ExampleStackB

app = cdk.App()
stack_a = ExampleStackA(app, "ExampleStackA")

stack_b = ExampleStackB(
    app, "ExampleStackB",
    hosted_zone=stack_a.hosted_zone,
    imported_hosted_zone=stack_a.imported_hosted_zone,
)

app.synth()

And inside ./example_stacks/example_stacks.py:

from aws_cdk import (
    Stack,
    aws_route53 as route53,
)
from constructs import Construct

class ExampleStackA(Stack):

    def __init__(self, scope: Construct, construct_id: str, **kwargs) -> None:
        super().__init__(scope, construct_id, **kwargs)
        # Normally I import this with `from_hosted_zone_attributes`, but for a contained example:
        self.imported_hosted_zone = route53.PublicHostedZone(
            self,
            "ImportedHostedZone",
            zone_name="hopefully.does.not.exist.com",
        )
        # https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_route53.PublicHostedZone.html
        self.hosted_zone = route53.PublicHostedZone(
            self,
            "HostedZone",
            zone_name="hopefully.does.not.exist.com",
        )


class ExampleStackB(Stack):

    def __init__(self, scope: Construct, construct_id: str, hosted_zone, imported_hosted_zone, **kwargs) -> None:
        super().__init__(scope, construct_id, **kwargs)
        self.ns_record = route53.NsRecord(
            self,
            "NsRecord",
            zone=imported_hosted_zone,
            values=hosted_zone.hosted_zone_name_servers,
            record_name=f"testing.{hosted_zone.zone_name}",
        )

The self.imported_hosted_zone is a domain bought from AWS, so that hosted zone doesn't live in any stack.

Deploy both stacks to your account:

cdk deploy ExampleStackA
cdk deploy ExampleStackB

Then comment out ExampleStackB inside app.py, and deploy A again. (cdk deploy ExampleStackA). You'll get

Delete canceled. Cannot delete export ExampleStackA:ExportsOutputRefImportedHostedZone5BCE6932C2366AAA as it is in use by ExampleStackB.

(Commenting out B because in the normal architecture, I have a one-to-many with one A, and many B's. Sometimes I need to only deploy A too, it's shared resources for everything. BUT more basically, if both stacks in different apps, that'd also hit this).

The normal way to fix this issue, is to add self.export_value(resource) to the end of stack A. When I try to do that with the hosted_zone_name_servers (with self.export_value(self.hosted_zone.hosted_zone_name_servers)):

1. Add self.export_value(self.hosted_zone.hosted_zone_name_servers) to the end of stack A
2. Uncomment B and deploy, so the change can deploy out. (cdk deploy ExampleStackB)

You'll get an error Template format error: Every Value member must be a string.. It's a list of one item.

You can change it away from a list with self.export_value(Fn.join("||", self.hosted_zone.hosted_zone_name_servers)), but then it doesn't recognize it as the same export as before. You'll get:

RuntimeError: Error: exportValue: either supply 'name' or make sure to export a resource attribute (like 'bucket.bucketName')

Even if you set the name and somehow match it to the generated one, it'll complain about duplicates and fail.

And if you import the self.hosted_zone itself from A to B with route53.PublicHostedZone.from_hosted_zone_attributes, then zone.hosted_zone_name_servers is None (which is expected, the docs say so).

---

The only solution I've found so far, is to manually export/import it. This avoids CDK creating the automatic one that's blocking the stack_a deployments:

# Inside Stack A:
        self.export_value(
            Fn.join("||", self.hosted_zone.hosted_zone_name_servers),
            name=f"{construct_id}-HostedZoneNameServers",
        )
# Inside Stack B:
        # Must be a list, that's what `values` is expecting.
        hosted_zone_name_servers = [Fn.import_value(f"{stack_a.stack_name}-HostedZoneNameServers")]

Possible Solution

Ideally to make self.export_value(nameserver) work like all the other objects I can call self.export_value on.

Additional Information/Context

No response

CDK CLI Version

2.171.1 (build a95560c)

Framework Version

No response

Node.js Version

v22.11.0

OS

Fedora 41

Language

Python

Language Version

Python 3.13.0

Other information

No response