Terraform: creation of resources with nested loop

Question

I have created a bunch of VPC endpoints in one AWS account and need to share them with other VPCs across different accounts. Break down of my terraform code is provided below.

• Created the Route53 private hosted zones (Resource#1 for easy reference) as below

resource "aws_route53_zone" "private" {
  for_each      = local.vpc_endpoints

  name = each.value.phz

  vpc {
    vpc_id = var.vpc_id
  }

  lifecycle {
    ignore_changes = [vpc]
  }

  tags = {
    Name = each.key
  }
}

• Created vpc association authorizations (Resource#2). The VPC ID, to which the endpoints are to be shared is passed as a variable as shown below.

resource "aws_route53_vpc_association_authorization" "example" {
  for_each      = local.vpc_endpoints

  vpc_id  = var.vpc
  zone_id = aws_route53_zone.private[each.key].zone_id
}

• Finally, I have created the VPC associations (Resource#3)

resource "aws_route53_zone_association" "target" {
  for_each = aws_route53_vpc_association_authorization.example
  provider = aws.target-account

  vpc_id  = aws_route53_vpc_association_authorization.example[each.key].vpc_id
  zone_id = aws_route53_vpc_association_authorization.example[each.key].zone_id
}

Everything works fine for the first VPC (vpc-A). But now I need to share the same hosted zones (Resource#1) with a different VPC (vpc-B) and more VPCs in the future. This means I need to repeat the creation of "aws_route53_vpc_association_authorization" (Resource#2) for all new VPCs as well, ideally looping through a list of VPC IDs. But I am unable to it as nested for_each loop is not supported. Tried other options like count + for_each etc., but nothing help.

Could you provide some guidance on how to achieve this?