Add support for forwarding path to dns module (#171)

* add support for forwarding path to dns module

* update README

modules/dns/README.md

@@ -4,7 +4,9 @@ This module allows simple management of Google Cloud DNS zones and records. It s
 
 For DNSSEC configuration, refer to the [`dns_managed_zone` documentation](https://www.terraform.io/docs/providers/google/r/dns_managed_zone.html#dnssec_config).
 
-## Example
+## Examples
+
+### Private Zone
 
 ```hcl
 module "private-dns" {
@@ -21,6 +23,21 @@ module "private-dns" {
 # tftest:modules=1:resources=2
 ```
 
+### Forwarding Zone
+
+```hcl
+module "private-dns" {
+  source          = "./modules/dns"
+  project_id      = "myproject"
+  type            = "forwarding"
+  name            = "test-example"
+  domain          = "test.example."
+  client_networks = [var.vpc.self_link]
+  forwarders      = { "10.0.1.1" = null, "1.2.3.4" = "private" }
+}
+# tftest:modules=1:resources=1
+```
+
 <!-- BEGIN TFDOC -->
 ## Variables
 
@@ -34,7 +51,7 @@ module "private-dns" {
 | *default_key_specs_zone* | DNSSEC default zone signing specifications: algorithm, key_length, key_type, kind. | <code title="">any</code> |  | <code title="">{}</code> |
 | *description* | Domain description. | <code title="">string</code> |  | <code title="">Terraform managed.</code> |
 | *dnssec_config* | DNSSEC configuration: kind, non_existence, state. | <code title="">any</code> |  | <code title="">{}</code> |
-| *forwarders* | List of target name servers, only valid for 'forwarding' zone types. | <code title="list&#40;string&#41;">list(string)</code> |  | <code title="">[]</code> |
+| *forwarders* | Map of {IPV4_ADDRESS => FORWARDING_PATH} for 'forwarding' zone types. Path can be 'default', 'private', or null for provider default. | <code title="map&#40;string&#41;">map(string)</code> |  | <code title="">{}</code> |
 | *peer_network* | Peering network self link, only valid for 'peering' zone types. | <code title="">string</code> |  | <code title="">null</code> |
 | *recordsets* | List of DNS record objects to manage. | <code title="list&#40;object&#40;&#123;&#10;name    &#61; string&#10;type &#61; string&#10;ttl     &#61; number&#10;records &#61; list&#40;string&#41;&#10;&#125;&#41;&#41;">list(object({...}))</code> |  | <code title="">[]</code> |
 | *service_directory_namespace* | Service directory namespace id (URL), only valid for 'service-directory' zone types. | <code title="">string</code> |  | <code title="">null</code> |

modules/dns/main.tf

@@ -44,14 +44,19 @@ resource "google_dns_managed_zone" "non-public" {
 
   dynamic forwarding_config {
     for_each = (
-      var.type == "forwarding" && var.forwarders != null ? [""] : []
+      var.type == "forwarding" &&
+      var.forwarders != null &&
+      length(var.forwarders) > 0
+      ? [""]
+      : []
     )
     content {
       dynamic "target_name_servers" {
         for_each = var.forwarders
-        iterator = address
+        iterator = forwarder
         content {
-          ipv4_address = address.value
+          ipv4_address    = forwarder.key
+          forwarding_path = forwarder.value
         }
       }
     }

modules/dns/variables.tf

@@ -53,11 +53,10 @@ variable "domain" {
   type        = string
 }
 
-# TODO(ludoo): add support for forwarding path attribute
 variable "forwarders" {
-  description = "List of target name servers, only valid for 'forwarding' zone types."
-  type        = list(string)
-  default     = []
+  description = "Map of {IPV4_ADDRESS => FORWARDING_PATH} for 'forwarding' zone types. Path can be 'default', 'private', or null for provider default."
+  type        = map(string)
+  default     = {}
 }
 
 variable "name" {