Add AWS ingress_zone_id output with NLB DNS name's Route53 zone id

* DNS zones served by AWS Route53 may use AWS's special alias records
(other DNS providers would use a CNAME) to resolve the ingress NLB.
Alias records require the NLB DNS name's DNS zone id (not the cluster
`dns_zone_id`)

CHANGES.md

@@ -6,6 +6,10 @@ Notable changes between versions.
 
 * Update etcd from v3.3.10 to [v3.3.11](https://github.com/etcd-io/etcd/blob/master/CHANGELOG-3.3.md#v3311-2019-1-11)
 
+#### AWS
+
+* Add `ingress_zone_id` output with the NLB DNS name's Route53 zone for use in alias records ([#380](https://github.com/poseidon/typhoon/pull/380))
+
 #### Addons
 
 * Update kube-state-metrics from v1.4.0 to v1.5.0

aws/container-linux/kubernetes/outputs.tf

@@ -9,6 +9,11 @@ output "ingress_dns_name" {
   description = "DNS name of the network load balancer for distributing traffic to Ingress controllers"
 }
 
+output "ingress_zone_id" {
+  value       = "${aws_lb.nlb.zone_id}"
+  description = "Route53 zone id of the network load balancer DNS name that can be used in Route53 alias records"
+}
+
 # Outputs for worker pools
 
 output "vpc_id" {

aws/fedora-atomic/kubernetes/outputs.tf

@@ -9,6 +9,11 @@ output "ingress_dns_name" {
   description = "DNS name of the network load balancer for distributing traffic to Ingress controllers"
 }
 
+output "ingress_zone_id" {
+  value       = "${aws_lb.nlb.zone_id}"
+  description = "Route53 zone id of the network load balancer DNS name that can be used in Route53 alias records"
+}
+
 # Outputs for worker pools
 
 output "vpc_id" {