Support CNAMEs lookups when fetching the ingress's IP address

[abaguas]

A panic occurs when there is an Ingress resource with a load balancer's address configured as a hostname. And this hostname is a CNAME to another record.

How to reproduce

An Ingress resource with the load balancer's address configured as a hostname:

$ kubectl get ingress --namespace my-namespace my-application -o yaml
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  labels:
    app.kubernetes.io/instance: my-application
  name: my-application
  namespace: my-namespace
spec:
   ...
status:
  loadBalancer:
    ingress:
    - hostname: ingress.my-cluster.ks.example.com

And where this hostname is a CNAME:

dig my-application.example.com

; <<>> DiG 9.18.28-0ubuntu0.20.04.1-Ubuntu <<>> my-application.example.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6877
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1220
; COOKIE: 03d578f46f75da8701000000673f91d300536bca8950a7b0 (good)
;; QUESTION SECTION:
;my-application.example.com. IN        A

;; ANSWER SECTION:
my-application.example.com. 60 IN CNAME ingress.my-cluster.ks.example.com.
ingress.my-cluster.ks.example.com. 60 IN CNAME ingress-nginx-controller.kube-system.svc.my-cluster.ks.
ingress-nginx-controller.kube-system.svc.my-cluster.ks. 19 IN A 10.248.224.50
ingress-nginx-controller.kube-system.svc.my-cluster.ks. 19 IN A 10.248.227.104
ingress-nginx-controller.kube-system.svc.my-cluster.ks. 19 IN A 10.248.227.49

Fix

Support CNAME records in addition to A records:

k8gb/controllers/utils/dns.go

Line 68 in 40f7264

ips = append(ips, a.(*dns.A).A.String())

Additional bug

It would be great if the panic log message showed the line where it panics instead of the line of code where the logger emitted the message.

2024-11-21T20:07:53Z ERR github.com/k8gb-io/k8gb/controllers/logging/logr.go:72 > events: Reconciler error {"Gslb":"my-namespace/my-application","controller":"gslb","controllerGroup":"k8gb.absa.oss","controllerKind":"Gslb","name":"my-application","namespace":"my-namespace","reconcileID":"cd328357-973e-43bd-8665-0c4e30e54e86"} error="panic: interface conversion: dns.RR is *dns.CNAME, not *dns.A [recovered]"

Reported in: https://cloud-native.slack.com/archives/C021P656HGB/p1732219873734419