[stable/coredns] Failure if serviceType is "LoadBalancer"

[stuartpb]

#12976 added TCP to the default ports used by the CoreDNS service. However, Kubernetes does not allow LoadBalancer services to expose mixed-protocol ports (see kubernetes/kubernetes#23880 et al), so if you specify LoadBalancer as the service type, this is what happens with the chart as is:

Release "example" failed and has been uninstalled: Service "example-coredns" is invalid: spec.ports: Invalid value: []core.ServicePort{core.ServicePort{Name:"udp-53", Protocol:"UDP", Port:53, TargetPort:intstr.IntOrString{Type:0, IntVal:53, StrVal:""}, NodePort:0}, core.ServicePort{Name:"tcp-53", Protocol:"TCP", Port:53, TargetPort:intstr.IntOrString{Type:0, IntVal:53, StrVal:""}, NodePort:0}}: cannot create an external load balancer with mix protocols

There's been an enhancement proposal to fix this on Kubernetes's end since January, but the last comment on the PR was 20 days ago. It doesn't look like the fix for this will be making it to kubelet any time soon.

Suggested solution

Until Kubernetes can agree on a fix, the best solution, as I see it, would be for the chart to split the TCP ports into a separate service when the type is LoadBalancer, with an additional field in values.yaml to specify annotations for the Service(s) and a note that you may have to add an annotation for your LoadBalancer implementation to allow this.

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