Support for ExternalName

[tobberharley]

Resolve services of type ExternalName bases on the externalName or externalIPs:

---

kind: Service
apiVersion: v1
metadata:
name: my-service
namespace: my-namespace
spec:
type: ExternalName
externalName: other-service.other-namespace.svc.cluster.local
externalIPs:
- 192.168.10.10

[networkop]

hey @torbenhinge I've got some time now to look at this. Can you elaborate your usecase?
My understanding is that externalName is used for external lookups from inside the cluster, as described here, so I don't see how this can be useful for outside->in lookups

[svvac]

I suppose exposed ExternalName could just be CNAMEs to the spec.externalName value.

The example OP provided uses an internal DNS but I believe this is not the intended use case of the feature

[morganchristiansson]

Just having a look thru open issues... I'm also confused by this request.

As an example https://github.com/kubernetes-sigs/external-dns supports service with type: ExternalName. But only when using the annotation external-dns.alpha.kubernetes.io/hostname: tenant1.example.org,tenant2.example.org, it adds an alias/CNAME essentially. https://github.com/kubernetes-sigs/external-dns/blob/master/docs/tutorials/externalname.md

Supporting hostname annotation to set CNAME for services with type: LoadBalancer would be useful. If we can support the same annotation as external-dns uses or add our own.