Kubernetes override public DNS name

How can I rewrite some publicly resolvable foo.example.com to an in-cluster service?

kubectl run curl \
--stdin --tty --rm \
--image=radial/busyboxplus:curl

nslookup foo.example.com

As expected, it’s unable to resolve|curl:

Server:    10.152.183.10
Address 1: 10.152.183.10 kube-dns.kube-system.svc.cluster.local

nslookup: can't resolve 'foo.example.com'

curl http://foo.example.com:8080/healthy

curl: (6) Couldn't resolve host 'foo.example.com'

Exit the curl pod so that the DNS may be refreshed.

If the cluster uses [CoreDNS]:

kubectl get deployment \
--selector=k8s-app=kube-dns \
--namespace=kube-system \
--output=name

deployment.apps/coredns

Let’s create an in-cluster service to act as the target:

NAMESPACE="example"

kubectl create deployment kuard \
--image=gcr.io/kuar-demo/kuard-amd64:blue \
--port=8080 \
--namespace=${NAMESPACE}

kubectl expose deployment/kuard \
--name=foo \
--port=8080 \
--target-port=8080 \
--namespace=${NAMESPACE}

Recreate the curl Pod and then it should now resolve the cluster Service DNS name:

nslookup foo.example.com

nslookup foo.example.svc.cluster.local
Server:    10.152.183.10
Address 1: 10.152.183.10 kube-dns.kube-system.svc.cluster.local

Name:      foo.example.svc.cluster.local
Address 1: 10.152.183.137 foo.example.svc.cluster.local

And we can curl the service’s endpoint:

curl http://foo.example.com:8080/healthy

ok

Let’s add a rewrite rule to CoreDNS (foo.example.com → foo.example.svc.cluster.local):

KUBE_EDITOR=nano \
kubectl edit configmap/coredns \
--namespace=kube-system

NOTE It would be better to patch the coredns ConfigMap but the CoreDNS config format isn’t JSON|YAML making this more difficult:

kubectl get configmap/coredns \
--namespace=kube-system \
--output=jsonpath=".data.Corefile"`

rewrite name exact foo.example.com foo.example.svc.cluster.local

And you’ll need to recreate the Pod for it to be programmed with the updated CoreDNS config:

nslookup foo.example.com

Server:    10.152.183.10
Address 1: 10.152.183.10 kube-dns.kube-system.svc.cluster.local

Name:      foo.example.com
Address 1: 10.152.183.137 foo.79523386.svc.cluster.local

curl http://foo.example.com:8080/healthy

ok

Now, in-cluster requests to foo.example.com are redirected to the in-cluster service.