Adding nameservers to kubernetes

Question

I'm using Kubernetes v1.0.6 on AWS that has been deployed using kube-up.sh.
Cluster is using kube-dns.

$ kubectl get svc kube-dns --namespace=kube-system
NAME       LABELS                                                                           SELECTOR           IP(S)       PORT(S)
kube-dns   k8s-app=kube-dns,kubernetes.io/cluster-service=true,kubernetes.io/name=KubeDNS   k8s-app=kube-dns   10.0.0.10   53/UDP

Which works fine.

$ kubectl exec busybox -- nslookup kubernetes.default
Server:    10.0.0.10
Address 1: 10.0.0.10 ip-10-0-0-10.eu-west-1.compute.internal

Name:      kubernetes.default
Address 1: 10.0.0.1 ip-10-0-0-1.eu-west-1.compute.internal

This is the resolv.conf of a pod.

$ kubectl exec busybox -- cat /etc/resolv.conf
nameserver 10.0.0.10
nameserver 172.20.0.2
search default.svc.cluster.local svc.cluster.local cluster.local eu-west-1.compute.internal

Is it possible to have the containers use an additional nameserver?

I have a secondary DNS based service discovery Oon let's say 192.168.0.1) that I would like my kubernetes containers to be able to use for dns resolution.

ps. A kubernetes 1.1 solution would also be acceptable :)

Thank you very much in advance, George

Answer 1

The DNS addon README has some details on this. Basically, the pod will inherit the resolv.conf setting of the node it is running on, so you could add your extra DNS server to the nodes' /etc/resolv.conf. The kubelet also takes a --resolv-conf argument that may provide a more explicit way for you to inject the extra DNS server. I don't see that flag documented anywhere yet, however.

Answer 2

In Kuberenetes (probably) 1.2 we'll be moving to a model where nameservers are assumed to be fungible. There are too many resolvers that break when different nameservers serve different subsets of DNS, and there is no real specification here that we can point to.

In other words, we'll start dropping the host's nameserver records from the container's merged resolv.conf and making our own DNS server the only nameserver line. Our DNS will be able to forward requests to upstream nameservers.