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how to see upstream server of coredns in kubernetes 1.10+?

7/25/2018

I have the following configmap

kubectl get configmap coredns --namespace kube-system -o yaml
apiVersion: v1
data:
  Corefile: |
    .:53 {
        errors
        health
        kubernetes cluster.local in-addr.arpa ip6.arpa {
           pods insecure
           upstream
           fallthrough in-addr.arpa ip6.arpa
        }
        prometheus :9153
        proxy . /etc/resolv.conf
        cache 30
        reload
    }
kind: ConfigMap
metadata:
  creationTimestamp: 2018-06-29T03:48:35Z
  name: coredns
  namespace: kube-system
  resourceVersion: "222"
  selfLink: /api/v1/namespaces/kube-system/configmaps/coredns
  uid: 4c8c3b17-7b4f-11e8-aaa1-0cc47a453e30

But I don't see where it's getting it's upstream dns server from. I originally deployed this k8s cluster with kube-dns, but updated to coredns when 1.11 came out. My upstream server was set as 192.168.1.18, but I need to change that now. I've checked in each host's /etc/resolv.conf, 192.168.1.18 isn't listed there, and from this configmap, I don't see it either...yet if I stop DNS on 192.168.1.18, pods stop resolving externally. Where is this IP address stored?

-- Evan R.

coredns

kubernetes

1 Answer

7/26/2018

So it seems that local dns was set to coredns

/etc/resolv.conf
nameserver 127.0.0.53

if i look at the service for dns listening on 53, I get this

kubectl describe svc kube-dns --namespace kube-system
Name:              kube-dns
Namespace:         kube-system
Labels:            k8s-app=kube-dns
                   kubernetes.io/cluster-service=true
                   kubernetes.io/name=KubeDNS
Annotations:       prometheus.io/scrape=true
Selector:          k8s-app=kube-dns
Type:              ClusterIP
IP:                10.96.0.10
Port:              dns  53/UDP
TargetPort:        53/UDP
Endpoints:         10.32.0.12:53,10.32.0.14:53

which correlates to the coredns pods..which when entered...contains the ip address

kubectl exec -it --namespace kube-system coredns-78fcdf6894-l4tph -- sh
/ # cd /etc
/etc # ls
TZ                    fstab                 logrotate.d           os-release            services
alpine-release        group                 modprobe.d            passwd                shadow
apk                   hostname              modules               periodic              shells
ca-certificates       hosts                 modules-load.d        profile               ssl
ca-certificates.conf  init.d                motd                  profile.d             sysctl.conf
conf.d                inittab               mtab                  protocols             sysctl.d
coredns               issue                 network               resolv.conf           udhcpd.conf
crontabs              localtime             opt                   securetty
/etc # cat resolv.conf
nameserver 192.168.1.18
search home

ugh. what a PITA

-- Evan R.

Source: StackOverflow

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how to see upstream server of coredns in kubernetes 1.10+?

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