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Question

Kubernetes not working with DNS - no communication from pod to outside world

4/18/2018

I have probaly problem with kubernetes DNS as my service cannot communicate to outside world (bitbucker.org). Actually I found this page: https://kubernetes.io/docs/tasks/administer-cluster/dns-debugging-resolution/

and validate it on my cluster (no minikube):

zordon@megazord:~$ kubectl exec busybox cat /etc/resolv.conf
nameserver 10.96.0.10
search default.svc.cluster.local svc.cluster.local cluster.local
options ndots:5

and:

zordon@megazord:~$ kubectl exec -ti busybox -- nslookup kubernetes.default
Server:    10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local

nslookup: can't resolve 'kubernetes.default'
command terminated with exit code 1

Any idea how can I resolve to be able connect from inside pod to outside world ?

This probably is related to Flannel, as connectivity from image run only by docker is avalible. Whant to mention that I have run my cluster with this example: https://blog.alexellis.io/kubernetes-in-10-minutes/

I have also modify https://github.com/coreos/flannel/blob/master/Documentation/kube-flannel.yml and pass argument --iface with my wifi card which has acces to internet but then kube-flannel-ds cannot start from:

args:
        - --ip-masq
        - --kube-subnet-mgr

to:

args:
        - --ip-masq
        - --kube-subnet-mgr
        - --iface=wlan0ec5


zordon@megazord:~$ kubectl get pods  -n kube-system
NAME                               READY     STATUS    RESTARTS   AGE
etcd-megazord                      1/1       Running   1          21m
kube-apiserver-megazord            1/1       Running   1          21m
kube-controller-manager-megazord   1/1       Running   1          22m
kube-dns-86f4d74b45-8gh6q          3/3       Running   5          22m
kube-flannel-ds-2wqqr              1/1       Running   1          17m
kube-flannel-ds-59txb              1/1       Running   1          15m
kube-proxy-bdxb4                   1/1       Running   1          15m
kube-proxy-mg44x                   1/1       Running   1          22m
kube-scheduler-megazord            1/1       Running   1          22m


zordon@megazord:~$ kubectl get svc  -n kube-system
NAME       TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)         AGE
kube-dns   ClusterIP   10.96.0.10   <none>        53/UDP,53/TCP   23m

zordon@megazord:~$ kubectl describe service kube-dns -n kube-system
Name:              kube-dns
Namespace:         kube-system
Labels:            k8s-app=kube-dns
                   kubernetes.io/cluster-service=true
                   kubernetes.io/name=KubeDNS
Annotations:       <none>
Selector:          k8s-app=kube-dns
Type:              ClusterIP
IP:                10.96.0.10
Port:              dns  53/UDP
TargetPort:        53/UDP
Endpoints:         10.244.0.27:53
Port:              dns-tcp  53/TCP
TargetPort:        53/TCP
Endpoints:         10.244.0.27:53
Session Affinity:  None
Events:            <none>

zordon@megazord:~$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c kubedns
I0419 17:40:11.473047       1 dns.go:48] version: 1.14.8
I0419 17:40:11.473975       1 server.go:71] Using configuration read from directory: /kube-dns-config with period 10s
I0419 17:40:11.474024       1 server.go:119] FLAG: --alsologtostderr="false"
I0419 17:40:11.474032       1 server.go:119] FLAG: --config-dir="/kube-dns-config"
I0419 17:40:11.474037       1 server.go:119] FLAG: --config-map=""
I0419 17:40:11.474041       1 server.go:119] FLAG: --config-map-namespace="kube-system"
I0419 17:40:11.474044       1 server.go:119] FLAG: --config-period="10s"
I0419 17:40:11.474049       1 server.go:119] FLAG: --dns-bind-address="0.0.0.0"
I0419 17:40:11.474053       1 server.go:119] FLAG: --dns-port="10053"
I0419 17:40:11.474058       1 server.go:119] FLAG: --domain="cluster.local."
I0419 17:40:11.474063       1 server.go:119] FLAG: --federations=""
I0419 17:40:11.474067       1 server.go:119] FLAG: --healthz-port="8081"
I0419 17:40:11.474071       1 server.go:119] FLAG: --initial-sync-timeout="1m0s"
I0419 17:40:11.474074       1 server.go:119] FLAG: --kube-master-url=""
I0419 17:40:11.474079       1 server.go:119] FLAG: --kubecfg-file=""
I0419 17:40:11.474082       1 server.go:119] FLAG: --log-backtrace-at=":0"
I0419 17:40:11.474087       1 server.go:119] FLAG: --log-dir=""
I0419 17:40:11.474091       1 server.go:119] FLAG: --log-flush-frequency="5s"
I0419 17:40:11.474094       1 server.go:119] FLAG: --logtostderr="true"
I0419 17:40:11.474098       1 server.go:119] FLAG: --nameservers=""
I0419 17:40:11.474101       1 server.go:119] FLAG: --stderrthreshold="2"
I0419 17:40:11.474104       1 server.go:119] FLAG: --v="2"
I0419 17:40:11.474107       1 server.go:119] FLAG: --version="false"
I0419 17:40:11.474113       1 server.go:119] FLAG: --vmodule=""
I0419 17:40:11.474190       1 server.go:201] Starting SkyDNS server (0.0.0.0:10053)
I0419 17:40:11.488125       1 server.go:220] Skydns metrics enabled (/metrics:10055)
I0419 17:40:11.488170       1 dns.go:146] Starting endpointsController
I0419 17:40:11.488180       1 dns.go:149] Starting serviceController
I0419 17:40:11.488348       1 logs.go:41] skydns: ready for queries on cluster.local. for tcp://0.0.0.0:10053 [rcache 0]
I0419 17:40:11.488407       1 logs.go:41] skydns: ready for queries on cluster.local. for udp://0.0.0.0:10053 [rcache 0]
I0419 17:40:11.988549       1 dns.go:170] Initialized services and endpoints from apiserver
I0419 17:40:11.988609       1 server.go:135] Setting up Healthz Handler (/readiness)
I0419 17:40:11.988641       1 server.go:140] Setting up cache handler (/cache)
I0419 17:40:11.988649       1 server.go:126] Status HTTP port 8081


zordon@megazord:~$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c dnsmasq
I0419 17:44:35.785171       1 main.go:76] opts: {{/usr/sbin/dnsmasq [-k --cache-size=1000 --no-negcache --log-facility=- --server=/cluster.local/127.0.0.1#10053 --server=/in-addr.arpa/127.0.0.1#10053 --server=/ip6.arpa/127.0.0.1#10053] true} /etc/k8s/dns/dnsmasq-nanny 10000000000}
I0419 17:44:35.785336       1 nanny.go:94] Starting dnsmasq [-k --cache-size=1000 --no-negcache --log-facility=- --server=/cluster.local/127.0.0.1#10053 --server=/in-addr.arpa/127.0.0.1#10053 --server=/ip6.arpa/127.0.0.1#10053]
I0419 17:44:35.876534       1 nanny.go:119]
W0419 17:44:35.876572       1 nanny.go:120] Got EOF from stdout
I0419 17:44:35.876578       1 nanny.go:116] dnsmasq[26]: started, version 2.78 cachesize 1000
I0419 17:44:35.876615       1 nanny.go:116] dnsmasq[26]: compile time options: IPv6 GNU-getopt no-DBus no-i18n no-IDN DHCP DHCPv6 no-Lua TFTP no-conntrack ipset auth no-DNSSEC loop-detect inotify
I0419 17:44:35.876632       1 nanny.go:116] dnsmasq[26]: using nameserver 127.0.0.1#10053 for domain ip6.arpa
I0419 17:44:35.876642       1 nanny.go:116] dnsmasq[26]: using nameserver 127.0.0.1#10053 for domain in-addr.arpa
I0419 17:44:35.876653       1 nanny.go:116] dnsmasq[26]: using nameserver 127.0.0.1#10053 for domain cluster.local
I0419 17:44:35.876666       1 nanny.go:116] dnsmasq[26]: reading /etc/resolv.conf
I0419 17:44:35.876677       1 nanny.go:116] dnsmasq[26]: using nameserver 127.0.0.1#10053 for domain ip6.arpa
I0419 17:44:35.876691       1 nanny.go:116] dnsmasq[26]: using nameserver 127.0.0.1#10053 for domain in-addr.arpa
I0419 17:44:35.876701       1 nanny.go:116] dnsmasq[26]: using nameserver 127.0.0.1#10053 for domain cluster.local
I0419 17:44:35.876709       1 nanny.go:116] dnsmasq[26]: using nameserver 127.0.0.53#53
I0419 17:44:35.876717       1 nanny.go:116] dnsmasq[26]: read /etc/hosts - 7 addresses

**zordon@megazord:~$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c sidecar**
I0419 17:45:06.726670       1 main.go:51] Version v1.14.8
I0419 17:45:06.726781       1 server.go:45] Starting server (options {DnsMasqPort:53 DnsMasqAddr:127.0.0.1 DnsMasqPollIntervalMs:5000 Probes:[{Label:kubedns Server:127.0.0.1:10053 Name:kubernetes.default.svc.cluster.local. Interval:5s Type:33} {Label:dnsmasq Server:127.0.0.1:53 Name:kubernetes.default.svc.cluster.local. Interval:5s Type:33}] PrometheusAddr:0.0.0.0 PrometheusPort:10054 PrometheusPath:/metrics PrometheusNamespace:kubedns})
I0419 17:45:06.726842       1 dnsprobe.go:75] Starting dnsProbe {Label:kubedns Server:127.0.0.1:10053 Name:kubernetes.default.svc.cluster.local. Interval:5s Type:33}
I0419 17:45:06.726927       1 dnsprobe.go:75] Starting dnsProbe {Label:dnsmasq Server:127.0.0.1:53 Name:kubernetes.default.svc.cluster.local. Interval:5s Type:33}

Master node:

zordon@megazord:~$ ip -d route
unicast default via 192.168.1.1 dev wlp32s0 proto static scope global metric 600
unicast 10.244.0.0/24 dev cni0 proto kernel scope link src 10.244.0.1
unicast 10.244.1.0/24 via 10.244.1.0 dev flannel.1 proto boot scope global onlink
unicast 169.254.0.0/16 dev wlp32s0 proto boot scope link metric 1000
unicast 172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1
unicast 192.168.1.0/24 dev wlp32s0 proto kernel scope link src 192.168.1.110 metric 600
zordon@megazord:~$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp30s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether 4c:cc:6a:f8:7e:4b brd ff:ff:ff:ff:ff:ff
3: wlp32s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether ec:08:6b:0c:9c:27 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.110/24 brd 192.168.1.255 scope global wlp32s0
       valid_lft forever preferred_lft forever
    inet6 fe80::f632:2f08:9caa:2c82/64 scope link
       valid_lft forever preferred_lft forever
4: docker0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
    link/ether 02:42:32:19:f7:5a brd ff:ff:ff:ff:ff:ff
    inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
       valid_lft forever preferred_lft forever
    inet6 fe80::42:32ff:fe19:f75a/64 scope link
       valid_lft forever preferred_lft forever
6: vethf9de74d@if5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master docker0 state UP group default
    link/ether ba:af:58:a0:4a:74 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet6 fe80::b8af:58ff:fea0:4a74/64 scope link
       valid_lft forever preferred_lft forever
7: flannel.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UNKNOWN group default
    link/ether a6:d1:45:73:c3:31 brd ff:ff:ff:ff:ff:ff
    inet 10.244.0.0/32 scope global flannel.1
       valid_lft forever preferred_lft forever
    inet6 fe80::a4d1:45ff:fe73:c331/64 scope link
       valid_lft forever preferred_lft forever
8: cni0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UP group default qlen 1000
    link/ether 0a:58:0a:f4:00:01 brd ff:ff:ff:ff:ff:ff
    inet 10.244.0.1/24 scope global cni0
       valid_lft forever preferred_lft forever
    inet6 fe80::24f5:4cff:fee9:a32d/64 scope link
       valid_lft forever preferred_lft forever
9: veth58367f89@if3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue master cni0 state UP group default
    link/ether 7a:29:e9:c8:bf:3f brd ff:ff:ff:ff:ff:ff link-netnsid 1
    inet6 fe80::7829:e9ff:fec8:bf3f/64 scope link
       valid_lft forever preferred_lft forever

Node worker:

zordon@k8s-minion-one:~$ ip -d route
unicast default via 192.168.1.1 dev enp0s25 proto dhcp scope global src 192.168.1.111 metric 100
unicast 10.244.0.0/24 via 10.244.0.0 dev flannel.1 proto boot scope global onlink
unicast 10.244.1.0/24 dev cni0 proto kernel scope link src 10.244.1.1 linkdown
unicast 172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1 linkdown
unicast 192.168.1.0/24 dev enp0s25 proto kernel scope link src 192.168.1.111
unicast 192.168.1.1 dev enp0s25 proto dhcp scope link src 192.168.1.111 metric 100
zordon@k8s-minion-one:~$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 18:03:73:45:75:71 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.111/24 brd 192.168.1.255 scope global enp0s25
       valid_lft forever preferred_lft forever
    inet6 fe80::1a03:73ff:fe45:7571/64 scope link
       valid_lft forever preferred_lft forever
3: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
    link/ether 02:42:38:3e:a3:94 brd ff:ff:ff:ff:ff:ff
    inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
       valid_lft forever preferred_lft forever
    inet6 fe80::42:38ff:fe3e:a394/64 scope link
       valid_lft forever preferred_lft forever
4: flannel.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UNKNOWN group default
    link/ether 7a:d0:2a:b4:73:43 brd ff:ff:ff:ff:ff:ff
    inet 10.244.1.0/32 scope global flannel.1
       valid_lft forever preferred_lft forever
    inet6 fe80::78d0:2aff:feb4:7343/64 scope link
       valid_lft forever preferred_lft forever
5: cni0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
    link/ether 0a:58:0a:f4:01:01 brd ff:ff:ff:ff:ff:ff
    inet 10.244.1.1/24 scope global cni0
       valid_lft forever preferred_lft forever
    inet6 fe80::7440:12ff:fefa:f55/64 scope link
       valid_lft forever preferred_lft forever

-- lukisp

dns

kubernetes

2 Answers

4/19/2018

It's definitely related to flannel subsystem. But prior to debugging flannel, it would be useful to know what is happening with the kube-dns pod.

Try to check kube-dns pods and service status using commands:

ensure all pods state is 1/1 or 3/3 for kube-dns pod

$ kubectl get pods  -n kube-system
NAME                                   READY     STATUS    RESTARTS   AGE
etcd-kube-flannel                      1/1       Running   0          41m
kube-apiserver-kube-flannel            1/1       Running   0          41m
kube-controller-manager-kube-flannel   1/1       Running   0          41m
kube-dns-86f4d74b45-569vs              3/3       Running   0          42m
kube-flannel-ds-j482l                  1/1       Running   0          38m
kube-proxy-4jjjz                       1/1       Running   0          42m
kube-scheduler-kube-flannel            1/1       Running   0          41m

check service state

$ kubectl get svc  -n kube-system
NAME       TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)         AGE
kube-dns   ClusterIP   10.96.0.10   <none>        53/UDP,53/TCP   42m

check service details

$ kubectl describe service kube-dns -n kube-system
Name:              kube-dns
Namespace:         kube-system
Labels:            k8s-app=kube-dns
                   kubernetes.io/cluster-service=true
                   kubernetes.io/name=KubeDNS
Annotations:       <none>
Selector:          k8s-app=kube-dns
Type:              ClusterIP
IP:                10.96.0.10
Port:              dns  53/UDP
TargetPort:        53/UDP
Endpoints:         10.244.0.2:53
Port:              dns-tcp  53/TCP
TargetPort:        53/TCP
Endpoints:         10.244.0.2:53
Session Affinity:  None
Events:            <none>

Check kube-dns logs as mentioned in Debugging DNS Resolution:

$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c kubedns
$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c dnsmasq
$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c sidecar

Last command gives you a health check status of kube-dns pod.

This should be enough to understand what has been broken.

-- VAS

Source: StackOverflow

4/23/2018

I found the problem. Problem occures when i deploy busybox and try to ping external serwer with name. Problem not exists when I used IP address. So the problem whas in DNS and name resolving. during ping I look into dns logs and see the problem. Helped me config map for dn:

apiVersion: v1
kind: ConfigMap
metadata:
  name: kube-dns
  namespace: kube-system
  labels:
    addonmanager.kubernetes.io/mode: EnsureExists
data:
  upstreamNameservers: |-
    ["8.8.8.8", "8.8.4.4"]

-- lukisp

Source: StackOverflow

KQ

Kubernetes not working with DNS - no communication from pod to outside world

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