<p>Im trying to upgrade kube cluster from Ubuntu 16 to 18. After the upgrade kube-dns pod is constantly crashing. The problem appears only on U18 if i'm rolling back to U16 everything works fine.</p>

<p>Kube version "v1.10.11"</p>

<p>kube-dns pod events:</p>

<pre><code>Events:
  Type     Reason                 Age                From                                   Message
  ----     ------                 ----               ----                                   -------
  Normal   Scheduled              28m                default-scheduler                      Successfully assigned kube-dns-75966d58fb-pqxz4 to 
  Normal   SuccessfulMountVolume  28m                kubelet,   MountVolume.SetUp succeeded for volume "kube-dns-config"
  Normal   SuccessfulMountVolume  28m                kubelet,   MountVolume.SetUp succeeded for volume "kube-dns-token-h4q66"
  Normal   Pulling                28m                kubelet,   pulling image "k8s.gcr.io/k8s-dns-kube-dns-amd64:1.14.10"
  Normal   Pulled                 28m                kubelet,   Successfully pulled image "k8s.gcr.io/k8s-dns-kube-dns-amd64:1.14.10"
  Normal   Started                28m                kubelet,   Started container
  Normal   Created                28m                kubelet,   Created container
  Normal   Pulling                28m                kubelet,   pulling image "k8s.gcr.io/k8s-dns-dnsmasq-nanny-amd64:1.14.10"
  Normal   Pulling                28m                kubelet,   pulling image "k8s.gcr.io/k8s-dns-sidecar-amd64:1.14.10"
  Normal   Pulled                 28m                kubelet,   Successfully pulled image "k8s.gcr.io/k8s-dns-dnsmasq-nanny-amd64:1.14.10"
  Normal   Created                28m                kubelet,   Created container
  Normal   Pulled                 28m                kubelet,   Successfully pulled image "k8s.gcr.io/k8s-dns-sidecar-amd64:1.14.10"
  Normal   Started                28m                kubelet,   Started container
  Normal   Created                25m (x2 over 28m)  kubelet,   Created container
  Normal   Started                25m (x2 over 28m)  kubelet,   Started container
  Normal   Killing                25m                kubelet,   Killing container with id docker://dnsmasq:Container failed liveness probe.. Container will be killed and recreated.
  Normal   Pulled                 25m                kubelet,   Container image "k8s.gcr.io/k8s-dns-dnsmasq-nanny-amd64:1.14.10" already present on machine
  Warning  Unhealthy              4m (x26 over 27m)  kubelet,   Liveness probe failed: HTTP probe failed with statuscode: 503
</code></pre>

<p>kube-dns sidecar container logs:</p>

<pre><code>kubectl logs kube-dns-75966d58fb-pqxz4 -n kube-system -c sidecar
I0809 16:31:26.768964       1 main.go:51] Version v1.14.8.3
I0809 16:31:26.769049       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:1} {Label:dnsmasq Server:127.0.0.1:53 Name:kubernetes.default.svc.cluster.local. Interval:5s Type:1}] PrometheusAddr:0.0.0.0 PrometheusPort:10054 PrometheusPath:/metrics PrometheusNamespace:kubedns})
I0809 16:31:26.769079       1 dnsprobe.go:75] Starting dnsProbe {Label:kubedns Server:127.0.0.1:10053 Name:kubernetes.default.svc.cluster.local. Interval:5s Type:1}
I0809 16:31:26.769117       1 dnsprobe.go:75] Starting dnsProbe {Label:dnsmasq Server:127.0.0.1:53 Name:kubernetes.default.svc.cluster.local. Interval:5s Type:1}
W0809 16:31:33.770594       1 server.go:64] Error getting metrics from dnsmasq: read udp 127.0.0.1:49305-&gt;127.0.0.1:53: i/o timeout
W0809 16:31:40.771166       1 server.go:64] Error getting metrics from dnsmasq: read udp 127.0.0.1:49655-&gt;127.0.0.1:53: i/o timeout
W0809 16:31:47.771773       1 server.go:64] Error getting metrics from dnsmasq: read udp 127.0.0.1:53322-&gt;127.0.0.1:53: i/o timeout
W0809 16:31:54.772386       1 server.go:64] Error getting metrics from dnsmasq: read udp 127.0.0.1:58999-&gt;127.0.0.1:53: i/o timeout
W0809 16:32:01.772972       1 server.go:64] Error getting metrics from dnsmasq: read udp 127.0.0.1:35034-&gt;127.0.0.1:53: i/o timeout
W0809 16:32:08.773540       1 server.go:64] Error getting metrics from dnsmasq: read udp 127.0.0.1:33250-&gt;127.0.0.1:53: i/o timeout
</code></pre>

<p>kube-dns dnsmasq container logs:</p>

<pre><code>kubectl logs kube-dns-75966d58fb-pqxz4 -n kube-system -c dnsmasq
I0809 16:29:51.596517       1 main.go:74] opts: {{/usr/sbin/dnsmasq [-k --cache-size=1000 --dns-forward-max=150 --no-negcache --log-facility=- --server=/cluster.local/127.0.0.1#10053 --server=/in-addr.arpa/127.0.0.1#10053 --server=/in6.arpa/127.0.0.1#10053] true} /etc/k8s/dns/dnsmasq-nanny 10000000000}
I0809 16:29:51.596679       1 nanny.go:94] Starting dnsmasq [-k --cache-size=1000 --dns-forward-max=150 --no-negcache --log-facility=- --server=/cluster.local/127.0.0.1#10053 --server=/in-addr.arpa/127.0.0.1#10053 --server=/in6.arpa/127.0.0.1#10053]
I0809 16:29:52.135179       1 nanny.go:119]
W0809 16:29:52.135211       1 nanny.go:120] Got EOF from stdout
I0809 16:29:52.135277       1 nanny.go:116] dnsmasq[20]: started, version 2.78 cachesize 1000
I0809 16:29:52.135293       1 nanny.go:116] dnsmasq[20]: 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
I0809 16:29:52.135303       1 nanny.go:116] dnsmasq[20]: using nameserver 127.0.0.1#10053 for domain in6.arpa
I0809 16:29:52.135314       1 nanny.go:116] dnsmasq[20]: using nameserver 127.0.0.1#10053 for domain in-addr.arpa
I0809 16:29:52.135323       1 nanny.go:116] dnsmasq[20]: using nameserver 127.0.0.1#10053 for domain cluster.local
I0809 16:29:52.135329       1 nanny.go:116] dnsmasq[20]: reading /etc/resolv.conf
I0809 16:29:52.135334       1 nanny.go:116] dnsmasq[20]: using nameserver 127.0.0.1#10053 for domain in6.arpa
I0809 16:29:52.135343       1 nanny.go:116] dnsmasq[20]: using nameserver 127.0.0.1#10053 for domain in-addr.arpa
I0809 16:29:52.135348       1 nanny.go:116] dnsmasq[20]: using nameserver 127.0.0.1#10053 for domain cluster.local
I0809 16:29:52.135353       1 nanny.go:116] dnsmasq[20]: using nameserver 127.0.0.53#53
I0809 16:29:52.135397       1 nanny.go:116] dnsmasq[20]: read /etc/hosts - 7 addresses
I0809 16:31:28.728897       1 nanny.go:116] dnsmasq[20]: Maximum number of concurrent DNS queries reached (max: 150)
I0809 16:31:38.746899       1 nanny.go:116] dnsmasq[20]: Maximum number of concurrent DNS queries reached (max: 150)
</code></pre>

<p>I have deleted the existing pods but newly created getting same error after some time. Not sure why this is happening only on Ubuntu 18. Any ideas how to fix this?</p>

DenisTs
<p>In my case i have found that in ubuntu18 the resolve.conf was pointing pointing to: <code>/etc/resolv.conf -&gt; ../run/systemd/resolve/stub-resolv.conf</code>
and it had <code>nameserver 127.0.0.53</code> entry.
At the same time under /run/systemd/resolve  you should have another resolv.conf</p>

<pre><code>/run/systemd/resolve$ ll
total 8
drwxr-xr-x  2 systemd-resolve systemd-resolve  80 Aug  12 13:24 ./
drwxr-xr-x 23 root            root            520 Aug  12 11:54 ../
-rw-r--r--  1 systemd-resolve systemd-resolve 607 Aug  12 13:24 resolv.conf
-rw-r--r--  1 systemd-resolve systemd-resolve 735 Aug  12 13:24 stub-resolv.conf
</code></pre>

<p>In my case resolv.conf contains private IP nameserver 172.27.0.2.
Just relink to the ../run/systemd/resolve/resolv.conf on all cluster machines and reboot the kube-dns pods.</p>
