我遇到了Kubernetes的问题，我的pod无法解析主机名（例如google.com或kubernetes.default）。
我目前在OpenStack中的两个CentOS7实例上运行了1个主节点和1个节点。我使用kubeadm进行了部署。
以下是安装的版本：
kubeadm-1.7.3-1.x86_64
kubectl-1.7.3-1.x86_64
kubelet-1.7.3-1.x86_64
kubernetes-cni-0.5.1-0.x86_64
下面概述了一些验证步骤，可能会对我的问题有所了解。
我定义了一个busybox pod：
apiVersion: v1
kind: Pod
metadata:
name: busybox
namespace: default
spec:
containers:
- image: busybox
command:
- sleep
- "3600"
imagePullPolicy: IfNotPresent
name: busybox
restartPolicy: Always
然后创建pod：
$ kubectl create -f busybox.yaml
尝试执行名称为google.com的DNS查找：
$ kubectl exec -ti busybox -- nslookup google.com
Server: 10.96.0.10
Address 1: 10.96.0.10
nslookup: can't resolve 'google.com'
尝试执行名称为kubernetes.default的DNS查找：
$ kubectl exec -ti busybox -- nslookup kubernetes.default
Server: 10.96.0.10
Address 1: 10.96.0.10
nslookup: can't resolve 'kubernetes.default'
检查我的DNS pod是否正在运行：
$ kubectl get pods --namespace=kube-system -l k8s-app=kube-dns
NAME READY STATUS RESTARTS AGE
kube-dns-2425271678-k1nft 3/3 Running 9 5d
检查我的DNS服务是否已启动：
$ kubectl get svc --namespace=kube-system
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kube-dns 10.96.0.10 <none> 53/UDP,53/TCP 5d
检查DNS端点是否暴露：
$ kubectl get ep kube-dns --namespace=kube-system
NAME ENDPOINTS AGE
kube-dns 10.244.0.5:53,10.244.0.5:53 5d
检查我容器中/etc/resolv.conf的内容：
$ kubectl exec -ti busybox -- cat /etc/resolv.conf
nameserver 10.96.0.10
search default.svc.cluster.local svc.cluster.local cluster.local
options ndots:5
如果我理解正确，Kubernetes文档说明我的pod应该继承节点（或master？）的DNS配置。但是，即使只有一行（nameserver 10.92.128.40），我在旋转播放时会收到以下警告：
Search Line limits were exceeded, some dns names have been omitted, the applied search line is: default.svc.cluster.local svc.cluster.local cluster.local mydomain.net anotherdomain.net yetanotherdomain.net
我知道存在一个已知问题，/etc/resolv.conf中只能列出这么多项目。但是，我的容器中的上述搜索行和名称服务器将从哪里生成？
最后，这是来自kube-dns容器的日志：
$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c kubedns
I0817 20:54:58.445280 1 dns.go:48] version: 1.14.3-4-gee838f6
I0817 20:54:58.452551 1 server.go:70] Using configuration read from directory: /kube-dns-config with period 10s
I0817 20:54:58.452616 1 server.go:113] FLAG: --alsologtostderr="false"
I0817 20:54:58.452628 1 server.go:113] FLAG: --config-dir="/kube-dns-config"
I0817 20:54:58.452638 1 server.go:113] FLAG: --config-map=""
I0817 20:54:58.452643 1 server.go:113] FLAG: --config-map-namespace="kube-system"
I0817 20:54:58.452650 1 server.go:113] FLAG: --config-period="10s"
I0817 20:54:58.452659 1 server.go:113] FLAG: --dns-bind-address="0.0.0.0"
I0817 20:54:58.452665 1 server.go:113] FLAG: --dns-port="10053"
I0817 20:54:58.452674 1 server.go:113] FLAG: --domain="cluster.local."
I0817 20:54:58.452683 1 server.go:113] FLAG: --federations=""
I0817 20:54:58.452692 1 server.go:113] FLAG: --healthz-port="8081"
I0817 20:54:58.452698 1 server.go:113] FLAG: --initial-sync-timeout="1m0s"
I0817 20:54:58.452704 1 server.go:113] FLAG: --kube-master-url=""
I0817 20:54:58.452713 1 server.go:113] FLAG: --kubecfg-file=""
I0817 20:54:58.452718 1 server.go:113] FLAG: --log-backtrace-at=":0"
I0817 20:54:58.452727 1 server.go:113] FLAG: --log-dir=""
I0817 20:54:58.452734 1 server.go:113] FLAG: --log-flush-frequency="5s"
I0817 20:54:58.452741 1 server.go:113] FLAG: --logtostderr="true"
I0817 20:54:58.452746 1 server.go:113] FLAG: --nameservers=""
I0817 20:54:58.452752 1 server.go:113] FLAG: --stderrthreshold="2"
I0817 20:54:58.452759 1 server.go:113] FLAG: --v="2"
I0817 20:54:58.452765 1 server.go:113] FLAG: --version="false"
I0817 20:54:58.452775 1 server.go:113] FLAG: --vmodule=""
I0817 20:54:58.452856 1 server.go:176] Starting SkyDNS server (0.0.0.0:10053)
I0817 20:54:58.453680 1 server.go:198] Skydns metrics enabled (/metrics:10055)
I0817 20:54:58.453692 1 dns.go:147] Starting endpointsController
I0817 20:54:58.453699 1 dns.go:150] Starting serviceController
I0817 20:54:58.453841 1 logs.go:41] skydns: ready for queries on cluster.local. for tcp://0.0.0.0:10053 [rcache 0]
I0817 20:54:58.453852 1 logs.go:41] skydns: ready for queries on cluster.local. for udp://0.0.0.0:10053 [rcache 0]
I0817 20:54:58.964468 1 dns.go:171] Initialized services and endpoints from apiserver
I0817 20:54:58.964523 1 server.go:129] Setting up Healthz Handler (/readiness)
I0817 20:54:58.964536 1 server.go:134] Setting up cache handler (/cache)
I0817 20:54:58.964545 1 server.go:120] Status HTTP port 8081
dnsmasq容器。无视它发现了几个名字服务器而不仅仅是我所说的resolv.conf中的名字服务器，因为我原来的确有更多。我试图通过删除附加内容来简单地使用它：
$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c dnsmasq
I0817 20:55:03.295826 1 main.go:76] opts: {{/usr/sbin/dnsmasq [-k --cache-size=1000 --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}
I0817 20:55:03.298134 1 nanny.go:86] Starting dnsmasq [-k --cache-size=1000 --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]
I0817 20:55:03.731577 1 nanny.go:111]
W0817 20:55:03.731609 1 nanny.go:112] Got EOF from stdout
I0817 20:55:03.731642 1 nanny.go:108] dnsmasq[9]: started, version 2.76 cachesize 1000
I0817 20:55:03.731656 1 nanny.go:108] dnsmasq[9]: 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
I0817 20:55:03.731681 1 nanny.go:108] dnsmasq[9]: using nameserver 127.0.0.1#10053 for domain ip6.arpa
I0817 20:55:03.731689 1 nanny.go:108] dnsmasq[9]: using nameserver 127.0.0.1#10053 for domain in-addr.arpa
I0817 20:55:03.731695 1 nanny.go:108] dnsmasq[9]: using nameserver 127.0.0.1#10053 for domain cluster.local
I0817 20:55:03.731704 1 nanny.go:108] dnsmasq[9]: reading /etc/resolv.conf
I0817 20:55:03.731710 1 nanny.go:108] dnsmasq[9]: using nameserver 127.0.0.1#10053 for domain ip6.arpa
I0817 20:55:03.731717 1 nanny.go:108] dnsmasq[9]: using nameserver 127.0.0.1#10053 for domain in-addr.arpa
I0817 20:55:03.731723 1 nanny.go:108] dnsmasq[9]: using nameserver 127.0.0.1#10053 for domain cluster.local
I0817 20:55:03.731729 1 nanny.go:108] dnsmasq[9]: using nameserver 10.92.128.40#53
I0817 20:55:03.731735 1 nanny.go:108] dnsmasq[9]: using nameserver 10.92.128.41#53
I0817 20:55:03.731741 1 nanny.go:108] dnsmasq[9]: using nameserver 10.95.207.66#53
I0817 20:55:03.731747 1 nanny.go:108] dnsmasq[9]: read /etc/hosts - 7 addresses
sidecar容器：
$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c sidecar
ERROR: logging before flag.Parse: I0817 20:55:04.488391 1 main.go:48] Version v1.14.3-4-gee838f6
ERROR: logging before flag.Parse: I0817 20:55:04.488612 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})
ERROR: logging before flag.Parse: I0817 20:55:04.488667 1 dnsprobe.go:75] Starting dnsProbe {Label:kubedns Server:127.0.0.1:10053 Name:kubernetes.default.svc.cluster.local. Interval:5s Type:1}
ERROR: logging before flag.Parse: I0817 20:55:04.488766 1 dnsprobe.go:75] Starting dnsProbe {Label:dnsmasq Server:127.0.0.1:53 Name:kubernetes.default.svc.cluster.local. Interval:5s Type:1}
我大部分时间都在阅读group join提供的文件。任何方向，见解或尝试的事情都将非常感激。
答案 0 :(得分：5)
我有类似的问题。重新启动coredns部署为我解决了这个问题：
kubectl -n kube-system rollout restart deployment coredns
答案 1 :(得分：3)
有些想法浮现在脑海中：
答案 2 :(得分：3)
遇到同样的问题。我遵循了该文档dns-debugging-resolution，并检查了与DNS相关的Pod，服务，端点，它们都在运行，并且没有错误消息。最终，我发现我的 calico 服务已终止。在我启动印花布服务并等待了几分钟后，它开始工作。
答案 3 :(得分：1)
如果发现类似以下错误，请检查coredns pods日志：
# kubectl logs --namespace=kube-system coredns-XXX
...
[ERROR] plugin/errors ... HINFO: read udp ... read: no route to host
然后确保主机上启用了防火墙化装：
# firewall-cmd --list-all
...
masquerade: yes
Enable if it's "no":
# firewall-cmd --add-masquerade --permanent
# firewall-cmd --reload
*此后您可能需要重新启动/重启