Kubernetes:Pod无法解析主机名 [英] Kubernetes: Pods Can't Resolve Hostnames
问题描述
我遇到Kubernetes的问题，我的Pod无法解析主机名(例如google.com或kubernetes.default).
I am encountering an issue with Kubernetes where my pods cannot resolve hostnames (such as google.com or kubernetes.default).
我目前在OpenStack的两个CentOS7实例上运行1个主节点和1个节点.我使用kubeadm进行部署.
I currently have 1 master and 1 node running on two CentOS7 instances in OpenStack. I deployed using kubeadm.
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，以使您对我的问题有所了解.
The below outlines some verification steps to maybe give some insight into my problem.
我定义一个busybox窗格:
I define a 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:
Try to perform a DNS lookup of name google.com:
$ 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:
Try to perform a DNS lookup of name kubernetes.default:
$ 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窗格是否正在运行:
Check if my DNS pod is running:
$ 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:
Check if my DNS service is up:
$ 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终结点是否公开:
Check if DNS endpoints are exposed:
$ 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，那么Kubernetes文档指出我的Pod应该继承节点(或主节点)的DNS配置.但是，即使其中只有一行(nameserver 10.92.128.40)，旋转Pod时，我也会收到以下警告:
If I am understand correctly, the Kubernetes documentation states that my pods should inherit the DNS configurations of the node (or master?). However, even with just one line in it (nameserver 10.92.128.40), I receive the below warning when spinning up a pod:
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，在/etc/resolv.conf中只能列出很多项目.但是，上面的搜索行和我的容器中的名称服务器将从何处生成?
I understand there exists a known issue where only so many items can be listed in /etc/resolv.conf. However, where would the above search line and nameserver in my container be generated from?
最后是kube-dns容器中的日志:
$ 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.不用理会它发现了几个域名服务器，而不仅仅是我在resolv.conf中所说的域名服务器，因为我原来在域名服务器中确实有更多.我试图通过删除多余的东西来简单地做到这一点:
The dnsmasq container. Disregard that it found several more nameservers than just the one I said was in my resolv.conf, as I did have more in their originally. I attempted to simply it by removing the extras:
$ 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
和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}
我主要在此处阅读提供的文档.任何方向，见识或尝试的事情将不胜感激.
I have mostly been reading the documentation provided here. Any direction, insight or things to try would be much appreciated.
推荐答案
遇到了相同的问题.我按照此文档 dns-debugging-决议进行了检查与DNS相关的Pod，服务，端点都在运行，并且没有错误消息.最后，我发现我的 calico 服务已死.在我启动印花布服务并等待了几分钟之后，它开始工作了.
Encountered the same issue. I followed this doc dns-debugging-resolution and checked DNS related pods, services, endpoints, all was running without error messages. Finally, I found my calico service was dead. After I started calico service and waited several minutes, It worked.
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