Kubernetes：无法从 Pod 中解析主机名

Question

Kubernetes新手，但在过去使用过K3s。只需设置一个K8s集群。我的pod都不能做DNS查找，即使是谷歌，或内部域。

I init'd with:--pod-network-cidr=10.244.0.0/16。安装了Metal-LB(10.7.7.10-10.7.7.254)，节点和master运行ip为10.7.50。X/16和10.7.60。X/16分别。使用默认的Kube-Flannel设置法兰绒:https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml

到目前为止，它只是一个主节点和两个节点。

版本:

$ kubeadm version
kubeadm version: &version.Info{Major:"1", Minor:"22", GitVersion:"v1.22.1", GitCommit:"632ed300f2c34f6d6d15ca4cef3d3c7073412212", GitTreeState:"clean", BuildDate:"2021-08-19T15:44:22Z", GoVersion:"go1.16.7", Compiler:"gc", Platform:"linux/amd64"}
$ kubectl version
Client Version: version.Info{Major:"1", Minor:"22", GitVersion:"v1.22.1", GitCommit:"632ed300f2c34f6d6d15ca4cef3d3c7073412212", GitTreeState:"clean", BuildDate:"2021-08-19T15:45:37Z", GoVersion:"go1.16.7", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"22", GitVersion:"v1.22.1", GitCommit:"632ed300f2c34f6d6d15ca4cef3d3c7073412212", GitTreeState:"clean", BuildDate:"2021-08-19T15:39:34Z", GoVersion:"go1.16.7", Compiler:"gc", Platform:"linux/amd64"}
$ kubelet --version
Kubernetes v1.22.1

故障排除命令:

$ 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=CoreDNS
Annotations:       prometheus.io/port: 9153
prometheus.io/scrape: true
Selector:          k8s-app=kube-dns
Type:              ClusterIP
IP Family Policy:  SingleStack
IP Families:       IPv4
IP:                10.96.0.10
IPs:               10.96.0.10
Port:              dns  53/UDP
TargetPort:        53/UDP
Endpoints:         10.244.1.20:53,10.244.2.28:53
Port:              dns-tcp  53/TCP
TargetPort:        53/TCP
Endpoints:         10.244.1.20:53,10.244.2.28:53
Port:              metrics  9153/TCP
TargetPort:        9153/TCP
Endpoints:         10.244.1.20:9153,10.244.2.28:9153
Session Affinity:  None
Events:            <none>

$ kubectl get pods -n kube-system -o wide
NAME                              READY   STATUS    RESTARTS       AGE     IP            NODE      NOMINATED NODE   READINESS GATES
coredns-84f8874d6d-jgvwk          1/1     Running   1 (115m ago)   21h     10.244.1.20   k-w-001   <none>           <none>
coredns-84f8874d6d-qh2f4          1/1     Running   1 (115m ago)   21h     10.244.2.28   k-w-002   <none>           <none>
etcd-k-m-001                      1/1     Running   12 (15m ago)   2d22h   10.7.50.11    k-m-001   <none>           <none>
kube-apiserver-k-m-001            1/1     Running   11 (15m ago)   2d22h   10.7.50.11    k-m-001   <none>           <none>
kube-controller-manager-k-m-001   1/1     Running   12 (15m ago)   2d22h   10.7.50.11    k-m-001   <none>           <none>
kube-flannel-ds-286dc             1/1     Running   10 (15m ago)   2d22h   10.7.50.11    k-m-001   <none>           <none>
kube-flannel-ds-rbmhx             1/1     Running   6 (114m ago)   2d21h   10.7.60.11    k-w-001   <none>           <none>
kube-flannel-ds-vjl7l             1/1     Running   4 (115m ago)   2d21h   10.7.60.12    k-w-002   <none>           <none>
kube-proxy-948z8                  1/1     Running   8 (15m ago)    2d22h   10.7.50.11    k-m-001   <none>           <none>
kube-proxy-l7h64                  1/1     Running   4 (115m ago)   2d21h   10.7.60.12    k-w-002   <none>           <none>
kube-proxy-pqmsr                  1/1     Running   4 (115m ago)   2d21h   10.7.60.11    k-w-001   <none>           <none>
kube-scheduler-k-m-001            1/1     Running   12 (15m ago)   2d22h   10.7.50.11    k-m-001   <none>           <none>
metrics-server-6dfddc5fb8-47mnb   0/1     Running   3 (115m ago)   2d20h   10.244.1.21   k-w-001   <none>           <none>

$ kubectl logs --namespace=kube-system coredns-84f8874d6d-jgvwk
.:53
[INFO] plugin/reload: Running configuration MD5 = db32ca3650231d74073ff4cf814959a7
CoreDNS-1.8.4
linux/amd64, go1.16.4, 053c4d5
$ kubectl logs --namespace=kube-system coredns-84f8874d6d-qh2f4
[INFO] plugin/ready: Still waiting on: "kubernetes"
.:53
[INFO] plugin/reload: Running configuration MD5 = db32ca3650231d74073ff4cf814959a7
CoreDNS-1.8.4
linux/amd64, go1.16.4, 053c4d5

每隔几秒进行一次测试:

$ kubectl exec -ti busybox -- nslookup kubernetes.default
Server:         10.96.0.10
Address:        10.96.0.10:53
*** Can't find kubernetes.default: No answer
*** Can't find kubernetes.default: No answer
$ kubectl exec -ti busybox -- nslookup kubernetes.default
;; connection timed out; no servers could be reached
command terminated with exit code 1

这里有更多的测试:

$ kubectl exec -ti busybox -- nslookup google.com
;; connection timed out; no servers could be reached
command terminated with exit code 1
$ kubectl exec -ti busybox -- nslookup google.com 8.8.8.8
Server:         8.8.8.8
Address:        8.8.8.8:53
Non-authoritative answer:
Name:   google.com
Address: 142.251.33.78
*** Can't find google.com: No answer
$ kubectl exec -ti busybox -- ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8): 56 data bytes
64 bytes from 8.8.8.8: seq=0 ttl=116 time=6.437 ms
$ 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
$ kubectl exec -ti busybox -- nslookup kubernetes.default  10.96.0.10
Server:         10.96.0.10
Address:        10.96.0.10:53
*** Can't find kubernetes.default: No answer
*** Can't find kubernetes.default: No answer
$ kubectl exec -ti busybox -- nslookup kubernetes.default 10.96.0.10
;; connection timed out; no servers could be reached
command terminated with exit code 1

我还注意到kube-dns服务将应用程序选择器设置为k8s-app=kube-dns，而coredns具有标签k8s-app=kube-dns，这是正确的吗?

在kube-system名称空间中运行的pod似乎有两个不同的IP范围。一个使用Node的IP，另一个使用Flannels。

我不确定这里发生了什么，对Kubernetes来说是新的，但看起来DNS pod或服务根本不工作。

编辑:

进一步信息:

$ sudo ufw status
Status: inactive

Answer 1

问题实际上是法兰绒。DNS查询工作正常，直到节点重新启动，然后所有pod查询失败，直到Flannel pod重新启动。

天哪，这是一个兔子洞。

见:https://github.com/flannel-io/flannel/issues/1321