关于k8s解析不到pod dns信息 - 好文

<>关于k8s解析不到pod dns信息

这其实是自己对k8s的dns解析不理解，service和pod在k8s中的dns记录形式不同，
service是通过名字的，pod是用ip的（192-168-0-1的形式）。但是，通过pod-ip访问，很傻，已经知道ip,那还查什么，于是乎，又有了
pod-hostname.subdomain.ns.cluster.local的方式；需要在pod spec中配置 hostname和subdomain。

官网demo使用headless-svc，实际上用其他svc也可以，文末用clusterIP的svc演示。

* busybox:1.28，latest版本不行 apiVersion: v1 kind: Service metadata: name:
default-subdomain spec: selector: name: busybox clusterIP: None ports: - name:
foo# Actually, no port is needed. port: 1234 targetPort: 1234 --- apiVersion:
v1 kind: Pod metadata: name: busybox1 labels: name: busybox spec: hostname:
busybox-1 subdomain: default-subdomain containers: - image: busybox:1.28
command: -sleep - "3600" name: busybox --- apiVersion: v1 kind: Pod metadata:
name: busybox2 labels: name: busybox spec: hostname: busybox-2 subdomain:
default-subdomain containers: - image: busybox:1.28 command: -sleep - "3600"
name: busybox
* service [root@cce-demo1522483688765-00274 cka]# kubectl get svc NAME TYPE
CLUSTER-IP EXTERNAL-IP PORT(S) AGE http ClusterIP 10.247.44.63 <none> 8080/TCP
3d kubernetes ClusterIP 10.247.0.1<none> 443/TCP 3d mydb ClusterIP 10.247.6.172
<none> 80/TCP 2h myservice ClusterIP 10.247.148.200 <none> 80/TCP 2h [
root@cce-demo1522483688765-00274 cka]# kubectl exec -it busybox1 -- nslookup
http Server: 10.247.3.10 Address 1: 10.247.3.10
kube-dns.kube-system.svc.cluster.local Name: http Address 1: 10.247.44.63
http.default.svc.cluster.local[root@cce-demo1522483688765-00274 cka]#
* pod [root@cce-demo1522483688765-00274 cka]# kubectl get pods -owide NAME
READY STATUS RESTARTS AGE IP NODE busybox1 1/1 Running 0 28m 172.16.0.32
192.168.0.151 busybox2 1/1 Running 0 21m 172.16.0.26 192.168.0.151 counter 1/1
Running 0 1h 172.16.0.22 192.168.0.151 http-7767dd48cf-cpthr 1/1 Running 0 1d
172.16.0.31 192.168.0.151 http-7767dd48cf-f5mfd 1/1 Running 0 1d 172.16.0.29
192.168.0.151 http2-fbb647ddf-gv267 1/1 Running 0 1d 172.16.0.30 192.168.0.151
myapp-pod2 1/1 Running 2 2h 172.16.0.16 192.168.0.151 non-persistent-redis 1/1
Running 1 1h 172.16.0.20 192.168.0.151 task-pv-pod 1/1 Running 0 1h 172.16.0.19
192.168.0.151[root@cce-demo1522483688765-00274 cka]# kubectl exec -it busybox1
-- nslookup 172-16-0-22.default.pod.cluster.local Server: 10.247.3.10 Address
1: 10.247.3.10 kube-dns.kube-system.svc.cluster.local Name:
172-16-0-22.default.pod.cluster.local Address 1: 172.16.0.22[
root@cce-demo1522483688765-00274 cka]# root@lhys:~# kubectl exec -it busybox1
-- nslookup default-subdomain Server: 10.247.3.10 Address 1: 10.247.3.10
coredns.kube-system.svc.cluster.local Name: default-subdomain Address 1:
172.16.0.9 busybox-2.default-subdomain.default.svc.cluster.local Address 2:
172.16.0.8 busybox-1.default-subdomain.default.svc.cluster.local root@lhys:~#
kubectl exec -it busybox1 -- nslookup busybox-2.default-subdomain Server:
10.247.3.10 Address 1: 10.247.3.10 coredns.kube-system.svc.cluster.local Name:
busybox-2.default-subdomain Address 1: 172.16.0.9
busybox-2.default-subdomain.default.svc.cluster.local
<>使用clusterIP svc配置pod的hostname、subdomain

* 关键点在于为pod配置hostname和subdomain,subdomain为svc
* 并且保证svc的selector能够找到pod的label；比如下边例子中svc的selector
key:value用run:hello-nginx,pods的label key:value用run:hello-nginx,因此svc能够找到pods
SVC:
apiVersion: v1 kind: Service metadata: creationTimestamp:
"2019-07-02T05:15:07Z" labels: app: ng-pods name: ng-pods namespace: default
spec: clusterIP: 10.101.41.59 ports: - name: 80-8899 port: 80 protocol: TCP
targetPort: 8899 selector: run: hello-nginx #重要，用来关联pods type: ClusterIP
POD:
apiVersion: v1 kind: Pod metadata: labels: run: hello-nginx #label
和svc的selector关联 name: hello-nginx spec: containers: - image: nginx name: hello-
nginxrestartPolicy: Always hostname: hello-nginx #hostname subdomain: ng-pods
#配置的svc
测试:
root@node1:~# kubectl get svc NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1<none> 443/TCP 2d21h ng-pods ClusterIP
10.101.41.59<none> 80/TCP 9m37s root@node1:~# kubectl get pods NAME READY
STATUS RESTARTS AGE busybox 1/1 Running 69 2d21h hello-nginx 1/1 Running 0
6m16s root@node1:~# kubectl exec -it busybox -- nslookup ng-pods Server:
10.96.0.10 Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local Name:
ng-pods Address 1: 10.101.41.59 ng-pods.default.svc.cluster.local root@node1:~#
kubectl exec -it busybox -- nslookup hello-nginx.ng-pods Server: 10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local Name:
hello-nginx.ng-pods Address 1: 10.244.0.14
10-244-0-14.my-nginx.default.svc.cluster.local root@node1:~#

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