内容转载自：https://github.com/opsnull/follow-me-install-kubernetes-cluster/blob/master/09-1.dns%E6%8F%92%E4%BB%B6.md

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tags: addons, dns, coredns

09.部署 coredns 插件

修改配置文件

将下载的 kubernetes-server-linux-amd64.tar.gz 解压后，再解压其中的 kubernetes-src.tar.gz 文件。

coredns 对应的目录是：cluster/addons/dns。

$ pwd
/opt/k8s/kubernetes/cluster/addons/dns

$ cp coredns.yaml.base coredns.yaml
$ diff coredns.yaml.base coredns.yaml
61c61
<         kubernetes __PILLAR__DNS__DOMAIN__ in-addr.arpa ip6.arpa {
---
>         kubernetes cluster.local. in-addr.arpa ip6.arpa {
153c153
<   clusterIP: __PILLAR__DNS__SERVER__
---
>   clusterIP: 10.254.0.2

创建 coredns

$ kubectl create -f coredns.yaml

检查 coredns 功能

$ kubectl get all -n kube-system
NAME                           READY     STATUS    RESTARTS   AGE
pod/coredns-77c989547b-6l6jr   1/1       Running   0          3m
pod/coredns-77c989547b-d9lts   1/1       Running   0          3m

NAME              TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)         AGE
service/coredns   ClusterIP   10.254.0.2   <none>        53/UDP,53/TCP   3m

NAME                      DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/coredns   2         2         2            2           3m

NAME                                 DESIRED   CURRENT   READY     AGE
replicaset.apps/coredns-77c989547b   2         2         2         3m

新建一个 Deployment

$ cat > my-nginx.yaml <<EOF
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: my-nginx
spec:
  replicas: 2
  template:
    metadata:
      labels:
        run: my-nginx
    spec:
      containers:
      - name: my-nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80
EOF
$ kubectl create -f my-nginx.yaml

Export 该 Deployment, 生成 my-nginx 服务：

[root@k8s-master-0001 ~]# kubectl expose deploy my-nginx
service "my-nginx" exposed
[root@k8s-master-0001 ~]# kubectl get services --all-namespaces |grep my-nginx
default       my-nginx     ClusterIP   10.254.94.101    <none>        80/TCP          6s

创建另一个 Pod，查看 /etc/resolv.conf 是否包含 kubelet 配置的 --cluster-dns 和 --cluster-domain，是否能够将服务 my-nginx 解析到上面显示的 Cluster IP 10.254.94.101

$ cat > pod-nginx.yaml <<EOF
apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
  - name: nginx
    image: nginx:1.7.9
    ports:
    - containerPort: 80
EOF

$ kubectl create -f pod-nginx.yaml
$ kubectl exec  nginx -i -t -- /bin/bash
root@nginx:/# cat /etc/resolv.conf
nameserver 10.254.0.2
search default.svc.cluster.local. svc.cluster.local. cluster.local. 4pd.io
options ndots:5

root@nginx:/#  ping my-nginx
PING my-nginx.default.svc.cluster.local (10.254.94.101): 48 data bytes
56 bytes from 10.254.94.101: icmp_seq=0 ttl=64 time=0.040 ms
56 bytes from 10.254.94.101: icmp_seq=1 ttl=64 time=0.076 ms
^C--- my-nginx.default.svc.cluster.local ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.040/0.058/0.076/0.000 ms
root@nginx:/# ping my-nginx
PING my-nginx.default.svc.cluster.local (10.254.94.101): 48 data bytes
56 bytes from 10.254.94.101: icmp_seq=0 ttl=64 time=0.034 ms
56 bytes from 10.254.94.101: icmp_seq=1 ttl=64 time=0.088 ms
^C--- my-nginx.default.svc.cluster.local ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.034/0.061/0.088/0.027 ms
root@nginx:/#  ping kubernetes
PING kubernetes.default.svc.cluster.local (10.254.0.1): 48 data bytes
56 bytes from 10.254.0.1: icmp_seq=0 ttl=64 time=0.036 ms
56 bytes from 10.254.0.1: icmp_seq=1 ttl=64 time=0.064 ms
^C--- kubernetes.default.svc.cluster.local ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.036/0.050/0.064/0.000 ms
root@nginx:/# ping coredns.kube-system.svc.cluster.local
PING coredns.kube-system.svc.cluster.local (10.254.0.2): 48 data bytes
56 bytes from 10.254.0.2: icmp_seq=0 ttl=64 time=0.036 ms
56 bytes from 10.254.0.2: icmp_seq=1 ttl=64 time=0.058 ms
^C--- coredns.kube-system.svc.cluster.local ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.036/0.047/0.058/0.000 ms

参考

https://community.infoblox.com/t5/Community-Blog/CoreDNS-for-Kubernetes-Service-Discovery/ba-p/8187

https://coredns.io/2017/03/01/coredns-for-kubernetes-service-discovery-take-2/ https://www.cnblogs.com/boshen-hzb/p/7511432.html 

https://github.com/kubernetes/kubernetes/tree/master/cluster/addons/dns

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