1，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
/home/k8s/k8s/kubernetes/cluster/addons/dns

$ cp coredns.yaml.base coredns.yaml

#修改第61行以及第153行的内容。
$vim coredns.yaml

#修改后内容与原内容对比如下：
$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

2，创建 coredns

$ kubectl create -f coredns.yaml

3， 检查 coredns 功能

$ kubectl get all -n kube-system
NAME                                        READY     STATUS    RESTARTS   AGE
pod/coredns-77c989547b-j77lp                1/1       Running   0          15h
pod/coredns-77c989547b-t6mxc                1/1       Running   0          15h

NAME                           TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)         AGE
service/coredns                ClusterIP   10.254.0.2             53/UDP,53/TCP   15h


NAME                                   DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/coredns                2         2         2            2           15h

NAME                                              DESIRED   CURRENT   READY     AGE
replicaset.apps/coredns-77c989547b                2         2         2         15h

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：

$ kubectl expose deploy my-nginx
service "my-nginx" exposed

$kubectl get services --all-namespaces |grep my-nginx
default       my-nginx               ClusterIP   10.254.22.37             80/TCP           15h

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 10.254.22.37。

$ cat > pod-nginx.yaml <

$ kubectl create -f pod-nginx.yaml

$ kubectl exec  nginx -i -t -- /bin/bash

$kubectl exec -it nginx bash

root@nginx:/# cat /etc/resolv.conf 
nameserver 10.254.0.2
search default.svc.cluster.local. svc.cluster.local. cluster.local.
options ndots:5

root@nginx:/# ping my-nginx
PING my-nginx.default.svc.cluster.local (10.254.22.37): 48 data bytes
56 bytes from 10.254.22.37: icmp_seq=0 ttl=64 time=0.118 ms
56 bytes from 10.254.22.37: icmp_seq=1 ttl=64 time=0.085 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 = 0.085/0.102/0.118/0.000 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=0.111 ms
56 bytes from 10.254.0.1: icmp_seq=1 ttl=64 time=0.098 ms
^C--- kubernetes.default.svc.cluster.local ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.098/0.105/0.111/0.000 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=0.120 ms
56 bytes from 10.254.0.2: icmp_seq=1 ttl=64 time=0.083 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 = 0.083/0.102/0.120/0.000 ms