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10.核心组件安装之 coreDNS

下载相关文件

$ wget https://github.com/coredns/deployment/blob/master/kubernetes/deploy.sh
$ wget https://github.com/coredns/deployment/blob/master/kubernetes/coredns.yaml.sed

运行相关pod

$ ./deploy.sh -r 10.254.0.0/16 -i 10.254.0.2 -d cluster.local -s | kubectl apply -f -

提示：关于脚本的内容可能会因为你使用的版本不同而参数不同，所以尽量在做的时候撸一眼脚本的内容。

$ kubectl get pod -n kube-system|grep coredns
coredns-7bb49b45c8-89d2v                   1/1     Running   0          41s
coredns-7bb49b45c8-gr8dj                   1/1     Running   0          41s

部署测试nginx pod进行测试

$ 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
$ kubectl expose deploy my-nginx

查看运行的nginx服务

$ kubectl get services --all-namespaces |grep my-nginx
default       my-nginx     ClusterIP   10.254.79.234   <none>        80/TCP          7s

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 10.254.79.234

$ 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

查看运行的pod

$ kubectl get pod --all-namespaces |grep nginx
default       my-nginx-75bbc97767-hsqbt                  1/1     Running   0          49s
default       my-nginx-75bbc97767-sxtfj                  1/1     Running   0          49s
default       nginx                                      1/1     Running   0          18s

测试DNS是否正常

$ 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.
options ndots:5

root@nginx:/# ping my-nginx
PING my-nginx.default.svc.cluster.local (10.254.155.155): 48 data bytes
56 bytes from 10.254.155.155: icmp_seq=0 ttl=64 time=0.523 ms
56 bytes from 10.254.155.155: icmp_seq=1 ttl=64 time=0.083 ms
^C--- my-nginx.default.svc.cluster.local ping statistics ---

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=0.055 ms
56 bytes from 10.254.0.1: icmp_seq=1 ttl=64 time=0.111 ms
56 bytes from 10.254.0.1: icmp_seq=2 ttl=64 time=0.103 ms
^C--- kubernetes.default.svc.cluster.local ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.055/0.090/0.111/0.025 ms

root@nginx:/# ping kube-dns.kube-system.svc.cluster.local
PING kube-dns.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=0.141 ms
56 bytes from 10.254.0.2: icmp_seq=1 ttl=64 time=0.110 ms
56 bytes from 10.254.0.2: icmp_seq=2 ttl=64 time=0.110 ms
^C--- kube-dns.kube-system.svc.cluster.local ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.110/0.120/0.141/0.000 ms

如果跟上面显示一样，就没有问题了。

删除coredns

kubectl delete --namespace=kube-system deployment kube-dns

遇到的问题：
kubernetes 使用基于 alpine 镜像无法正常解析外网DNS