tags: addons, dns, coredns

09-1.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：

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

$ kubectl get services --all-namespaces |grep my-nginx
default       my-nginx     ClusterIP   10.254.242.255   <none>        80/TCP          9s

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 10.254.242.255

$ 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 (10.254.242.255): 48 data bytes
56 bytes from 10.254.242.255: icmp_seq=0 ttl=64 time=0.115 ms
^C--- my-nginx.default.svc.cluster.local ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.115/0.115/0.115/0.000 ms


root@nginx:/# ping my-nginx
PING my-nginx.default.svc.cluster.local (10.254.63.136): 48 data bytes
^C--- my-nginx.default.svc.cluster.local ping statistics ---
4 packets transmitted, 0 packets received, 100% packet loss

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=0.097 ms
56 bytes from 10.254.0.1: icmp_seq=1 ttl=64 time=0.123 ms
^C--- kubernetes.default.svc.cluster.local ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.097/0.110/0.123/0.000 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=0.129 ms
^C--- coredns.kube-system.svc.cluster.local ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.129/0.129/0.129/0.000 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