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09-1.部署CoreDNS插件.md

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tags: addons, dns, coredns

09-1.部署 coredns 插件

修改配置文件 coredns.yaml

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：

[admin@k8s-admin ~]$ ls kubernetes/
addons  kubernetes-src.tar.gz  LICENSES  server
[admin@k8s-admin ~]$ mkdir kubernetes/kubernetes-src
[admin@k8s-admin ~]$ tar -zxf kubernetes/kubernetes-src.tar.gz -C kubernetes/kubernetes-src
[admin@k8s-admin ~]$ ls kubernetes/kubernetes-src/cluster/addons/dns/coredns
coredns.yaml.base  coredns.yaml.in  coredns.yaml.sed  Makefile  transforms2salt.sed  transforms2sed.sed
[admin@k8s-admin ~]$ cp -R kubernetes/kubernetes-src/cluster/addons/dns/coredns yaml/

修改 coredns 配置文件：

[admin@k8s-admin ~]$ source environment.sh
[admin@k8s-admin ~]$ cp yaml/coredns/coredns.yaml.base yaml/coredns/coredns.yaml
[admin@k8s-admin ~]$ sed -i "{
  s/__PILLAR__DNS__SERVER__/$DNS_SERVER_IP/g
  s/__PILLAR__DNS__DOMAIN__/$DNS_DOMAIN/g
  s/image: k8s.gcr.io/image: coredns/g
}" yaml/coredns/coredns.yaml
  • 注意，这里使用的是双引号，这样才能替换 $DNS_SERVER_IP 和 $DNS_DOMAIN 两个变量。

创建 coredns

[admin@k8s-admin ~]$ kubectl create -f yaml/coredns/coredns.yaml
serviceaccount/coredns created
clusterrole.rbac.authorization.k8s.io/system:coredns created
clusterrolebinding.rbac.authorization.k8s.io/system:coredns created
configmap/coredns created
deployment.extensions/coredns created
service/kube-dns created

检查 coredns 功能

[admin@k8s-admin ~]$ kubectl get all -n kube-system
NAME                          READY   STATUS    RESTARTS   AGE
pod/coredns-dc8bbbcf9-w62r9   1/1     Running   0          58s

NAME               TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)         AGE
service/kube-dns   ClusterIP   10.0.0.2     <none>        53/UDP,53/TCP   16m

NAME                      READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/coredns   1/1     1            1           38m

NAME                                DESIRED   CURRENT   READY   AGE
replicaset.apps/coredns-dc8bbbcf9   1         1         1       58s
replicaset.apps/coredns-fff89c9b9   0         0         0       38m

[admin@k8s-admin ~]$ kubectl get clusterrole system:coredns
NAME             AGE
system:coredns   30m
[admin@k8s-admin ~]$ kubectl get clusterrolebinding  system:coredns
NAME             AGE
system:coredns   30m

新建一个 Deployment

[admin@k8s-admin ~]$ cat > yaml/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:latest
        ports:
        - containerPort: 80
EOF
[admin@k8s-admin ~]$ kubectl create -f yaml/my-nginx.yaml
deployment.extensions/my-nginx created

Export 该 Deployment, 生成 my-nginx 服务：

[admin@k8s-admin ~]$ kubectl expose deployment my-nginx
service/my-nginx exposed

[admin@k8s-admin ~]$ kubectl get service
NAME         TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.0.0.1      <none>        443/TCP   44h
my-nginx     ClusterIP   10.0.11.108   <none>        80/TCP    20s

创建另一个 Pod，查看 /etc/resolv.conf 是否包含 kubelet 组件的 --config 参数指定的配置文件（这里是 /etc/kubernetes/kubelet.config.yaml）中的 clusterDNS 和 clusterDomain（或者 --cluster-dns 和 --cluster-domain 参数）：

[admin@k8s-admin ~]$ kubectl run -it dnsutils --image=tutum/dnsutils:latest --generator=run-pod/v1
If you don't see a command prompt, try pressing enter.
root@dnsutils:/#
root@dnsutils:/# cat /etc/resolv.conf
nameserver 10.0.0.2
search default.svc.cluster.local svc.cluster.local cluster.local
options ndots:5
  • 如果这里的 nameserver 不正确，检查 kubelet 组件的 config 参数指定的配置文件（这里是 /etc/kubernetes/kubelet.config.yaml）中的 clusterDNS 是否设置正确。

检查是否能够将服务 my-nginx 解析到上面显示的 Cluster IP 10.0.11.108：

[admin@k8s-admin ~]$ kubectl exec -it dnsutils -- bash
root@dnsutils:/# nslookup kubernetes
Server:		10.0.0.2
Address:	10.0.0.2#53

Name:	kubernetes.default.svc.cluster.local
Address: 10.0.0.1

root@dnsutils:/# nslookup my-nginx
Server:		10.0.0.2
Address:	10.0.0.2#53

Name:	my-nginx.default.svc.cluster.local
Address: 10.0.11.108

root@dnsutils:/# nslookup www.baidu.com
Server:		10.0.0.2
Address:	10.0.0.2#53

Non-authoritative answer:
www.baidu.com	canonical name = www.a.shifen.com.
Name:	www.a.shifen.com
Address: 180.97.33.107
Name:	www.a.shifen.com
Address: 180.97.33.108

root@dnsutils:/# nslookup www.baidu.com.
Server:		10.0.0.2
Address:	10.0.0.2#53

Non-authoritative answer:
www.baidu.com	canonical name = www.a.shifen.com.
Name:	www.a.shifen.com
Address: 180.97.33.108
Name:	www.a.shifen.com
Address: 180.97.33.107

参考

  1. https://community.infoblox.com/t5/Community-Blog/CoreDNS-for-Kubernetes-Service-Discovery/ba-p/8187
  2. https://coredns.io/2017/03/01/coredns-for-kubernetes-service-discovery-take-2/
  3. https://www.cnblogs.com/boshen-hzb/p/7511432.html
  4. https://github.com/kubernetes/kubernetes/tree/master/cluster/addons/dns