部署 coredns 插件

意：如果没有特殊指明，本文档的所有操作均在 K8s-master1 节点上执行。

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。

cd /opt/k8s/work/kubernetes/cluster/addons/dns/coredns
cp coredns.yaml.base coredns.yaml
source /opt/k8s/bin/environment.sh
sed -i -e "s/__PILLAR__DNS__DOMAIN__/${CLUSTER_DNS_DOMAIN}/" -e "s/__PILLAR__DNS__SERVER__/${CLUSTER_DNS_SVC_IP}/" coredns.yaml

创建 coredns

kubectl create -f coredns.yaml

检查 coredns 功能

[root@k8s-master1 coredns]# kubectl get all -n kube-system
NAME                           READY   STATUS              RESTARTS   AGE
pod/coredns-5b969f4c88-wfn6g   0/1     ContainerCreating   0          13s

NAME               TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)                  AGE
service/kube-dns   ClusterIP   10.254.0.2   <none>        53/UDP,53/TCP,9153/TCP   13s

NAME                      READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/coredns   0/1     1            0           13s

NAME                                 DESIRED   CURRENT   READY   AGE
replicaset.apps/coredns-5b969f4c88   1         1         0       13s

如果出现coredns镜像拉取失败,在每个工作节点上执行

images=(
    coredns:1.3.1
)

for imageName in ${images[@]} ; do
    docker pull registry.cn-hangzhou.aliyuncs.com/google_containers/$imageName
    docker tag registry.cn-hangzhou.aliyuncs.com/google_containers/$imageName k8s.gcr.io/$imageName
done

新建一个 Deployment

cd /opt/k8s/work
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-master1 work]# kubectl expose deploy my-nginx
service/my-nginx exposed
[root@k8s-master1 work]# kubectl get services --all-namespaces |grep my-nginx
default       my-nginx     ClusterIP   10.254.110.68   <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 10.254.242.255

cd /opt/k8s/work
cat > dnsutils-ds.yml <<EOF
apiVersion: v1
kind: Service
metadata:
  name: dnsutils-ds
  labels:
    app: dnsutils-ds
spec:
  type: NodePort
  selector:
    app: dnsutils-ds
  ports:
  - name: http
    port: 80
    targetPort: 80
---
apiVersion: extensions/v1beta1
kind: DaemonSet
metadata:
  name: dnsutils-ds
  labels:
    addonmanager.kubernetes.io/mode: Reconcile
spec:
  template:
    metadata:
      labels:
        app: dnsutils-ds
    spec:
      containers:
      - name: my-dnsutils
        image: tutum/dnsutils:latest
        command:
          - sleep
          - "3600"
        ports:
        - containerPort: 80
EOF
kubectl create -f dnsutils-ds.yml

[root@k8s-master1 coredns]# kubectl exec dnsutils-ds-9t5r5 nslookup kubernetes
Server:        10.254.0.2
Address:    10.254.0.2#53

Name:    kubernetes.default.svc.cluster.local
Address: 10.254.0.1