DNS (domain name system),提供域名解析服务，解决了难于记忆的IP地址问题，以更人性可读可记忆可标识的方式映射对应IP地址。

Cluster DNS扩展插件用于支持k8s集群系统中各服务之间发现与调用。

　　

组件：

　　•SkyDNS 提供DNS解析服务

　　•Etcd 存储DNS信息

　　•Kube2sky 监听kubernetes，当有Service创建时，生成相应的记录到SkyDNS。

 

本文章的实验环境与《》介绍中一致。master(1) + node(4)

1.修改所有node的配置文件：/etc/kubernetes/kubelet

node1,node2,node3.node4:

[root@node1 ~]# tail -n 1 /etc/kubernetes/kubelet

KUBELET_ARGS="--cluster-dns=10.254.254.254 --cluster-domain=cluster.local"

2.所有node(node1,node2,node3,node4)重新启动kubelet服务

[root@node1 ~]# systemctl restart kubelet.service

3.根据namespace分为不同的名称空间，将系统服务统一放到一个单独的空间：kube-system，由于默认空间只有default，我们首先要创建kube-system空间。

[root@master skydns]# cat kube-system.yml

apiVersion: v1kind: Namespacemetadata:  name: kube-system

4.在master服务器上编辑ReplicationController文件skydns-rc.yml

[root@master skydns]# cat skydns-rc.yml

apiVersion: v1kind: ReplicationControllermetadata:  name: kube-dns-v11  namespace: kube-system  labels:    k8s-app: kube-dns    version: v11    kubernetes.io/cluster-service: "true"spec:  replicas: 1  selector:    k8s-app: kube-dns    version: v11  template:    metadata:      labels:        k8s-app: kube-dns        version: v11        kubernetes.io/cluster-service: "true"    spec:      containers:      - name: etcd        image: docker.gaoxiaobang.com/kubernetes/etcd-amd64:2.2.1          resources:          limits:            cpu: 100m            memory: 500Mi          requests:            cpu: 100m            memory: 50Mi        command:        - /usr/local/bin/etcd        - -data-dir        - /var/etcd/data        - -listen-client-urls        - http://127.0.0.1:2379,http://127.0.0.1:4001        - -advertise-client-urls        - http://127.0.0.1:2379,http://127.0.0.1:4001        - -initial-cluster-token        - skydns-etcd        #volumeMounts:        #- name: etcd-storage        #  mountPath: /var/etcd/data      - name: kube2sky        image: docker.gaoxiaobang.com/kubernetes/kube2sky:1.14        args:        # command = "/kube2sky"        - --domain=cluster.local        - --kube-master-url=http://192.168.30.20:8080        resources:          limits:            cpu: 100m            memory: 200Mi          requests:            cpu: 100m            memory: 50Mi      - name: skydns        image: docker.gaoxiaobang.com/kubernetes/skydns:2015-10-13-8c72f8c        resources:          limits:            cpu: 100m            memory: 200Mi          requests:            cpu: 100m            memory: 50Mi        args:        - -machines=http://127.0.0.1:4001        - -addr=0.0.0.0:53        - -ns-rotate=false        - -domain=cluster.local.        ports:        - containerPort: 53          name: dns          protocol: UDP        - containerPort: 53          name: dns-tcp          protocol: TCP        livenessProbe:          httpGet:            path: /healthz            port: 8080            scheme: HTTP          initialDelaySeconds: 60          timeoutSeconds: 5          successThreshold: 1          failureThreshold: 5        readinessProbe:          httpGet:            path: /readiness            port: 8080            scheme: HTTP          initialDelaySeconds: 30          timeoutSeconds: 5      - name: healthz        image: docker.gaoxiaobang.com/kubernetes/exechealthz:1.0        resources:          limits:            cpu: 10m            memory: 20Mi          requests:            cpu: 10m            memory: 20Mi        args:        - -cmd=nslookup kubernetes.default.svc.cluster.local localhost >/dev/null        - -port=8080        ports:        - containerPort: 8080          protocol: TCP      volumes:      - name: etcd-storage        emptyDir: {}      dnsPolicy: Default

5.在master上创建skydns服务文件skydns-svc.yml

[root@master skydns]# cat skydns-svc.yml

apiVersion: v1kind: Servicemetadata:  name: kube-dns  namespace: kube-system  labels:    k8s-app: kube-dns    kubernetes.io/cluster-service: "true"    kubernetes.io/name: "KubeDNS"spec:  selector:    k8s-app: kube-dns  clusterIP:  10.254.254.254  ports:  - name: dns    port: 53    protocol: UDP  - name: dns-tcp    port: 53    protocol: TCP

6.在集群中创建cluster-dns解析应用

•创建Namespace

[root@master skydns]# kubectl create -f kube-system.yml

•创建ReplicationController

[root@master skydns]# kubectl create -f skydns-rc.yml

•创建Service

[root@master skydns]# kubectl create -f skydns-svc.yml

7.查看skydns-rc.yml文件中定义pod的启动状态，如下则启动成功。

[root@master skydns]# kubectl get pod --namespace=kube-systemNAME                         READY     STATUS    RESTARTS   AGEkube-dns-v11-ey14j           4/4       Running   8          1d

8.查看skydns-svc.yml文件中定义的Service的信息。

[root@master skydns]# kubectl get svc -l k8s-app=kube-dns --namespace=kube-systemNAME       CLUSTER-IP       EXTERNAL-IP   PORT(S)         AGEkube-dns   10.254.254.254   
     
              53/UDP,53/TCP   1d
     

9.测试DNS的效果。

•部署一个busybox的Pod

[root@master test]# cat busybox.yml

apiVersion: v1kind: Podmetadata:  name: busybox  namespace: defaultspec:  containers:  - image: busybox    command:      - sleep      - "3600"    imagePullPolicy: IfNotPresent    name: busybox  restartPolicy: Always

•验证kubernetes服务的地址解析，出现如下所示则证明DNS解析正常。

[root@master test]# kubectl exec busybox nslookup kubernetesServer:    10.254.254.254Address 1: 10.254.254.254Name:      kubernetesAddress 1: 10.254.0.1

*提示：kubernetes服务是kubernetes集群安装之后默认的一个服务。