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。

1.修改所有node的配置文件：/etc/kubernetes/kubelet  kubernetes-node1，kubernetes-node2，kubernetes-node3:

[root@kubernetes-node2 ~]# tail -n 1 /etc/kubernetes/kubelet

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

2.所有node节点都重新启动服务

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@kubernetes-master pods]# cat kube-system.yml

apiVersion: v1

kind: Namespace

metadata:

name: kube-system

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

1 apiVersion: v12 kind: ReplicationController3 metadata:4 name: kube-dns-v115 namespace: kube-system6 labels:7 k8s-app: kube-dns8 version: v119 kubernetes.io/cluster-service: "true"10 spec:11 replicas: 112 selector:13 k8s-app: kube-dns14 version: v1115 template:16 metadata:17 labels:18 k8s-app: kube-dns19 version: v1120 kubernetes.io/cluster-service: "true"21 spec:22 containers:23 - name: etcd24 image: docker.gaoxiaobang.com/kubernetes/etcd-amd64:2.2.125 resources:26 limits:27 cpu: 100m28 memory: 500Mi29 requests:30 cpu: 100m31 memory: 50Mi32 command:33 - /usr/local/bin/etcd34 - -data-dir35 - /var/etcd/data36 - -listen-client-urls37 - http://127.0.0.1:2379,http://127.0.0.1:400138 - -advertise-client-urls39 - http://127.0.0.1:2379,http://127.0.0.1:400140 - -initial-cluster-token41 - skydns-etcd42 #volumeMounts:43 #- name: etcd-storage44 # mountPath: /var/etcd/data45 - name: kube2sky46 image: docker.gaoxiaobang.com/kubernetes/kube2sky:1.1447 args:48 # command = "/kube2sky"49 - --domain=cluster.local50 - --kube-master-url=http://10.64.8.68:808051 resources:52 limits:53 cpu: 100m54 memory: 200Mi55 requests:56 cpu: 100m57 memory: 50Mi58 - name: skydns59 image: docker.gaoxiaobang.com/kubernetes/skydns:2015-10-13-8c72f8c60 resources:61 limits:62 cpu: 100m63 memory: 200Mi64 requests:65 cpu: 100m66 memory: 50Mi67 args:68 - -machines=http://127.0.0.1:400169 - -addr=0.0.0.0:5370 - -ns-rotate=false71 - -domain=cluster.local.72 ports:73 - containerPort: 5374 name: dns75 protocol: UDP76 - containerPort: 5377 name: dns-tcp78 protocol: TCP79 livenessProbe:80 httpGet:81 path: /healthz82 port: 808083 scheme: HTTP84 initialDelaySeconds: 6085 timeoutSeconds: 586 successThreshold: 187 failureThreshold: 588 readinessProbe:89 httpGet:90 path: /readiness91 port: 808092 scheme: HTTP93 initialDelaySeconds: 3094 timeoutSeconds: 595 - name: healthz96 image: docker.gaoxiaobang.com/kubernetes/exechealthz:1.097 resources:98 limits:99 cpu: 10m100 memory: 20Mi101 requests:102 cpu: 10m103 memory: 20Mi104 args:105 - -cmd=nslookup kubernetes.default.svc.cluster.local localhost >/dev/null106 - -port=8080107 ports:108 - containerPort: 8080109 protocol: TCP110 volumes:111 - name: etcd-storage112 emptyDir: {}113 dnsPolicy: Default

dns-rc.yml

注意dns-rc.yml：修改文件中的master ip

dns service服务yml

1 apiVersion: v12 kind: Service3 metadata:4 name: kube-dns5 namespace: kube-system6 labels:7 k8s-app: kube-dns8 kubernetes.io/cluster-service: "true"9 kubernetes.io/name: "KubeDNS"10 spec:11 selector:12 k8s-app: kube-dns13 clusterIP: 10.254.254.25414 ports:15 - name: dns16 port: 5317 protocol: UDP18 - name: dns-tcp19 port: 5320 protocol: TCP

dns-svc.yml

创建namespace(有就不用在创建了)

kubectl create -f kube-system.yml

创建ReplicationController

[root@kubernetes-master pods]# kubectl create -f dns-rc.yml

创建Service

[root@kubernetes-master pods]# kubectl create -f dns-svc.yml

查看dns-rc.yml文件中定义pod的启动状态，如下则启动成功。

[root@kubernetes-master pods]#  kubectl get pod --namespace=kube-system

查看dns-svc.yml文件中定义的Service的信息。

[root@kubernetes-master pods]# kubectl get svc -l k8s-app=kube-dns --namespace=kube-system

测试DNS的效果。

部署一个busybox的Pod

1 apiVersion: v12 kind: Pod3 metadata:4 name: busybox5 namespace: default6 spec:7 containers:8 - image: busybox9 command:10 - sleep11 - "3600"12 imagePullPolicy: IfNotPresent13 name: busybox14 restartPolicy: Always

busybox.yml

验证kubernetes服务的地址解析，出现如下所示则证明DNS解析正常。