配置k8s dns

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

 apiVersion: v1
 kind: ReplicationController
 metadata:
   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://10.64.8.68:8080
         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

dns-rc.yml

注意dns-rc.yml：修改文件中的master ip

dns service服务yml

 apiVersion: v1
 kind: Service
 metadata:
   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

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

 apiVersion: v1
 kind: Pod
 metadata:
   name: busybox
   namespace: default
 spec:
   containers:
   - image: busybox
     command:
       - sleep
       - "3600"
     imagePullPolicy: IfNotPresent
     name: busybox
   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。