k8s入门系列之扩展组件(一)DNS安装篇

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《k8s入门系列之集群安装篇》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:

[[email protected] ~]# 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

[[email protected] ~]# 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。

[[email protected] skydns]# cat kube-system.yml

apiVersion: v1
kind: Namespace
metadata:
  name: kub-system

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

[[email protected] skydns]# cat skydns-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://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
[[email protected] skydns]# cat skydns-svc.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

6.在集群中创建cluster-dns解析应用

?创建Namespace

[[email protected] skydns]# kubectl create -f kube-system.yml

?创建ReplicationController

[[email protected] skydns]# kubectl create -f skydns-rc.yml

?创建Service

[[email protected] 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。

[[email protected] skydns]# kubectl get pod --namespace=kube-system
NAME                         READY     STATUS    RESTARTS   AGE
kube-dns-v11-ey14j           4/4       Running   8          1d

8.查看skydns-svc.yml文件中定义的Service的信息。

[[email protected] skydns]# kubectl get svc -l k8s-app=kube-dns --namespace=kube-system
NAME       CLUSTER-IP       EXTERNAL-IP   PORT(S)         AGE
kube-dns   10.254.254.254   <none>        53/UDP,53/TCP   1d

9.测试DNS的效果。
?部署一个busybox的Pod
[[email protected] test]# cat busybox.yml

apiVersion: v1
kind: Pod
metadata:
  name: busybox
  namespace: default
spec:
  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。

[[email protected] test]# kubectl exec busybox nslookup kubernetes
Server:    10.254.254.254
Address 1: 10.254.254.254

Name:      kubernetes
Address 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。