k8s之DNS服务器搭建

女爷i 2022-10-07 03:59 310阅读 0赞

一、导读

在使用k8s部署springboot+redis简单应用这篇文章中，spring boot连接redis是直接使用的IP连接，那么可不可以直接使用服务名称进行连接呢？答案是可以的，这就是k8s集群范围内的DNS服务来完成服务名到ClusterIP的解析，接下来就一起看一下如何搭建DNS服务器。

二、搭建DNS服务器

（1）简介

k8s提供的DNS服务是skydns，由四个组件组成

*  etcd：DNS信息存储
 *  kube2sky：监控k8s中Service资源的变化，根据Service的名称的IP地址信息生成DNS记录，并将其保存到etcd中
 *  skyDNS：从etcd中读取DNS信息，并提供DNS查询服务
 *  healthz：提供对skydns服务的健康检查功能

![b70b8bd4faa650711adffe467e099f80.png][]

（2）skydns配置文件说明

skydns服务有一个RC和一个Service组成，分别由配置文件skydns-rc.yaml和skydns-svc.yaml定义。

skydns-rc.yaml包含了四个容器的定义：

apiVersion: v1
    kind: ReplicationController
    metadata:
      name: kube-dns-v8
      namespace: kube-system
      labels:
        k8s-app: kube-dns
        version: v8
        kubernetes.io/cluster-service: "true"
    spec:
      replicas: 1
      selector:
        k8s-app: kube-dns
        version: v8
      template:
        metadata:
          labels:
            k8s-app: kube-dns
            version: v8
            kubernetes.io/cluster-service: "true"
        spec:
          containers:
          - name: etcd
            image: empiregeneral/etcd-amd64:latest
            resources:
              limits:
                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: syncgooglecontainers/kube2sky-amd64:1.15
            resources:
              limits:
                cpu: 100m
                memory: 50Mi
            args:
            - --domain=cluster.local
            - --kube_master_url=http://192.168.197.100:8080
          - name: skydns
            image: yaronr/skydns:latest
            resources:
              limits:
                cpu: 100m
                memory: 50Mi
            args:
            - -machines=http://localhost:4001
            - -addr=0.0.0.0:53
            - -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: 30
              timeoutSeconds: 5
          - name: healthz
            image: syncgooglecontainers/exechealthz:1.1
            resources:
              limits:
                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  # Don't use cluster DNS.

上述需要注意的是，需要将

--kube_master_url=http://192.168.197.100:8080

改成集群中master的IP，镜像如果下载失败，可从docker hub里面找，我就是从docker hub里面找到相应的镜像。

skydns-svc.yaml

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: 10.96.0.10
      ports:
      - name: dns
        port: 53
        protocol: UDP
      - name: dns-tcp
        port: 53
        protocol: TCP

需要指定一个clusterIP，不能靠k8s自动分配，每个Node的kubelet都是用这个IP地址，另外，这个IP需要在kube-apiserver启动参数--service-cluster-ip-range指定的IP范围内

kube-apiserver的配置文件在/etc/kubernetes/manifests目录下：

![f11eccc086b4a8baf7d8a1d249170133.png][]

（3）修改每台Node上的kubelet参数

添加以下两个参数：

--cluster_dns=169.169.0.100: 为dns服务的clusterIP地址
    --cluster_domain=cluster.local: 为dns服务中设置的域名

比如我这边的是这样：

vim /usr/lib/systemd/system/kubelet.service.d/10-kubeadm.conf
    #添加如下一行
    Environment="KUBELET_DNS_ARGS=--cluster-dns=10.96.0.10 --cluster-domain=cluster.local"

然后重启kubelet，使用ps -ef | grep kubelet查看是否生效

重启kubelet

systemctl stop kubelet
    systemctl daemon-reload
    systemctl start kubelet

![6d129b4ba25a2de328d9fbbce81793ca.png][]

修改完参数之后，启动dns

kubectl create -f skydns-rc.yaml
    kubectl create -f skydns-svc.yaml

（4）验证

启动一个busybox容器。

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

启动之后进入容器内部：

nsloogup 服务名

![7dcdf87cfa6c55728426d645738ccf35.png][]

可知解析后的ip是10.102.184.126。

然后查找对应的redis 的Service的ip，可以看到，两个IP是对的上的。

![f39cd734d4dda6a58ea508f91dab737a.png][]

又例如之前的springboot连接redis：

在构建镜像的时候直接使用ip，这次改为使用服务名：

FROM centos:7
    
    
    LABEL author=lsy
    
    
    ENV path=/usr/soft
    
    
    RUN mkdir ${path}
    
    
    WORKDIR ${path}
    
    
    ADD jdk-8u191-linux-x64.tar.gz ${path}
    
    
    ENV JAVA_HOME=${path}/jdk1.8.0_191
    ENV CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
    ENV PATH=$JAVA_HOME/bin:$PATH
    
    
    COPY k8s_demo-1.0.jar ${path}
    
    
    EXPOSE 8080
    
    
    CMD  java -jar -DredisIp=redis k8s_demo-1.0.jar

然后进行镜像构建：

![71e3b6ba8186e2e8ba30ac8ff4a256d0.png][]

然后改为使用当前镜像进行容器的构建，之后创建容器

END

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