【好文收藏】K8S集群部署CoreDNS服务

Dear 丶 2023-10-05 19:10 12阅读 0赞

## K8S集群部署CoreDNS服务 ##

> k8s集群中的应用通常是通过ingress实现微服务发布的，前文介绍过在K8S集群中使用traefik实现服务的自动发布，其实现方式是traefik通过集群的DNS服务来解析service对应的集群地址（clusterip），从而将用户的访问请求转发到集群地址上。因此，在部署完集群后的第一件事情应该是配置DNS服务，目前可选的方案有skydns, kube-dns, coredns。
> 
> kube-dns是Kubernetes中的一个内置插件，目前作为一个独立的开源项目维护，见https://github.com/kubernetes/dns。该DNS服务器利用SkyDNS的库来为Kubernetes pod和服务提供DNS请求。
> 
> CoreDNS项目是SkyDNS2的作者，Miek Gieben采用更模块化，可扩展的框架构建,将此DNS服务器作为Kube-DNS的替代品。CoreDNS作为CNCF中的托管的一个项目，在Kuberentes1.9版本中，使用kubeadm方式安装的集群可以通过以下命令直接安装CoreDNS。  
> kubeadm init --feature-gates=CoreDNS=true。  
> 本文将介绍coredns的配置

关于在1.5.2 rpm集群版本上配置skydns服务请参考：  
https://blog.51cto.com/ylw6006/2067923

关于traefik实现微服务发布请参考：  
https://blog.51cto.com/ylw6006/2072667  
https://blog.51cto.com/ylw6006/2073718

关于kube-dns的详细介绍可以参考大牛博客：  
https://jimmysong.io/posts/configuring-kubernetes-kube-dns/

一、准备yaml配置文件  
1、coredns-sa.yaml文件，创建ServiceAccount

# cat coredns-sa.yaml 
    apiVersion: v1
    kind: ServiceAccount
    metadata:
      name: coredns
      namespace: kube-system
      labels:
          kubernetes.io/cluster-service: "true"
          addonmanager.kubernetes.io/mode: Reconcile

2、coredns-rbac.yaml文件，创建rbac ClusterRole和ClusterRoleBinding

# cat coredns-rbac.yaml 
    apiVersion: rbac.authorization.k8s.io/v1
    kind: ClusterRole
    metadata:
      labels:
        kubernetes.io/bootstrapping: rbac-defaults
        addonmanager.kubernetes.io/mode: Reconcile
      name: system:coredns
    rules:
    - apiGroups:
      - ""
      resources:
      - endpoints
      - services
      - pods
      - namespaces
      verbs:
      - list
      - watch
    ---
    apiVersion: rbac.authorization.k8s.io/v1
    kind: ClusterRoleBinding
    metadata:
      annotations:
        rbac.authorization.kubernetes.io/autoupdate: "true"
      labels:
        kubernetes.io/bootstrapping: rbac-defaults
        addonmanager.kubernetes.io/mode: EnsureExists
      name: system:coredns
    roleRef:
      apiGroup: rbac.authorization.k8s.io
      kind: ClusterRole
      name: system:coredns
    subjects:
    - kind: ServiceAccount
      name: coredns
      namespace: kube-system

3、coredns-configmap.yaml文件，定义Corefile配置文件的参数配置

# cat coredns-configmap.yaml 
    apiVersion: v1
    kind: ConfigMap
    metadata:
      name: coredns
      namespace: kube-system
    data:
      Corefile: |
        .:53 {
            errors
            log
            health
            kubernetes cluster.local 10.254.0.0/18
            proxy . /etc/resolv.conf
            cache 30
        }

4、coredns-deployment.yaml文件，定义pod的创建模板

# cat coredns-deployment.yaml 
    apiVersion: extensions/v1beta1
    kind: Deployment
    metadata:
      name: coredns
      namespace: kube-system
      labels:
        k8s-app: coredns
        kubernetes.io/cluster-service: "true"
        kubernetes.io/name: "CoreDNS"
    spec:
      replicas: 1
      selector:
        matchLabels:
          k8s-app: coredns
      template:
        metadata:
          labels:
            k8s-app: coredns
          annotations:
            scheduler.alpha.kubernetes.io/critical-pod: ''
            scheduler.alpha.kubernetes.io/tolerations: '[{"key":"CriticalAddonsOnly", "operator":"Exists"}]'
        spec:
          serviceAccountName: coredns
          containers:
          - name: coredns
            image: coredns/coredns:latest
            imagePullPolicy: Always
            args: [ "-conf", "/etc/coredns/Corefile" ]
            volumeMounts:
            - name: config-volume
              mountPath: /etc/coredns
            ports:
            - containerPort: 53
              name: dns
              protocol: UDP
            - containerPort: 53
              name: dns-tcp
              protocol: TCP
            livenessProbe:
              httpGet:
                path: /health
                port: 8080
                scheme: HTTP
              initialDelaySeconds: 60
              timeoutSeconds: 5
              successThreshold: 1
              failureThreshold: 5
          dnsPolicy: Default
          volumes:
            - name: config-volume
              configMap:
                name: coredns
                items:
                - key: Corefile
                  path: Corefile

5、 coredns-service.yaml文件，定义服务的名称

# cat coredns-service.yaml 
    apiVersion: v1
    kind: Service
    metadata:
      name: coredns
      namespace: kube-system
      labels:
        k8s-app: coredns
        kubernetes.io/cluster-service: "true"
        kubernetes.io/name: "CoreDNS"
    spec:
      selector:
        k8s-app: coredns
      clusterIP: 10.254.0.2
      ports:
      - name: dns
        port: 53
        protocol: UDP
      - name: dns-tcp
        port: 53
    protocol: TCP

二、通过yaml配置文件创建coredns

# kubectl get node
    # kubectl get pod,svc,deployment,rc
    # kubectl get pod,svc,deployment,rc -n kube-system
    # cd yaml/coredns/
    # ls -l
    # kubectl create -f .

![K8S集群部署Coredns服务][K8S_Coredns]

# kubectl get pod,svc,deployment,rc -n kube-system

![K8S集群部署Coredns服务][K8S_Coredns 1]  
三、创建一个nginx服务用于测试

# kubectl create -f .
    # kubectl get pod,svc,deployment,rc 
    # kubectl run -i --tty busybox --image=registry.59iedu.com/busybox /bin/sh

![K8S集群部署Coredns服务][K8S_Coredns 2]

参考链接：

[https://blog.51cto.com/ylw6006/2108426][https_blog.51cto.com_ylw6006_2108426]

[K8S_Coredns]: https://img-blog.csdnimg.cn/img_convert/de3ad34a325dc92dceb2ddcc14d84cbb.png
[K8S_Coredns 1]: https://img-blog.csdnimg.cn/img_convert/49e46d4efde3521bf9a80745e95e5e3d.png
[K8S_Coredns 2]: https://img-blog.csdnimg.cn/img_convert/18ab31350f7627367c10f4b5c9da88fb.png
[https_blog.51cto.com_ylw6006_2108426]: https://blog.51cto.com/ylw6006/2108426