k8s部署coredns

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    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。
    kubedns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KubeDNS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

准备工作

准备coredns的yaml文件

首先我们的查看cat /etc/kubernetes/kubelet dns的ip地址是多少，这里我的是10.254.0.2，根据自己的情况进行修改

  • 执行创建

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    # ./deploy.sh -i 10.254.0.2 | kubectl apply -f -
    serviceaccount/coredns created
    clusterrole.rbac.authorization.k8s.io/system:coredns created
    clusterrolebinding.rbac.authorization.k8s.io/system:coredns created
    configmap/coredns created
    deployment.apps/coredns created
    service/kube-dns created

  • 擦看coredns信息

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    # kubectl get pod,svc,deployment,rc -n kube-system|grep dns
    pod/coredns-799775f9b6-mgdc9                1/1     Running   0          12m
    pod/coredns-799775f9b6-v95lp                1/1     Running   0          12m
    service/kube-dns               ClusterIP   10.254.0.2       <none>        53/UDP,53/TCP,9153/TCP   12m

    deployment.extensions/coredns                2/2     2            2           12m

部署 DNS 自动扩容

    在大规模集群的情况下，可能需要集群 DNS 自动扩容，具体文档请参考 DNS Horizontal Autoscaler，DNS 扩容算法可参考 Github，如有需要请自行修改；以下为具体配置

  • dns-horizontal-autoscaler.yaml

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    kind: ServiceAccount
    apiVersion: v1
    metadata:
      name: kube-dns-autoscaler
      namespace: kube-system
      labels:
        addonmanager.kubernetes.io/mode: Reconcile
    ---
    kind: ClusterRole
    apiVersion: rbac.authorization.k8s.io/v1
    metadata:
      name: system:kube-dns-autoscaler
      labels:
        addonmanager.kubernetes.io/mode: Reconcile
    rules:
      - apiGroups: [""]
        resources: ["nodes"]
        verbs: ["list"]
      - apiGroups: [""]
        resources: ["replicationcontrollers/scale"]
        verbs: ["get", "update"]
      - apiGroups: ["extensions"]
        resources: ["deployments/scale", "replicasets/scale"]
        verbs: ["get", "update"]
    # Remove the configmaps rule once below issue is fixed:
    # kubernetes-incubator/cluster-proportional-autoscaler#16
      - apiGroups: [""]
        resources: ["configmaps"]
        verbs: ["get", "create"]
    ---
    kind: ClusterRoleBinding
    apiVersion: rbac.authorization.k8s.io/v1
    metadata:
      name: system:kube-dns-autoscaler
      labels:
        addonmanager.kubernetes.io/mode: Reconcile
    subjects:
      - kind: ServiceAccount
        name: kube-dns-autoscaler
        namespace: kube-system
    roleRef:
      kind: ClusterRole
      name: system:kube-dns-autoscaler
      apiGroup: rbac.authorization.k8s.io

    ---
    apiVersion: apps/v1
    kind: Deployment
    metadata:
      name: kube-dns-autoscaler
      namespace: kube-system
      labels:
        k8s-app: kube-dns-autoscaler
        kubernetes.io/cluster-service: "true"
        addonmanager.kubernetes.io/mode: Reconcile
    spec:
      selector:
        matchLabels:
          k8s-app: kube-dns-autoscaler
      template:
        metadata:
          labels:
            k8s-app: kube-dns-autoscaler
          annotations:
            scheduler.alpha.kubernetes.io/critical-pod: ''
        spec:
          priorityClassName: system-cluster-critical
          containers:
          - name: autoscaler
            image: gcr.azk8s.cn/google_containers/cluster-proportional-autoscaler-amd64:1.1.2-r2
            resources:
                requests:
                    cpu: "20m"
                    memory: "10Mi"
            command:
              - /cluster-proportional-autoscaler
              - --namespace=kube-system
              - --configmap=kube-dns-autoscaler
              # Should keep target in sync with cluster/addons/dns/kube-dns.yaml.base
              - --target=Deployment/coredns
              # When cluster is using large nodes(with more cores), "coresPerReplica" should dominate.
              # If using small nodes, "nodesPerReplica" should dominate.
              - --default-params={"linear":{"coresPerReplica":256,"nodesPerReplica":16,"preventSinglePointFailure":true}}
              - --logtostderr=true
              - --v=2
          tolerations:
          - key: "CriticalAddonsOnly"
            operator: "Exists"
          serviceAccountName: kube-dns-autoscaler

  • 执行创建

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    # kubectl apply -f dns-horizontal-autoscaler.yaml 
    serviceaccount/kube-dns-autoscaler created
    clusterrole.rbac.authorization.k8s.io/system:kube-dns-autoscaler created
    clusterrolebinding.rbac.authorization.k8s.io/system:kube-dns-autoscaler created
    deployment.apps/kube-dns-autoscaler created

执行创建以后我们可以看到pod 创建了两个dns

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# kubectl get pods -n kube-system|grep coredns
coredns-68676b6b88-pw9c2                1/1     Running   0          7m18s
coredns-68676b6b88-tgbbv                1/1     Running   0          100m
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