k8s-集群内部域名访问coredns

太过爱你忘了你带给我的痛 2022-02-05 08:15 1138阅读 0赞

![在这里插入图片描述][20190505112602148.png]  
集群内部的DNS服务，来为service提供DNS名称的访问。  
（CoreDNS、Kube-DNS，由于kube-dns设计复杂，不易维护，默认dns是coreDNS）  
[coreDNS官方文档所在地][coreDNS].下载文件 coredns.yaml.sed

# serviceaccount，利用pod来访问apiserver
    apiVersion: v1
    kind: ServiceAccount
    metadata:
      name: coredns
      namespace: kube-system
      labels:
          kubernetes.io/cluster-service: "true"
          addonmanager.kubernetes.io/mode: Reconcile
    ---
    # 赋予ServiceAccount访问权限
    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
    - apiGroups:
      - ""
      resources:
      - nodes
      verbs:
      - get
    ---
    # 把权限绑定到具体的ServiceAccount
    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
    ---
    apiVersion: v1
    kind: ConfigMap
    metadata:
      name: coredns
      namespace: kube-system
      labels:
          addonmanager.kubernetes.io/mode: EnsureExists
    data:
      Corefile: | .:53 { errors health kubernetes $DNS_DOMAIN in-addr.arpa ip6.arpa { pods insecure upstream fallthrough in-addr.arpa ip6.arpa ttl 30 } prometheus :9153 forward . /etc/resolv.conf cache 30 loop reload loadbalance }
    # $DNS_DOMAIN替换：cluster.local，参见cat /opt/kubernetes/cfg/kubelet.config中的clusterDomain: cluster.local.
    ---
    apiVersion: apps/v1
    kind: Deployment
    metadata:
      name: coredns
      namespace: kube-system
      labels:
        k8s-app: kube-dns
        kubernetes.io/cluster-service: "true"
        addonmanager.kubernetes.io/mode: Reconcile
        kubernetes.io/name: "CoreDNS"
    spec:
      # replicas: not specified here:
      # 1. In order to make Addon Manager do not reconcile this replicas parameter.
      # 2. Default is 1.
      # 3. Will be tuned in real time if DNS horizontal auto-scaling is turned on.
      strategy:
        type: RollingUpdate
        rollingUpdate:
          maxUnavailable: 1
      selector:
        matchLabels:
          k8s-app: kube-dns
      template:
        metadata:
          labels:
            k8s-app: kube-dns
          annotations:
            seccomp.security.alpha.kubernetes.io/pod: 'docker/default'
        spec:
          priorityClassName: system-cluster-critical
          serviceAccountName: coredns
          tolerations:
            - key: "CriticalAddonsOnly"
              operator: "Exists"
          nodeSelector:
            beta.kubernetes.io/os: linux
          containers:
          - name: coredns
            image: k8s.gcr.io/coredns:1.3.1
            # 修改image: coredns/coredns:1.3.1
            imagePullPolicy: IfNotPresent
            resources:
              limits:
                memory: 170Mi
              requests:
                cpu: 100m
                memory: 70Mi
            args: [ "-conf", "/etc/coredns/Corefile" ]
            volumeMounts:
            - name: config-volume
              mountPath: /etc/coredns
              readOnly: true
            ports:
            - containerPort: 53
              name: dns
              protocol: UDP
            - containerPort: 53
              name: dns-tcp
              protocol: TCP
            - containerPort: 9153
              name: metrics
              protocol: TCP
            livenessProbe:
              httpGet:
                path: /health
                port: 8080
                scheme: HTTP
              initialDelaySeconds: 60
              timeoutSeconds: 5
              successThreshold: 1
              failureThreshold: 5
            readinessProbe:
              httpGet:
                path: /health
                port: 8080
                scheme: HTTP
            securityContext:
              allowPrivilegeEscalation: false
              capabilities:
                add:
                - NET_BIND_SERVICE
                drop:
                - all
              readOnlyRootFilesystem: true
          dnsPolicy: Default
          volumes:
            - name: config-volume
              configMap:
                name: coredns
                items:
                - key: Corefile
                  path: Corefile
    ---
    apiVersion: v1
    kind: Service
    metadata:
      name: kube-dns
      namespace: kube-system
      annotations:
        prometheus.io/port: "9153"
        prometheus.io/scrape: "true"
      labels:
        k8s-app: kube-dns
        kubernetes.io/cluster-service: "true"
        addonmanager.kubernetes.io/mode: Reconcile
        kubernetes.io/name: "CoreDNS"
    spec:
      selector:
        k8s-app: kube-dns
      clusterIP: $DNS_SERVER_IP
      # 参见cat /opt/kubernetes/cfg/kubelet.config中的clusterDNS:，此处改为
      # clusterIP: 10.0.0.2
      ports:
      - name: dns
        port: 53
        protocol: UDP
      - name: dns-tcp
        port: 53
        protocol: TCP
      - name: metrics
        port: 9153
        protocol: TCP

![在这里插入图片描述][20190505155431519.png]  
测试coredns

kubectl run -it --image=busybox:1.28.4 --rm --restart=Never sh

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTA4MDE5OTQ_size_16_color_FFFFFF_t_70]  
DNS服务监控Kubernetes API，为每一个Service创建DNS记录用于域名解析。  
ClusterIP 记录格式(**具体实例见上截图展示**)：

<service-name>.<namespace-name>.svc.cluster.local

另外，可以在别的命名空间中解析域名  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTA4MDE5OTQ_size_16_color_FFFFFF_t_70 1]  
由**nslookup my-service** 修改为 **nslookup my-service.default**即可实现解析。

[20190505112602148.png]: /images/20220205/570d3fa7dd4f4cf480693967f2a3267a.png
[coreDNS]: https://github.com/kubernetes/kubernetes/tree/master/cluster/addons/dns/coredns
[20190505155431519.png]: /images/20220205/926f90bad46c45e193cf86ecee4bc91d.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTA4MDE5OTQ_size_16_color_FFFFFF_t_70]: /images/20220205/5081d890963041e0b1fb8c71f9517adb.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTA4MDE5OTQ_size_16_color_FFFFFF_t_70 1]: /images/20220205/ae4c00b29d124ee8806b2eb244fa9d2c.png