Kubernetes 部署集群内部DNS服务

Kubernetes 部署集群内部DNS服务

部署官网：https://github.com/kubernetes/kubernetes/tree/master/cluster/addons/dns/coredns

为服务提供名称域名的访问。

- DNS服务监视Kubernetes API，为每一个Service创建DNS记录用于域名解析。
- ClusterIP A记录格式：<service-name>.<namespace-name>.svc.cluster.local
示例：my-svc.my-namespace.svc.cluster.local

coredns

1、创建dns Yaml配置文件

apiVersion: v1
kind: ServiceAccount
metadata:
  name: coredns
  namespace: kube-system
  labels:
      kubernetes.io/cluster-service: "true"
      addonmanager.kubernetes.io/mode: Reconcile
---
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
---
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
        # 更改dns域
        kubernetes cluster.local in-addr.arpa ip6.arpa {
            pods insecure
            upstream
        }
        cache 30
        loop
        reload
        loadbalance
    }
---
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:
  # 2. Default is 1.
  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
        # 更改DNS地址
        image: coredns/coredns:1.2.6
        imagePullPolicy: IfNotPresent
        resources:
          limits:
            # 内存自定义
            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: ""
    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
  # 更改为kube配置的DNS地址
  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

vim coredns.yaml

2、执行命令创建dns

kubectl apply -f coredns.yaml 

3、查看pod状态

NAME READY STATUS RESTARTS AGE
coredns-6765c879f8-lwtwt 1/1 Running 0 25s

kubectl get pods -n kube-system

4、测试dns是否正常
4.1 启用一个临时容器

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

4.2 进入容器并进行解析

/ # nslookup kubernetes
/ # nslookup kubernetes
Server: 10.0.0.2
Address 1: 10.0.0.2 kube-dns.kube-system.svc.cluster.local

4.3 创建另一个容器测试

kubectl run -it --image=busybox:1.28.4 --rm --restart=Never sh -n kube-system
/ # nslookup my-service.default
Server: 10.0.0.2
Address 1: 10.0.0.2 kube-dns.kube-system.svc.cluster.local

Name: my-service.default
Address 1: 10.0.0.123 my-service.default.svc.cluster.local

查看已有解析service

kubectl get ep
NAME ENDPOINTS AGE
kubernetes 192.168.1.108:6443,192.168.1.109:6443 3d
my-service <none> 7h54m
nginx-service 172.17.1.2:80,172.17.1.3:80,172.17.1.6:80 2d4h
nginx-service2 <none> 25h

# 注意事项
注：在api的service证书签发内留下dns的ip地址
# 报错：Failed to list *v1.Namespace: Get https://10.0.0.1:443/api/v1/namespaces?limit=500&resourceVersion=0: dial tcp 10.0.0.1:443: i/o timeout
解决方案：重启Node上的kube-proxy、重新创建coredns。