Kube-dns是一种易于使用的解决方案，用于在Kubernetes集群中提供DNS服务。本文章将指导您完成在群集中安装kube-dns的过程，以及测试DNS设置以确保其正常工作。完成后，您应该在群集中安装有效的kube-dns，并且pod应该能够成功使用您的DNS。

• 安装kube-dns
• 验证kube-dns pod是否正确启动
• 测试kube-dns
• 故障排错

安装kube-dns

• 准备kube-dns.yaml配置文件

# Copyright 2016 The Kubernetes Authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

apiVersion: v1
kind: Service
metadata:
  name: kube-dns
  namespace: kube-system
  labels:
    k8s-app: kube-dns
    kubernetes.io/cluster-service: "true"
    addonmanager.kubernetes.io/mode: Reconcile
    kubernetes.io/name: "KubeDNS"
spec:
  selector:
    k8s-app: kube-dns
  clusterIP: 10.32.0.10
  ports:
  - name: dns
    port: 53
    protocol: UDP
  - name: dns-tcp
    port: 53
    protocol: TCP
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: kube-dns
  namespace: kube-system
  labels:
    kubernetes.io/cluster-service: "true"
    addonmanager.kubernetes.io/mode: Reconcile
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: kube-dns
  namespace: kube-system
  labels:
    addonmanager.kubernetes.io/mode: EnsureExists
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: kube-dns
  namespace: kube-system
  labels:
    k8s-app: kube-dns
    kubernetes.io/cluster-service: "true"
    addonmanager.kubernetes.io/mode: Reconcile
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:
    rollingUpdate:
      maxSurge: 10%
      maxUnavailable: 0
  selector:
    matchLabels:
      k8s-app: kube-dns
  template:
    metadata:
      labels:
        k8s-app: kube-dns
      annotations:
        scheduler.alpha.kubernetes.io/critical-pod: ''
    spec:
      tolerations:
      - key: "CriticalAddonsOnly"
        operator: "Exists"
      volumes:
      - name: kube-dns-config
        configMap:
          name: kube-dns
          optional: true
      containers:
      - name: kubedns
        image: registry.cn-hangzhou.aliyuncs.com/google_containers/k8s-dns-kube-dns-amd64:1.14.7
        resources:
          # TODO: Set memory limits when we've profiled the container for large
          # clusters, then set request = limit to keep this container in
          # guaranteed class. Currently, this container falls into the
          # "burstable" category so the kubelet doesn't backoff from restarting it.
          limits:
            memory: 170Mi
          requests:
            cpu: 100m
            memory: 70Mi
        livenessProbe:
          httpGet:
            path: /healthcheck/kubedns
            port: 10054
            scheme: HTTP
          initialDelaySeconds: 60
          timeoutSeconds: 5
          successThreshold: 1
          failureThreshold: 5
        readinessProbe:
          httpGet:
            path: /readiness
            port: 8081
            scheme: HTTP
          # we poll on pod startup for the Kubernetes master service and
          # only setup the /readiness HTTP server once that's available.
          initialDelaySeconds: 3
          timeoutSeconds: 5
        args:
        - --domain=cluster.local.
        - --dns-port=10053
        - --config-dir=/kube-dns-config
        - --v=2
        env:
        - name: PROMETHEUS_PORT
          value: "10055"
        ports:
        - containerPort: 10053
          name: dns-local
          protocol: UDP
        - containerPort: 10053
          name: dns-tcp-local
          protocol: TCP
        - containerPort: 10055
          name: metrics
          protocol: TCP
        volumeMounts:
        - name: kube-dns-config
          mountPath: /kube-dns-config
      - name: dnsmasq
        image: registry.cn-hangzhou.aliyuncs.com/google_containers/k8s-dns-dnsmasq-nanny-amd64:1.14.7
        livenessProbe:
          httpGet:
            path: /healthcheck/dnsmasq
            port: 10054
            scheme: HTTP
          initialDelaySeconds: 60
          timeoutSeconds: 5
          successThreshold: 1
          failureThreshold: 5
        args:
        - -v=2
        - -logtostderr
        - -configDir=/etc/k8s/dns/dnsmasq-nanny
        - -restartDnsmasq=true
        - --
        - -k
        - --cache-size=1000
        - --no-negcache
        - --log-facility=-
        - --server=/cluster.local/127.0.0.1#10053
        - --server=/in-addr.arpa/127.0.0.1#10053
        - --server=/ip6.arpa/127.0.0.1#10053
        ports:
        - containerPort: 53
          name: dns
          protocol: UDP
        - containerPort: 53
          name: dns-tcp
          protocol: TCP
        # see: https://github.com/kubernetes/kubernetes/issues/29055 for details
        resources:
          requests:
            cpu: 150m
            memory: 20Mi
        volumeMounts:
        - name: kube-dns-config
          mountPath: /etc/k8s/dns/dnsmasq-nanny
      - name: sidecar
        image: registry.cn-hangzhou.aliyuncs.com/google_containers/k8s-dns-sidecar-amd64:1.14.7
        livenessProbe:
          httpGet:
            path: /metrics
            port: 10054
            scheme: HTTP
          initialDelaySeconds: 60
          timeoutSeconds: 5
          successThreshold: 1
          failureThreshold: 5
        args:
        - --v=2
        - --logtostderr
        - --probe=kubedns,127.0.0.1:10053,kubernetes.default.svc.cluster.local,5,SRV
        - --probe=dnsmasq,127.0.0.1:53,kubernetes.default.svc.cluster.local,5,SRV
        ports:
        - containerPort: 10054
          name: metrics
          protocol: TCP
        resources:
          requests:
            memory: 20Mi
            cpu: 10m
      dnsPolicy: Default  # Don't use cluster DNS.
      serviceAccountName: kube-dns

注意修改你的这个参数 clusterIP: 10.32.0.10

• 安装kube-dns

kubectl create -f kube-dns.yaml

验证kube-dns pod是否正确启动

kubectl get pods -l k8s-app=kube-dns -n kube-system

• 你应该得到显示kube-dns pod的输出。它应该看起来像这样：

NAME                        READY     STATUS    RESTARTS   AGE
kube-dns-598d7bf7d4-spbmj   3/3       Running   0          36s

确保3/3容器已准备就绪，并且pod的状态为Running,可能需要一段时间才能完全启动并运行，因此如果READY首先不是3/3，请稍后再检查。

测试kube-dns

• 首先，我们需要启动一个可用于测试的pod：

kubectl run busybox --image=busybox:1.28 --command -- sleep 3600
POD_NAME=$(kubectl get pods -l run=busybox -o jsonpath="{.items[0].metadata.name}")

• 接下来，从busybox容器中运行一个nslookup

kubectl exec -ti $POD_NAME -- nslookup kubernetes

• 您应该得到如下所示的输出：

Server:    10.32.0.10
Address 1: 10.32.0.10 kube-dns.kube-system.svc.cluster.local
Name:      kubernetes
Address 1: 10.32.0.1 kubernetes.default.svc.cluster.local

• 如果nslookup成功，那么你的kube-dns安装正在运行！

故障排错

• 我在做最后一步测试的时候，nslookup的时候，报错了，解析失败了

[root@k8s-master example]# kubectl exec -ti busybox -- nslookup kubernetes.default
Server:    10.254.0.2
Address 1: 10.254.0.2

nslookup: can't resolve 'kubernetes.default'
command terminated with exit code 1

查看kube-dns的相关信息，找出了错误的所在，实在粗心大意

[root@k8s-master example]# kubectl exec busybox cat /etc/resolv.conf
nameserver 10.254.0.11
search default.svc.cluster.local svc.cluster.local cluster.local nhcdru4itrfetijnzscjvd1jna.ax.internal.chinacloudapp.cn
options ndots:5
[root@k8s-master example]# kubectl get pod -n kube-system
NAME                        READY     STATUS    RESTARTS   AGE
kube-dns-6db447cbfc-2zmrr   3/3       Running   0          23m
[root@k8s-master example]# kubectl get ep kube-dns --namespace=kube-system
NAME       ENDPOINTS                     AGE
kube-dns   172.17.0.2:53,172.17.0.2:53   25m
[root@k8s-master example]# kubectl get svc --namespace=kube-system
NAME       TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)         AGE
kube-dns   ClusterIP   10.254.0.2           53/UDP,53/TCP   25m

• 发现容器里面指定的nameserver为10.254.0.11，但是我的dns服务的ip地址是10.254.0.2，这样不一致肯定解析失败了。最终通过修改kube-dns.yaml，中的clusterIP: 参数，修改为10.254.0.11，并重新构建了kube-dns服务，最终顺利解析。