kube-dns部署

Posted 2020-11-03

一，基本概念

    kube-dns主要实现K8S集群内部服务发现以及集群内部通过服务名进行访问。kubernetes集群中的服务都会有一个只用于内部访问的ClusterIP，如下：

[[email protected] ~]# kubectl get svc
NAME         TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)         AGE
kubernetes   ClusterIP   10.254.0.1       <none>        443/TCP         54d
mysql        NodePort    10.254.194.156   <none>        3306:8606/TCP   1d
myweb        NodePort    10.254.244.155   <none>        8080:8500/TCP   20h

    kube-dns可以实现集群内部的服务名与ClusterIP的解析，实现服务之间通过服务名的访问，方便部署管理

    kubernetes提供的虚拟DNS服务1.6版本之后主要由kube-dns，dnsmasq，sidecar等3个容器组成。其中kube-dns监控kubernetes服务资源，并将记录缓存至内存中；dnsmasq从kube-dns中获取集群服务的DNS记录并向集群提供DNS服务，sidecar负责另外两个容器的健康监测。

二，安装部署

    安装部署需要的yaml文件可以参考官网的github地址：https://github.com/kubernetes/kubernetes/tree/release-1.8/cluster/addons/dns；需要部署的文件为：kubedns-cm.yaml，kubedns-controller.yaml，kubedns-sa.yaml，kubedns-svc.yaml等

    其中kubedns-cm.yaml，kubedns-sa.yaml两个文件不需要更改，可以直接部署

    文件内容如下：

[[email protected] dns]# cat kubedns-cm.yaml 
apiVersion: v1
kind: ConfigMap
metadata:
  name: kube-dns
  namespace: kube-system
  labels:
    addonmanager.kubernetes.io/mode: EnsureExists
    
[[email protected] dns]# cat kubedns-sa.yaml
apiVersion: v1
kind: ServiceAccount
metadata:
  name: kube-dns
  namespace: kube-system
  labels:
    kubernetes.io/cluster-service: "true"
    addonmanager.kubernetes.io/mode: Reconcile

    kubedns-controller.yaml文件修改后如下

# 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.
#
# # Should keep target in cluster/addons/dns-horizontal-autoscaler/dns-horizontal-autoscaler.yaml
# # in sync with this file.
#
# # __MACHINE_GENERATED_WARNING__
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: gcr.io/google_containers/k8s-dns-kube-dns-amd64:1.14.4    
        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: gcr.io/google_containers/k8s-dns-dnsmasq-nanny-amd64:1.14.4 
        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
        - --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: gcr.io/google_containers/k8s-dns-sidecar-amd64:1.14.4 
        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,A
        - --probe=dnsmasq,127.0.0.1:53,kubernetes.default.svc.cluster.local,5,A
        ports:
        - containerPort: 10054
          name: metrics
          protocol: TCP
        resources:
          requests:
            memory: 20Mi
            cpu: 10m
      dnsPolicy: Default  # Don't use cluster DNS.
      serviceAccountName: kube-dns

    需要修改的地方：

        1）3个容器的镜像根据自身条件定义

        2）原文中变量  '_PILLAR__DNS__DOMAIN__'更改为自己设定的域名，通常为cluster.local

    

    kubedns-svc.yaml文件内容如下：

[[email protected] dns]# cat kubedns-svc.yaml 
# 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.
#
# # __MACHINE_GENERATED_WARNING__
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: 10.254.0.2
  ports:
  - name: dns
    port: 53
    protocol: UDP
  - name: dns-tcp
    port: 53
    protocol: TCP

    此文件只需要修改其中clusterIP，将kube-dns服务的clusterIP固定，可自行定义为kube-apiserver配置中--service-cluster-ip-range定义的IP段内的任意IP

    4个文件都生成之后则可以启动了

kubectl create -f kubedns-cm.yaml -f kubedns-sa.yaml -f  kubedns-controller.yaml -f kubedns-svc.yaml

    启动上述文件之后，还需要在kubelet配置中添加参数，指定DNS服务器：

 ...
  --cluster-dns=10.254.0.2   --cluster-domain=cluster.local
 ...

     之后就可以在集群之间使用服务名互相访问了

注意：

    kube-dns按照上述文件进行配置只有1个副本，如果需要生成多个副本官网推荐以下两种方案：

    1）参考https://github.com/kubernetes/kubernetes/tree/release-1.8/cluster/addons/dns-horizontal-autoscaler 

    2）使用命令：kubectl --namespace=kube-system scale deployment kube-dns --replicas=<NUM_YOU_WANT>