Kubernetes 1.5 配置dns

　　在kubernetes1.2的时候，采用了skydns + kube2dns +etcd的方式来部署dns。而从1.3开始，则部署方式有了一点儿变化，将skydns和kube2dns封装到了一个容器镜像中，放弃了etcd，而将dns解析直接放入到了内存之中，同时引入了dnsmasq，进一步利用其缓存，具体的原理，请查阅相关文档。本篇文档，主要阐述新版的dns在kubernetes中的具体部署。

　　在Kubernetes的源码目录中，有个cluster/addons/dns目录，下面有几个与dns相关的文件，我们将其中的skydns-rc.yaml.sed以及skydns-svc.yaml.sed文件下载到本地，并去掉后缀。只是拷贝文件的话，可以通过https://rawgit.com这个地址加速，如下：

wget https://rawgit.com/kubernetes/kubernetes/release-1.5/cluster/addons/dns/skydns-rc.yaml.sed -O skydns-rc.yaml
wget https://rawgit.com/kubernetes/kubernetes/release-1.5/cluster/addons/dns/skydns-svc.yaml.sed -O skydns-svc.yaml

下载下来的原文件是用于saltstack自动化安装的，我们手动处理的时候，需要进行相关修改。

修改skydns-rc.yaml内容如下：

# 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.

# TODO - At some point, we need to rename all skydns-*.yaml.* files to kubedns-*.yaml.*
# 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"
spec:
　#指定副本数
  replicas: 1
  # 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: ''
        scheduler.alpha.kubernetes.io/tolerations: '[{"key":"CriticalAddonsOnly", "operator":"Exists"}]'
    spec:
      containers:
      - name: kubedns
　　　　　#修改image地址，默认是google的仓库地址，如果不担心被墙，可以直接使用，我这里使用的私有仓库地址，如果要使用国内其他仓库地址，推荐使用阿里云镜像库
        image: myhub.fdccloud.com/library/kubedns-amd64:1.9
        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: /healthz-kubedns
            port: 8080
            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指定一级域名，可自定义
        - --domain=cluster.local.
        - --dns-port=10053
        - --config-map=kube-dns
　　　　 #增加--kube-master-url，指向kube master的地址
        - --kube-master-url=http://10.5.10.116:8080
        # This should be set to v=2 only after the new image (cut from 1.5) has
        # been released, otherwise we will flood the logs.
        - --v=0
        #__PILLAR__FEDERATIONS__DOMAIN__MAP__
        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
      - name: dnsmasq
        image: myhub.fdccloud.com/library/kube-dnsmasq-amd64:1.4
        livenessProbe:
          httpGet:
            path: /healthz-dnsmasq
            port: 8080
            scheme: HTTP
          initialDelaySeconds: 60
          timeoutSeconds: 5
          successThreshold: 1
          failureThreshold: 5
        args:
        - --cache-size=1000
        - --no-resolv
        - --server=127.0.0.1#10053
        #- --log-facility=-　　#注释掉该行
        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: 10Mi
      - name: dnsmasq-metrics
        image: myhub.fdccloud.com/library/dnsmasq-metrics-amd64:1.0
        livenessProbe:
          httpGet:
            path: /metrics
            port: 10054
            scheme: HTTP
          initialDelaySeconds: 60
          timeoutSeconds: 5
          successThreshold: 1
          failureThreshold: 5
        args:
        - --v=2
        - --logtostderr
        ports:
        - containerPort: 10054
          name: metrics
          protocol: TCP
        resources:
          requests:
            memory: 10Mi
      - name: healthz
        image: myhub.fdccloud.com/library/exechealthz-amd64:1.2
        resources:
          limits:
            memory: 50Mi
          requests:
            cpu: 10m
            # Note that this container shouldn't really need 50Mi of memory. The
            # limits are set higher than expected pending investigation on #29688.
            # The extra memory was stolen from the kubedns container to keep the
            # net memory requested by the pod constant.
            memory: 50Mi
        args:
        - --cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1 >/dev/null
        - --url=/healthz-dnsmasq
        - --cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1:10053 >/dev/null
        - --url=/healthz-kubedns
        - --port=8080
        - --quiet
        ports:
        - containerPort: 8080
          protocol: TCP
      dnsPolicy: Default  # Don't use cluster DNS.

修改skydns-svc.yaml内容如下：

# 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.

# TODO - At some point, we need to rename all skydns-*.yaml.* files to kubedns-*.yaml.*

# __MACHINE_GENERATED_WARNING__

apiVersion: v1
kind: Service
metadata:
  name: kube-dns
  namespace: kube-system
  labels:
    k8s-app: kube-dns
    kubernetes.io/cluster-service: "true"
    kubernetes.io/name: "KubeDNS"
spec:
  selector:
    k8s-app: kube-dns
  #指定clusterIP，后面各pod的dns地址都会指向该地址
  clusterIP: 10.254.0.100
  ports:
  - name: dns
    port: 53
    protocol: UDP
  - name: dns-tcp
    port: 53
    protocol: TCP

启动dns：

kubectl create -f skydns-rc.yaml
kubectl create -f skydns-svc.yaml

修改各node节点上的/etc/kubernetes/kubelet配置文件，增加如下行：

KUBELET_ARGS="--cluster_dns=10.254.0.100 --cluster_domain=cluster.local"

重启各节点：

systemctl restart kubelet

添加一个busybox的pod用于测试，busybox.yaml内容如下：

apiVersion: v1
kind: Pod
metadata:
  labels:
    name: busybox
    role: master
  name: busybox
spec:
  containers:
  - name: busybox
    image: myhub.fdccloud.com/library/busybox
    command:
    - sleep
    - "3600"

执行如下操作：

kubectl exec -it busybox sh
nslookup kubernetes
nslookup kubernetes.default.cluster.local
nslookup kubernetes.default.svc.cluster.local

如果能正常解析，则部署OK。