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Code  ›  kubenetes集群部署CoreDNS - DevOps海洋的渔夫
devops 集群服务器 dns kubernetes
https://www.jianshu.com/p/e7ea9e0e690b
我去
6 年前

为什么要解决这个问题呢？

因为kuberntes中的所有pod都是基于service域名解析后，再负载均衡分发到service后端的各个pod服务中，那么如果没有DNS解析，则无法查到各个服务对应的service服务，以下举个例子。

1.首先上传一个基于centos的工具镜像 

[root@server81 registry]# docker push 172.16.5.181:5000/networkbox
The push refers to repository [172.16.5.181:5000/networkbox]
6793eb3b0692: Pushed 
4b398ee02e06: Pushed 
b91100adb338: Pushed 
5f70bf18a086: Pushed 
479d1ea9f888: Pushed 
latest: digest: sha256:0159b2282815ecd59809dcca4d74cffd5b75a9ca5deec8a220080c254cc43ff2 size: 1987
[root@server81 registry]# 

2.创建pod以及svc


[root@server81 test_yaml]# vim networkbox.yaml 
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: networkbox
  labels:
    app: networkbox
spec:
  replicas: 10
  template:
    metadata:
      labels:
        app: networkbox
    spec:
      terminationGracePeriodSeconds: 60
      containers:
      - name: networkbox
        image: 172.16.5.181:5000/networkbox
apiVersion: v1
kind: Service
metadata:
  name: networkbox
  labels:
    name: networkbox
spec:
  ports:
  - port: 8008
  selector:
    name: networkbox
[root@server81 test_yaml]# vim networkbox.yaml 
[root@server81 test_yaml]# 
[root@server81 test_yaml]# kubectl apply -f networkbox.yaml 
deployment.extensions/networkbox configured
service/networkbox unchanged
[root@server81 test_yaml]# 
[root@server81 test_yaml]# kubectl get pod -o wide
NAME                          READY     STATUS        RESTARTS   AGE       IP           NODE
networkbox-85bd85cd54-7hsgp   1/1       Terminating   0          1m        10.1.0.196   172.16.5.181
networkbox-85bd85cd54-7sr5f   1/1       Terminating   0          1m        10.1.0.65    172.16.5.87
networkbox-85bd85cd54-9j8cg   1/1       Running       0          1m        10.1.0.194   172.16.5.181
networkbox-85bd85cd54-btcvz   1/1       Terminating   0          1m        10.1.0.198   172.16.5.181
networkbox-85bd85cd54-btmwm   1/1       Terminating   0          1m        10.1.0.200   172.16.5.181
networkbox-85bd85cd54-dfngz   1/1       Terminating   0          1m        10.1.0.197   172.16.5.181
networkbox-85bd85cd54-gp525   1/1       Terminating   0          1m        10.1.0.66    172.16.5.87
networkbox-85bd85cd54-llrw6   1/1       Running       0          1m        10.1.0.193   172.16.5.181
networkbox-85bd85cd54-psh4r   1/1       Running       0          1m        10.1.0.195   172.16.5.181
networkbox-85bd85cd54-zsg8m   1/1       Terminating   0          1m        10.1.0.199   172.16.5.181
[root@server81 test_yaml]# 
[root@server81 test_yaml]# kubectl get svc
NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
kubernetes   ClusterIP   10.0.6.1     <none>        443/TCP    1h
networkbox   ClusterIP   10.0.6.138   <none>        8008/TCP   1m
[root@server81 test_yaml]# 

3.进入networkbox的容器内，ping service域名，确认是否返回IP地址


[root@server81 test_yaml]# kubectl get svc
NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
kubernetes   ClusterIP   10.0.6.1     <none>        443/TCP    1h
networkbox   ClusterIP   10.0.6.138   <none>        8008/TCP   1m
[root@server81 test_yaml]# 
[root@server81 test_yaml]# kubectl exec -it networkbox-85bd85cd54-9j8cg bash
[root@networkbox-85bd85cd54-9j8cg /]# 
[root@networkbox-85bd85cd54-9j8cg /]# ping networkbox
ping: unknown host networkbox
[root@networkbox-85bd85cd54-9j8cg /]# 
[root@networkbox-85bd85cd54-9j8cg /]# ping kubernetes
ping: unknown host kubernetes
[root@networkbox-85bd85cd54-9j8cg /]# 

可以看出在容器内由于没有kubernetes的DNS服务解析，容器是找不到service的IP地址，那么也就找不到后面的服务了，所以CoreDNS的解析服务是必须要安装好的。

    rbac.authorization.kubernetes.io/autoupdate: "true"
  labels:
    kubernetes.io/bootstrapping: rbac-defaults
  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
data:
  Corefile: |
    .:53 {
        errors
        health
        kubernetes CLUSTER_DOMAIN REVERSE_CIDRS {
          pods insecure
          upstream
          fallthrough in-addr.arpa ip6.arpa
        }FEDERATIONS
        prometheus :9153
        proxy . UPSTREAMNAMESERVER
        cache 30
        reload
        loadbalance
    }STUBDOMAINS
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: coredns
  namespace: kube-system
  labels:
    k8s-app: kube-dns
    kubernetes.io/name: "CoreDNS"
spec:
  replicas: 2
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxUnavailable: 1
  selector:
    matchLabels:
      k8s-app: kube-dns
  template:
    metadata:
      labels:
        k8s-app: kube-dns
    spec:
      serviceAccountName: coredns
      tolerations:
        - key: node-role.kubernetes.io/master
          effect: NoSchedule
        - key: "CriticalAddonsOnly"
          operator: "Exists"
      containers:
      - name: coredns
        image: coredns/coredns:1.2.2
        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
        securityContext:
          allowPrivilegeEscalation: false
          capabilities:
            - NET_BIND_SERVICE
            drop:
            - all
          readOnlyRootFilesystem: true
        livenessProbe:
          httpGet:
            path: /health
            port: 8080
            scheme: HTTP
          initialDelaySeconds: 60
          timeoutSeconds: 5
          successThreshold: 1
          failureThreshold: 5
      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"
    kubernetes.io/name: "CoreDNS"
spec:
  selector:
    k8s-app: kube-dns
  clusterIP: CLUSTER_DNS_IP
  ports:
  - name: dns
    port: 53
    protocol: UDP
  - name: dns-tcp
    port: 53
    protocol: TCP

下载deploy.sh部署配置脚本。


#!/bin/bash
# Deploys CoreDNS to a cluster currently running Kube-DNS.
show_help () {
cat << USAGE
usage: $0 [ -r REVERSE-CIDR ] [ -i DNS-IP ] [ -d CLUSTER-DOMAIN ] [ -t YAML-TEMPLATE ] [ -k KUBECONFIG ]
    -r : Define a reverse zone for the given CIDR. You may specifcy this option more
         than once to add multiple reverse zones. If no reverse CIDRs are defined,
         then the default is to handle all reverse zones (i.e. in-addr.arpa and ip6.arpa)
    -i : Specify the cluster DNS IP address. If not specificed, the IP address of
         the existing "kube-dns" service is used, if present.
    -s : Skips the translation of kube-dns configmap to the corresponding CoreDNS Corefile configuration.
USAGE
exit 0
# Simple Defaults
CLUSTER_DOMAIN=cluster.local
YAML_TEMPLATE=`pwd`/coredns.yaml.sed
STUBDOMAINS=""
UPSTREAM=\\/etc\\/resolv\.conf
FEDERATIONS=""
# Translates the kube-dns ConfigMap to equivalent CoreDNS Configuration.
function translate-kube-dns-configmap {
    kube-dns-federation-to-coredns
    kube-dns-upstreamnameserver-to-coredns
    kube-dns-stubdomains-to-coredns
function kube-dns-federation-to-coredns {
  fed=$(kubectl -n kube-system get configmap kube-dns  -ojsonpath='{.data.federations}' 2> /dev/null | jq . | tr -d '":,')
  if [[ ! -z ${fed} ]]; then
  FEDERATIONS=$(sed -e '1s/^/federation /' -e 's/^/        /' -e '1i\\' <<< "${fed}") # add federation to the stanza
function kube-dns-upstreamnameserver-to-coredns {
  up=$(kubectl -n kube-system get configmap kube-dns  -ojsonpath='{.data.upstreamNameservers}' 2> /dev/null | tr -d '[",]')
  if [[ ! -z ${up} ]]; then
    UPSTREAM=${up}
function kube-dns-stubdomains-to-coredns {
  STUBDOMAIN_TEMPLATE='
    SD_DOMAIN:53 {
      errors
      cache 30
      proxy . SD_DESTINATION
  function dequote {
    str=${1#\"} # delete leading quote
    str=${str%\"} # delete trailing quote
    echo ${str}
  function parse_stub_domains() {
    sd=$1
  # get keys - each key is a domain
  sd_keys=$(echo -n $sd | jq keys[])
  # For each domain ...
  for dom in $sd_keys; do
    dst=$(echo -n $sd | jq '.['$dom'][0]') # get the destination
    dom=$(dequote $dom)
    dst=$(dequote $dst)
    sd_stanza=${STUBDOMAIN_TEMPLATE/SD_DOMAIN/$dom} # replace SD_DOMAIN
    sd_stanza=${sd_stanza/SD_DESTINATION/$dst} # replace SD_DESTINATION
    echo "$sd_stanza"
  sd=$(kubectl -n kube-system get configmap kube-dns  -ojsonpath='{.data.stubDomains}' 2> /dev/null)
  STUBDOMAINS=$(parse_stub_domains "$sd")
# Get Opts
while getopts "hsr:i:d:t:k:" opt; do
    case "$opt" in
    h)  show_help
    s)  SKIP=1
    r)  REVERSE_CIDRS="$REVERSE_CIDRS $OPTARG"
    i)  CLUSTER_DNS_IP=$OPTARG
    d)  CLUSTER_DOMAIN=$OPTARG
    t)  YAML_TEMPLATE=$OPTARG
    k)  KUBECONFIG=$OPTARG
# Set kubeconfig flag if config specified
if [[ ! -z $KUBECONFIG ]]; then
  if [[ -f $KUBECONFIG ]]; then
    KUBECONFIG="--kubeconfig $KUBECONFIG"
    KUBECONFIG=""
# Conditional Defaults
if [[ -z $REVERSE_CIDRS ]]; then
  REVERSE_CIDRS="in-addr.arpa ip6.arpa"
if [[ -z $CLUSTER_DNS_IP ]]; then
  # Default IP to kube-dns IP
  CLUSTER_DNS_IP=$(kubectl get service --namespace kube-system kube-dns -o jsonpath="{.spec.clusterIP}" $KUBECONFIG)
  if [ $? -ne 0 ]; then
      >&2 echo "Error! The IP address for DNS service couldn't be determined automatically. Please specify the DNS-IP with the '-i' option."
      exit 2
if [[ "${SKIP}" -ne 1 ]] ; then
    translate-kube-dns-configmap
orig=$'\n'
replace=$'\\\n'
sed -e "s/CLUSTER_DNS_IP/$CLUSTER_DNS_IP/g" \
    -e "s/CLUSTER_DOMAIN/$CLUSTER_DOMAIN/g" \
    -e "s?REVERSE_CIDRS?$REVERSE_CIDRS?g" \
    -e "s@STUBDOMAINS@${STUBDOMAINS//$orig/$replace}@g" \
    -e "s@FEDERATIONS@${FEDERATIONS//$orig/$replace}@g" \
    -e "s/UPSTREAMNAMESERVER/$UPSTREAM/g" \
    "${YAML_TEMPLATE}"

6.配置文件并部署服务


首先第一步要知道集群使用的DNS的IP地址

-e s/CLUSTER_DNS_IP/$CLUSTER_DNS_IP/g 
-e s/CLUSTER_DOMAIN/$CLUSTER_DOMAIN/g 
-e "s?REVERSE_CIDRS?$REVERSE_CIDRS?g" 
$YAML_TEMPLATE
其中REVERSE_CIDRS就是上游的IP地址。
in-addr.arpa ip6.arpa

查看配置在模板yaml文件的位置

REVERSE_CIDRS="10.0.6.0/24" ## 配置 kubernetes svc 网段
CLUSTER_DNS_IP="10.0.6.200" ## 配置 kubernetes DNS IP
CLUSTER_DOMAIN="cluster.local" ## 配置 kubernetes 的域名
YAML_TEMPLATE=$basedir/coredns.yaml.sed ## coredns 的模板yaml文件
## function
function create_coredns_yaml(){
local TEMPLATE=$basedir/coredns.yaml.simple
local YAML=$basedir/coredns.yaml
cat $YAML_TEMPLATE > $TEMPLATE
sed -e s/CLUSTER_DNS_IP/$CLUSTER_DNS_IP/g -e s/CLUSTER_DOMAIN/$CLUSTER_DOMAIN/g -e "s?REVERSE_CIDRS?$REVERSE_CIDRS?g"  $TEMPLATE > $YAML
create_coredns_yaml

执行配置脚本，生成部署coreDNS.yaml文件


留下一个问题


在经过上面的一系列部署之后，kuberntes的虚拟集群网络的DNS解析的确是可以的了。但是kubernetes之外的物理机node也是需要DNS解析的，那么该怎么去管理呢？

下面后续一个篇章，我会介绍使用dnsmasq的部署，方便管理kuberntes集群以及多台物理机服务器的DNS统一管理。
 
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