Kubernetes采用CoreDNS

企业开发 2018-11-09 15:14:02 阅读次数: 0

参考文档：

  1. kubernetes插件：https://github.com/kubernetes/kubernetes/tree/master/cluster/addons/dns/coredns
  2. 自定义dns服务：https://kubernetes.io/docs/tasks/administer-cluster/dns-custom-nameservers/
  3. CoreDNS提供直接替换kube-dns的部署方式，请见：https://github.com/coredns/deployment/tree/master/kubernetes

从功能角度来看，CoreDNS 更像是一个通用 DNS 方案（类似于 BIND），然后通过插件模式来极大地扩展自身功能，可以适用于不同的场景（比如 Kubernetes）。

一．环境

kubernetes集群已提前部署完成：https://www.cnblogs.com/netonline/tag/kubernetes/

组件版本如下：

组件

版本

Remark

kubernetes

v1.9.2

  

CoreDNS

v1.2.2

  

 

二．部署CoreDNS

1. coredns范本

# 下载

[root@kubenode1 coredns]# cd ~

[root@kubenode1 ~]# mkdir -p /usr/local/src/yaml/coredns

[root@kubenode1 ~]# cd /usr/local/src/yaml/coredns

[root@kubenode1 coredns]# wget -O coredns.yaml https://raw.githubusercontent.com/kubernetes/kubernetes/master/cluster/addons/dns/coredns/coredns.yaml.base

# 本实验使用yaml文件（修改版，供参考）：https://github.com/Netonline2016/kubernetes/tree/master/addons/coredns

2. 配置coredns.yaml

# coredns所有相关资源通过1个yaml文件下发，注意红色加粗字体部分即需要根据规划修改；

# 将"ConfigMap"资源抽出来单独做1个yaml文件，方便后续修改上游dns服务器或自定义dns记录；

# 除"ConfigMap"资源抽出外，主要修改两处："Deployment"资源的"image"与"Service"中的"clusterip"；

# 在deployment中设置pod的副本数为2（可选）

[root@kubenode1 coredns]# vim coredns.yaml

# Warning: This is a file generated from the base underscore template file: coredns.yaml.base

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

---

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: extensions/v1beta1

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:

# 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.

replicas: 2

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:

serviceAccountName: coredns

tolerations:

- key: node-role.kubernetes.io/master

effect: NoSchedule

- key: "CriticalAddonsOnly"

operator: "Exists"

containers:

- name: coredns

image: netonline/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

livenessProbe:

httpGet:

path: /health

port: 8080

scheme: HTTP

initialDelaySeconds: 60

timeoutSeconds: 5

successThreshold: 1

failureThreshold: 5

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: "9153"

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

clusterIP: 169.169.0.11

ports:

- name: dns

port: 53

protocol: UDP

- name: dns-tcp

port: 53

protocol: TCP

3. 配置coredns-cm.yaml

# 单列ConfigMap资源，方便后续设置上游dns服务器与自定义dns记录；

# coredns通过corefie控制dns记录，kubernetes中采用ConfigMap将corefile文件映射到pod中，可以发现coredns "Deployment"资源中挂载了相应的"ConfigMap"，必须设置；

# corefile格式如下：

# ZONE:[PORT] {

# [PLUGIN] ...

# }

# ZONE：定义 server 负责的 zone，PORT 是可选项，默认为 53；

# PLUGIN：定义 server 所要加载的 plugin，如errors，health等均属于plugin，相关注解请见：https://kubernetes.io/docs/tasks/administer-cluster/dns-custom-nameservers/#coredns；

[root@kubenode1 coredns]# cat coredns-cm.yaml

apiVersion: v1

kind: ConfigMap

metadata:

name: coredns

namespace: kube-system

labels:

addonmanager.kubernetes.io/mode: EnsureExists

data:

Corefile: |

.:53 {

errors

health

kubernetes cluster.local in-addr.arpa ip6.arpa {

pods insecure

# 用于解析外部主机主机（外部服务）

upstream 114.114.114.114 223.5.5.5

fallthrough in-addr.arpa ip6.arpa

}

prometheus :9153

# 任何不在集群域内的查询将转发到预定义的解析器，默认：/etc/resolv.conf；

# 在coredns "Deployment"资源中"dnsPolicy"设置为"Default"，即提供dns服务的pod从所在节点继承/etc/resolv.conf，如果节点的上游解析地址与"upstream"一致，则设置任意一个参数即可

proxy . 114.114.114.114 223.5.5.5

cache 30

loop

reload

loadbalance

}

# 自定义dns记录，对应kube-dns中的stubdomains；

# 每条记录，单独设置1各zone

out.kubernetes:53 {

errors

cache 30

proxy . 172.30.200.15

}

4. 启动coredns

# 删除kube-dns相关资源

[root@kubenode1 coredns]# kubectl delete -f /usr/local/src/yaml/kubedns/kube-dns.yaml

# 启动coredns；

# coredns pod需要挂载"ConfigMap"资源，需要同时或提前下发相关资源

[root@kubenode1 coredns]# kubectl create -f coredns-cm.yaml

configmap "coredns" created

[root@kubenode1 coredns]# kubectl create -f coredns.yaml

 

三．验证

1. 自定义dns服务器

# "ConfigMap" 中自定义的dns记录指向172.30.200.15，在其上安装dnsmasq服务

[root@salt-master01 ~]# yum install dnsmasq -y

# 生成自定义的DNS记录文件

[root@salt-master01 ~]# echo "192.168.100.11 server.out.kubernetes" > /tmp/hosts

# 启动DNS服务；

# -q：输出查询记录；

# -d：以debug模式启动，前台运行，观察输出日志；

# -h：不使用/etc/hosts；

# -R：不使用/etc/resolv.conf；

# -H：使用自定义的DNS记录文件；

# 启动输出日志中warning提示没有设置上游DNS服务器；同时读入自定义DNS记录文件

[root@salt-master01 ~]# dnsmasq -q -d -h -R -H /tmp/hosts

# iptables放行udp 53端口

[root@salt-master01 ~]# iptables -I INPUT -m state --state NEW -m udp -p udp --dport 53 -j ACCEPT

2. 启动验证Pod

# 下载镜像

[root@kubenode1 ~]# docker pull busybox

# 配置Pod yaml文件；

# dnsPolicy设置为ClusterFirst，默认也是ClusterFirst

[root@kubenode1 ~]# touch dnstest.yaml

[root@kubenode1 ~]# vim dnstest.yaml

apiVersion: v1

kind: Pod

metadata:

name: dnstest

namespace: default

spec:

dnsPolicy: ClusterFirst

containers:

- name: busybox

image: busybox

command:

- sleep

- "3600"

imagePullPolicy: IfNotPresent

restartPolicy: Always

# 创建Pod

[root@kubenode1 ~]# kubectl create -f dnstest.yaml

3. 验证

# 分别针对3各域名进行nslookup查询

[root@kubenode1 ~]# kubectl exec -it dnstest -- nslookup kubernetes.default

[root@kubenode1 ~]# kubectl exec -it dnstest -- nslookup www.baidu.com

[root@kubenode1 ~]# kubectl exec -it dnstest -- nslookup server.out.kubernetes

观察172.30.200.15上dnsmasq服务的输出：kube节点172.30.200.22与172.30.200.23（Pod所在的节点，flannel网络，snat出节点）对server.out.kubenetes的查询，dnsmasq返回预定义的主机地址。

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