DNS (domain name system),提供域名解析服务,解决了难于记忆的IP地址问题,以更人性可读可记忆可标识的方式映射对应IP地址。

Cluster DNS扩展插件用于支持k8s集群系统中各服务之间发现与调用。

  

组件:
  •SkyDNS 提供DNS解析服务
  •Etcd 存储DNS信息
  •Kube2sky 监听kubernetes,当有Service创建时,生成相应的记录到SkyDNS。

本文章的实验环境与《k8s入门系列之集群安装篇》介绍中一致。master(1) + node(4)
1.修改所有node的配置文件:/etc/kubernetes/kubelet
node1,node2,node3.node4:

[root@node1 ~]# tail -n 1 /etc/kubernetes/kubelet

KUBELET_ARGS="--cluster-dns=10.254.254.254 --cluster-domain=cluster.local"

2.所有node(node1,node2,node3,node4)重新启动kubelet服务

[root@node1 ~]# systemctl restart kubelet.service

3.根据namespace分为不同的名称空间,将系统服务统一放到一个单独的空间:kube-system,由于默认空间只有default,我们首先要创建kube-system空间。

[root@master skydns]# cat kube-system.yml

apiVersion: v1
kind: Namespace
metadata:
name: kube-system

4.在master服务器上编辑ReplicationController文件skydns-rc.yml

[root@master skydns]# cat skydns-rc.yml

apiVersion: v1
kind: ReplicationController
metadata:
name: kube-dns-v11
namespace: kube-system
labels:
k8s-app: kube-dns
version: v11
kubernetes.io/cluster-service: "true"
spec:
replicas:
selector:
k8s-app: kube-dns
version: v11
template:
metadata:
labels:
k8s-app: kube-dns
version: v11
kubernetes.io/cluster-service: "true"
spec:
containers:
- name: etcd
image: docker.gaoxiaobang.com/kubernetes/etcd-amd64:2.2.
resources:
limits:
cpu: 100m
memory: 500Mi
requests:
cpu: 100m
memory: 50Mi
command:
- /usr/local/bin/etcd
- -data-dir
- /var/etcd/data
- -listen-client-urls
- http://127.0.0.1:2379,http://127.0.0.1:4001
- -advertise-client-urls
- http://127.0.0.1:2379,http://127.0.0.1:4001
- -initial-cluster-token
- skydns-etcd
#volumeMounts:
#- name: etcd-storage
# mountPath: /var/etcd/data
- name: kube2sky
image: docker.gaoxiaobang.com/kubernetes/kube2sky:1.14
args:
# command = "/kube2sky"
- --domain=cluster.local
- --kube-master-url=http://192.168.30.20:8080
resources:
limits:
cpu: 100m
memory: 200Mi
requests:
cpu: 100m
memory: 50Mi
- name: skydns
image: docker.gaoxiaobang.com/kubernetes/skydns:---8c72f8c
resources:
limits:
cpu: 100m
memory: 200Mi
requests:
cpu: 100m
memory: 50Mi
args:
- -machines=http://127.0.0.1:4001
- -addr=0.0.0.0:
- -ns-rotate=false
- -domain=cluster.local.
ports:
- containerPort:
name: dns
protocol: UDP
- containerPort:
name: dns-tcp
protocol: TCP
livenessProbe:
httpGet:
path: /healthz
port:
scheme: HTTP
initialDelaySeconds:
timeoutSeconds:
successThreshold:
failureThreshold:
readinessProbe:
httpGet:
path: /readiness
port:
scheme: HTTP
initialDelaySeconds:
timeoutSeconds:
- name: healthz
image: docker.gaoxiaobang.com/kubernetes/exechealthz:1.0
resources:
limits:
cpu: 10m
memory: 20Mi
requests:
cpu: 10m
memory: 20Mi
args:
- -cmd=nslookup kubernetes.default.svc.cluster.local localhost >/dev/null
- -port=
ports:
- containerPort:
protocol: TCP
volumes:
- name: etcd-storage
emptyDir: {}
dnsPolicy: Default

5.在master上创建skydns服务文件skydns-svc.yml
[root@master skydns]# cat skydns-svc.yml

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
clusterIP: 10.254.254.254
ports:
- name: dns
port:
protocol: UDP
- name: dns-tcp
port:
protocol: TCP

6.在集群中创建cluster-dns解析应用

•创建Namespace

[root@master skydns]# kubectl create -f kube-system.yml

•创建ReplicationController

[root@master skydns]# kubectl create -f skydns-rc.yml

•创建Service

[root@master skydns]# kubectl create -f skydns-svc.yml

7.查看skydns-rc.yml文件中定义pod的启动状态,如下则启动成功。

[root@master skydns]# kubectl get pod --namespace=kube-system
NAME READY STATUS RESTARTS AGE
kube-dns-v11-ey14j / Running 1d

8.查看skydns-svc.yml文件中定义的Service的信息。

[root@master skydns]# kubectl get svc -l k8s-app=kube-dns --namespace=kube-system
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kube-dns 10.254.254.254 <none> /UDP,/TCP 1d

9.测试DNS的效果。
•部署一个busybox的Pod
[root@master test]# cat busybox.yml

apiVersion: v1
kind: Pod
metadata:
name: busybox
namespace: default
spec:
containers:
- image: busybox
command:
- sleep
- ""
imagePullPolicy: IfNotPresent
name: busybox
restartPolicy: Always

•验证kubernetes服务的地址解析,出现如下所示则证明DNS解析正常。

[root@master test]# kubectl exec busybox nslookup kubernetes
Server: 10.254.254.254
Address : 10.254.254.254 Name: kubernetes
Address : 10.254.0.1

*提示:kubernetes服务是kubernetes集群安装之后默认的一个服务。

05-02 21:56