k8s入门系列之扩展组件(一)DNS安装篇

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: 1
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-amd64:2.2.1
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:2015-10-13-8c72f8c
resources:
limits:
cpu: 100m
memory: 200Mi
requests:
cpu: 100m
memory: 50Mi
args:
- -machines=http://127.0.0.1:4001
- -addr=0.0.0.0:53
- -ns-rotate=false
- -domain=cluster.local.
ports:
- containerPort: 53
name: dns
protocol: UDP
- containerPort: 53
name: dns-tcp
protocol: TCP
livenessProbe:
httpGet:
path: /healthz
port: 8080
scheme: HTTP
initialDelaySeconds: 60
timeoutSeconds: 5
successThreshold: 1
failureThreshold: 5
readinessProbe:
httpGet:
path: /readiness
port: 8080
scheme: HTTP
initialDelaySeconds: 30
timeoutSeconds: 5
- 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=8080
ports:
- containerPort: 8080
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: 53
protocol: UDP
- name: dns-tcp
port: 53
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           4/4       Running   8          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>        53/UDP,53/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
- "3600"
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 1: 10.254.254.254

Name:      kubernetes
Address 1: 10.254.0.1

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