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:
# 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
# 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。
# 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
# 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
# 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
# kubectl create -f kube-system.yml
·创建ReplicationController
# kubectl create -f skydns-rc.yml
·创建Service
# 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。
# 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。
# 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
# 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。
# 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。
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