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。
1.修改所有node的配置文件：/etc/kubernetes/kubelet kubernetes-node1，kubernetes-node2，kubernetes-node3:
[root@kubernetes-node2 ~]# tail -n 1 /etc/kubernetes/kubelet
KUBELET_ARGS="--cluster-dns=10.254.254.254 --cluster-domain=cluster.local"
2.所有node节点都重新启动服务
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。
[root@kubernetes-master pods]# cat kube-system.yml
apiVersion: v1
kind: Namespace
metadata:
name: kube-system
4.在master服务器上编辑ReplicationController文件dns-rc.yml
1 apiVersion: v1
2 kind: ReplicationController
3 metadata:
4 name: kube-dns-v11
5 namespace: kube-system
6 labels:
7 k8s-app: kube-dns
8 version: v11
9 kubernetes.io/cluster-service: "true"
10 spec:
11 replicas: 1
12 selector:
13 k8s-app: kube-dns
14 version: v11
15 template:
16 metadata:
17 labels:
18 k8s-app: kube-dns
19 version: v11
20 kubernetes.io/cluster-service: "true"
21 spec:
22 containers:
23 - name: etcd
24 image: docker.gaoxiaobang.com/kubernetes/etcd-amd64:2.2.1
25 resources:
26 limits:
27 cpu: 100m
28 memory: 500Mi
29 requests:
30 cpu: 100m
31 memory: 50Mi
32 command:
33 - /usr/local/bin/etcd
34 - -data-dir
35 - /var/etcd/data
36 - -listen-client-urls
37 - http://127.0.0.1:2379,http://127.0.0.1:4001
38 - -advertise-client-urls
39 - http://127.0.0.1:2379,http://127.0.0.1:4001
40 - -initial-cluster-token
41 - skydns-etcd
42 #volumeMounts:
43 #- name: etcd-storage
44 # mountPath: /var/etcd/data
45 - name: kube2sky
46 image: docker.gaoxiaobang.com/kubernetes/kube2sky:1.14
47 args:
48 # command = "/kube2sky"
49 - --domain=cluster.local
50 - --kube-master-url=http://10.64.8.68:8080
51 resources:
52 limits:
53 cpu: 100m
54 memory: 200Mi
55 requests:
56 cpu: 100m
57 memory: 50Mi
58 - name: skydns
59 image: docker.gaoxiaobang.com/kubernetes/skydns:2015-10-13-8c72f8c
60 resources:
61 limits:
62 cpu: 100m
63 memory: 200Mi
64 requests:
65 cpu: 100m
66 memory: 50Mi
67 args:
68 - -machines=http://127.0.0.1:4001
69 - -addr=0.0.0.0:53
70 - -ns-rotate=false
71 - -domain=cluster.local.
72 ports:
73 - containerPort: 53
74 name: dns
75 protocol: UDP
76 - containerPort: 53
77 name: dns-tcp
78 protocol: TCP
79 livenessProbe:
80 httpGet:
81 path: /healthz
82 port: 8080
83 scheme: HTTP
84 initialDelaySeconds: 60
85 timeoutSeconds: 5
86 successThreshold: 1
87 failureThreshold: 5
88 readinessProbe:
89 httpGet:
90 path: /readiness
91 port: 8080
92 scheme: HTTP
93 initialDelaySeconds: 30
94 timeoutSeconds: 5
95 - name: healthz
96 image: docker.gaoxiaobang.com/kubernetes/exechealthz:1.0
97 resources:
98 limits:
99 cpu: 10m
100 memory: 20Mi
101 requests:
102 cpu: 10m
103 memory: 20Mi
104 args:
105 - -cmd=nslookup kubernetes.default.svc.cluster.local localhost >/dev/null
106 - -port=8080
107 ports:
108 - containerPort: 8080
109 protocol: TCP
110 volumes:
111 - name: etcd-storage
112 emptyDir: {}
113 dnsPolicy: Default dns-rc.yml
注意dns-rc.yml：修改文件中的master ip
dns service服务yml
1 apiVersion: v1
2 kind: Service
3 metadata:
4 name: kube-dns
5 namespace: kube-system
6 labels:
7 k8s-app: kube-dns
8 kubernetes.io/cluster-service: "true"
9 kubernetes.io/name: "KubeDNS"
10 spec:
11 selector:
12 k8s-app: kube-dns
13 clusterIP: 10.254.254.254
14 ports:
15 - name: dns
16 port: 53
17 protocol: UDP
18 - name: dns-tcp
19 port: 53
20 protocol: TCP dns-svc.yml
创建namespace（有就不用在创建了）
kubectl create -f kube-system.yml
创建ReplicationController
[root@kubernetes-master pods]# kubectl create -f dns-rc.yml
创建Service
[root@kubernetes-master pods]# kubectl create -f dns-svc.yml
查看dns-rc.yml文件中定义pod的启动状态，如下则启动成功。
[root@kubernetes-master pods]# kubectl get pod --namespace=kube-system
查看dns-svc.yml文件中定义的Service的信息。
[root@kubernetes-master pods]# kubectl get svc -l k8s-app=kube-dns --namespace=kube-system
测试DNS的效果。
部署一个busybox的Pod
1 apiVersion: v1
2 kind: Pod
3 metadata:
4 name: busybox
5 namespace: default
6 spec:
7 containers:
8 - image: busybox
9 command:
10 - sleep
11 - "3600"
12 imagePullPolicy: IfNotPresent
13 name: busybox
14 restartPolicy: Always busybox.yml
验证kubernetes服务的地址解析，出现如下所示则证明DNS解析正常。