本文将在前文的基础上介绍在kubernetes集群环境中配置dns服务，在k8s集群中，pod的生命周期是短暂的，pod重启后ip地址会产生变化，对于应用程序来说这是不可接受的，为解决这个问题，K8S集群巧妙的引入的dns服务来实现服务的发现，在k8s集群中dns总共需要使用4个组件，各组件分工如下：
etcd：DNS存储
kube2sky：将Kubernetes Master中的service（服务）注册到etcd。
skyDNS：提供DNS域名解析服务。
healthz：提供对skydns服务的健康检查。

一、下载相关镜像文件，并纳入本地仓库统一管理

# docker pull docker.io/elcolio/etcd
# docker pull docker.io/port/kubernetes-kube2sky
# docker pull docker.io/skynetservices/skydns
# docker pull docker.io/wu1boy/healthz# docker tag docker.io/elcolio/etcd registry.fjhb.cn/etcd
# docker tag docker.io/port/kubernetes-kube2sky registry.fjhb.cn/kubernetes-kube2sky
# docker tag docker.io/skynetservices/skydns  registry.fjhb.cn/skydns
# docker tag docker.io/wu1boy/healthz registry.fjhb.cn/healthz# docker push registry.fjhb.cn/etcd
# docker push registry.fjhb.cn/kubernetes-kube2sky
# docker push registry.fjhb.cn/skydns
# docker push registry.fjhb.cn/healthz
# docker images |grep fjhb

二、通过rc文件创建pod
这里面一个pod包含了4个组件，一个组件运行在一个docker容器中

# cat skydns-rc.yaml
apiVersion: v1
kind: ReplicationController
metadata:name: kube-dnsnamespace: defaultlabels:k8s-app: kube-dnsversion: v12kubernetes.io/cluster-service: "true"
spec:replicas: 1selector:k8s-app: kube-dnsversion: v12template:metadata:labels:k8s-app: kube-dnsversion: v12kubernetes.io/cluster-service: "true"spec:containers:- name: etcdimage: registry.fjhb.cn/etcd resources:limits:cpu: 100mmemory: 50Mirequests:cpu: 100mmemory: 50Micommand:- /bin/etcd- --data-dir- /tmp/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-etcdvolumeMounts:- name: etcd-storagemountPath: /tmp/data- name: kube2skyimage: registry.fjhb.cn/kubernetes-kube2skyresources:limits:cpu: 100mmemory: 50Mirequests:cpu: 100mmemory: 50Miargs:- -kube_master_url=http://192.168.115.5:8080- -domain=cluster.local- name: skydnsimage: registry.fjhb.cn/skydns resources:limits:cpu: 100mmemory: 50Mirequests:cpu: 100mmemory: 50Miargs:- -machines=http://127.0.0.1:4001- -addr=0.0.0.0:53- -ns-rotate=false- -domain=cluster.localports:- containerPort: 53name: dnsprotocol: UDP- containerPort: 53name: dns-tcpprotocol: TCP- name: healthzimage: registry.fjhb.cn/healthzresources:limits:cpu: 10mmemory: 20Mirequests:cpu: 10mmemory: 20Miargs:- -cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1 >/dev/null- -port=8080ports:- containerPort: 8080protocol: TCPvolumes:- name: etcd-storageemptyDir: {}dnsPolicy: Default

三、通过srv文件创建service

# cat skydns-svc.yaml
apiVersion: v1
kind: Service
metadata:name: kube-dnsnamespace: defaultlabels:k8s-app: kube-dnskubernetes.io/cluster-service: "true"kubernetes.io/name: "KubeDNS"
spec:selector:k8s-app: kube-dnsclusterIP: 10.254.16.254ports:- name: dnsport: 53protocol: UDP- name: dns-tcpport: 53protocol: TCP

# kubectl create -f skydns-rc.yaml
# kubectl create -f skydns-svc.yaml
# kubectl get rc
# kubectl get pod
# kubectl get svc

# kubectl describe svc kube-dns

# kubectl describe rc kube-dns

# kubectl describe pod kube-dns-9fllp
Name:           kube-dns-9fllp
Namespace:      default
Node:           192.168.115.6/192.168.115.6
Start Time:     Tue, 23 Jan 2018 10:55:19 -0500
Labels:         k8s-app=kube-dnskubernetes.io/cluster-service=trueversion=v12
Status:         Running
IP:             172.16.37.5
Controllers:    ReplicationController/kube-dns
Containers:etcd:Container ID:       docker://62ad76bfaca1797c5f43b0e9eebc04074169fce4cc15ef3ffc4cd19ffa9c8c19Image:              registry.fjhb.cn/etcdImage ID:           docker-pullable://docker.io/elcolio/etcd@sha256:3b4dcd35a7eefea9ce2970c81dcdf0d0801a778d117735ee1d883222de8bbd9fPort:Command:/bin/etcd--data-dir/tmp/data--listen-client-urlshttp://127.0.0.1:2379,http://127.0.0.1:4001--advertise-client-urlshttp://127.0.0.1:2379,http://127.0.0.1:4001--initial-cluster-tokenskydns-etcdLimits:cpu:      100mmemory:   50MiRequests:cpu:              100mmemory:           50MiState:              RunningStarted:          Tue, 23 Jan 2018 10:55:23 -0500Ready:              TrueRestart Count:      0Volume Mounts:/tmp/data from etcd-storage (rw)/var/run/secrets/kubernetes.io/serviceaccount from default-token-6pddn (ro)Environment Variables:      <none>kube2sky:Container ID:       docker://6b0bc6e8dce83e3eee5c7e654fbaca693730623fb7936a1fd9d73de1a1dd8152Image:              registry.fjhb.cn/kubernetes-kube2skyImage ID:           docker-pullable://docker.io/port/kubernetes-kube2sky@sha256:0230d3fbb0aeb4ddcf903811441cf2911769dbe317a55187f58ca84c95107ff5Port:Args:-kube_master_url=http://192.168.115.5:8080-domain=cluster.localLimits:cpu:      100mmemory:   50MiRequests:cpu:              100mmemory:           50MiState:              RunningStarted:          Tue, 23 Jan 2018 10:55:25 -0500Ready:              TrueRestart Count:      0Volume Mounts:/var/run/secrets/kubernetes.io/serviceaccount from default-token-6pddn (ro)Environment Variables:      <none>skydns:Container ID:       docker://ebc2aaaa54e2f922e370e454ec537665d813c69d37a21e3afd908e6dad056627Image:              registry.fjhb.cn/skydnsImage ID:           docker-pullable://docker.io/skynetservices/skydns@sha256:6f8a9cff0b946574bb59804016d3aacebc637581bace452db6a7515fa2df79eePorts:              53/UDP, 53/TCPArgs:-machines=http://127.0.0.1:4001-addr=0.0.0.0:53-ns-rotate=false-domain=cluster.localLimits:cpu:      100mmemory:   50MiRequests:cpu:              100mmemory:           50MiState:              RunningStarted:          Tue, 23 Jan 2018 10:55:27 -0500Ready:              TrueRestart Count:      0Volume Mounts:/var/run/secrets/kubernetes.io/serviceaccount from default-token-6pddn (ro)Environment Variables:      <none>healthz:Container ID:       docker://f1de1189fa6b51281d414d7a739b86494b04c8271dc6bb5f20c51fac15ec9601Image:              registry.fjhb.cn/healthzImage ID:           docker-pullable://docker.io/wu1boy/healthz@sha256:d6690c0a8cc4f810a5e691b6a9b8b035192cb967cb10e91c74824bb4c8eea796Port:               8080/TCPArgs:-cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1 >/dev/null-port=8080Limits:cpu:      10mmemory:   20MiRequests:cpu:              10mmemory:           20MiState:              RunningStarted:          Tue, 23 Jan 2018 10:55:29 -0500Ready:              TrueRestart Count:      0Volume Mounts:/var/run/secrets/kubernetes.io/serviceaccount from default-token-6pddn (ro)Environment Variables:      <none>
Conditions:Type          StatusInitialized   True Ready         True PodScheduled  True
Volumes:etcd-storage:Type:       EmptyDir (a temporary directory that shares a pod's lifetime)Medium:default-token-6pddn:Type:       Secret (a volume populated by a Secret)SecretName: default-token-6pddn
QoS Class:      Guaranteed
Tolerations:    <none>
Events:FirstSeen     LastSeen        Count   From                    SubObjectPath                   Type            Reason        Message---------     --------        -----   ----                    -------------                   --------        ------        -------7m            7m              1       {default-scheduler }                                    Normal          Scheduled     Successfully assigned kube-dns-9fllp to 192.168.115.67m            7m              1       {kubelet 192.168.115.6} spec.containers{etcd}           Normal          Pulling       pulling image "registry.fjhb.cn/etcd"7m            7m              1       {kubelet 192.168.115.6} spec.containers{etcd}           Normal          Pulled        Successfully pulled image "registry.fjhb.cn/etcd"7m            7m              1       {kubelet 192.168.115.6} spec.containers{etcd}           Normal          Created       Created container with docker id 62ad76bfaca1; Security:[seccomp=unconfined]7m            7m              1       {kubelet 192.168.115.6} spec.containers{kube2sky}       Normal          Pulled        Successfully pulled image "registry.fjhb.cn/kubernetes-kube2sky"7m            7m              1       {kubelet 192.168.115.6} spec.containers{etcd}           Normal          Started       Started container with docker id 62ad76bfaca17m            7m              1       {kubelet 192.168.115.6} spec.containers{kube2sky}       Normal          Pulling       pulling image "registry.fjhb.cn/kubernetes-kube2sky"7m            7m              1       {kubelet 192.168.115.6} spec.containers{kube2sky}       Normal          Created       Created container with docker id 6b0bc6e8dce8; Security:[seccomp=unconfined]7m            7m              1       {kubelet 192.168.115.6} spec.containers{skydns}         Normal          Pulled        Successfully pulled image "registry.fjhb.cn/skydns"7m            7m              1       {kubelet 192.168.115.6} spec.containers{skydns}         Normal          Pulling       pulling image "registry.fjhb.cn/skydns"7m            7m              1       {kubelet 192.168.115.6} spec.containers{kube2sky}       Normal          Started       Started container with docker id 6b0bc6e8dce87m            7m              1       {kubelet 192.168.115.6} spec.containers{skydns}         Normal          Created       Created container with docker id ebc2aaaa54e2; Security:[seccomp=unconfined]7m            7m              1       {kubelet 192.168.115.6} spec.containers{skydns}         Normal          Started       Started container with docker id ebc2aaaa54e27m            7m              1       {kubelet 192.168.115.6} spec.containers{healthz}        Normal          Pulling       pulling image "registry.fjhb.cn/healthz"7m            7m              1       {kubelet 192.168.115.6} spec.containers{healthz}        Normal          Pulled        Successfully pulled image "registry.fjhb.cn/healthz"7m            7m              1       {kubelet 192.168.115.6} spec.containers{healthz}        Normal          Created       Created container with docker id f1de1189fa6b; Security:[seccomp=unconfined]7m            7m              1       {kubelet 192.168.115.6} spec.containers{healthz}        Normal          Started       Started container with docker id f1de1189fa6b

四、修改kubelet配置文件并重启服务
注意:
--cluster-dns参数要和前面svc文件中的clusterIP参数一致
--cluster-domain参数要和前面rc文件中的-domain参数一致
集群内所有的kubelet节点都需要修改

# grep 'KUBELET_ADDRESS' /etc/kubernetes/kubelet
KUBELET_ADDRESS="--address=192.168.115.5 --cluster-dns=10.254.16.254 --cluster-domain=cluster.local"
# systemctl restart kubelet

五、运行一个busybox和curl进行测试

# cat busybox.yaml
apiVersion: v1
kind: Pod
metadata:name: busybox
spec:containers:- name: busyboximage: docker.io/busyboxcommand:- sleep
- "3600"

# cat curl.yaml
apiVersion: v1
kind: Pod
metadata:name: curl
spec:containers:- name: curlimage: docker.io/webwurst/curl-utilscommand:- sleep
- "3600"

# kubectl create -f busybox.yaml
# kubectl create -f curl.yaml

通过busybox容器对kubernetes的service进行解析，发现service被自动解析成了对应的集群ip地址，而并不是172.16网段的docker地址

# kubectl get svc
# kubectl exec busybox -- nslookup frontend
# kubectl exec busybox -- nslookup redis-master
# kubectl exec busybox -- nslookup redis-slave

通过curl容器访问前面创建的php留言板

# kubectl exec curl -- curl frontend