摘要：
本文主要介绍Kubernetes 1.4中DNS插件的安装。1.4中的DNS添加了一个新功能来解析与Pod（HostName）对应的域名。DNS组件由kubedns（监控Kubernetes中的服务更改）、dnsmasq（DNS服务）和健康检查容器healthz组成。
目录贴：Kubernetes学习系列
1、介绍
之前介绍过DNS的搭建（基于Kubernetes集群部署skyDNS服务），但那个版本的DNS是随着Kubernetes1.2发布出来的，有点原始。本文主要讲解Kubernetes1.4版本中的DNS插件的安装。与1.2版本相比，1.4中的DNS增加了解析Pod（HostName）对应的域名的新功能，且在部署上也有了一些变化。1.2中，需要部署etcd（或使用master上的Etcd）、kube2sky、skydns三个组件；1.4中，DNS组件由kubedns（监控Kubernetes中service变化）、dnsmasq（DNS服务）和一个健康检查容器——healthz组成。
在搭建PetSet（宠物应用）时，系统首先要为PetSet设置一个HeadLess service，即service的ClusterIP显示的设置成none，而对每一个有特定名称的Pet（Named Pod），可以通过其HostName进行寻址访问。这就用到了1.4中的新功能。以下给出具体的搭建过程。
2、修改配置
2.1修改各个node上的kubelet
修改以下红色部分，完成后重启kubelet服务。
[root@k8s-node-1 ~]# cat /etc/kubernetes/kubelet ### # kubernetes kubelet (minion) config # The address for the info server to serve on (set to 0.0.0.0 or "" for all interfaces) KUBELET_ADDRESS="--address=0.0.0.0" # The port for the info server to serve on # KUBELET_PORT="--port=10250" # You may leave this blank to use the actual hostname #KUBELET_HOSTNAME="--hostname-override=127.0.0.1" KUBELET_HOSTNAME="--hostname-override=k8s-node-1" # location of the api-server KUBELET_API_SERVER="--api-servers=http://k8s-master:8080" # pod infrastructure container KUBELET_POD_INFRA_CONTAINER="--pod-infra-container-image=registry.access.redhat.com/rhel7/pod-infrastructure:latest" # Add your own! #KUBELET_ARGS="" KUBELET_ARGS="--cluster-dns=10.254.10.2 --cluster-domain=cluster.local. --allow-privileged=true" [root@k8s-node-1 ~]# systemctl restart kubelet.service
2.2修改APIserver
修改以下红色部分：
[root@k8s-master ~]# cat /etc/kubernetes/apiserver ### # kubernetes system config # # The following values are used to configure the kube-apiserver # # The address on the local server to listen to. KUBE_API_ADDRESS="--insecure-bind-address=0.0.0.0" # The port on the local server to listen on. KUBE_API_PORT="--port=8080" # Port minions listen on # KUBELET_PORT="--kubelet-port=10250" # Comma separated list of nodes in the etcd cluster KUBE_ETCD_SERVERS="--etcd-servers=http://etcd:2379" # Address range to use for services KUBE_SERVICE_ADDRESSES="--service-cluster-ip-range=10.254.0.0/16" # default admission control policies KUBE_ADMISSION_CONTROL="--admission-control=NamespaceLifecycle,NamespaceExists,LimitRanger,SecurityContextDeny,ResourceQuota" # Add your own! KUBE_API_ARGS=""
2.3 修改yaml文件
修改以下红色部分：
[root@k8s-master dns14]# cat kube-dns-rc_14.yaml apiVersion: v1 kind: ReplicationController metadata: name: kube-dns-v20 namespace: kube-system labels: k8s-app: kube-dns version: v20 kubernetes.io/cluster-service: "true" spec: replicas: 1 selector: k8s-app: kube-dns version: v20 template: metadata: labels: k8s-app: kube-dns version: v20 annotations: scheduler.alpha.kubernetes.io/critical-pod: '' scheduler.alpha.kubernetes.io/tolerations: '[{"key":"CriticalAddonsOnly", "operator":"Exists"}]' spec: containers: - name: kubedns image: gcr.io/google_containers/kubedns-amd64:1.8 imagePullPolicy: IfNotPresent resources: # TODO: Set memory limits when we've profiled the container for large # clusters, then set request = limit to keep this container in # guaranteed class. Currently, this container falls into the # "burstable" category so the kubelet doesn't backoff from restarting it. limits: memory: 170Mi requests: cpu: 100m memory: 70Mi livenessProbe: httpGet: path: /healthz-kubedns port: 8080 scheme: HTTP initialDelaySeconds: 60 timeoutSeconds: 5 successThreshold: 1 failureThreshold: 5 readinessProbe: httpGet: path: /readiness port: 8081 scheme: HTTP # we poll on pod startup for the Kubernetes master service and # only setup the /readiness HTTP server once that's available. initialDelaySeconds: 3 timeoutSeconds: 5 args: # command = "/kube-dns" - --domain=cluster.local. - --dns-port=10053 - --kube-master-url=http://10.0.251.148:8080 ports: - containerPort: 10053 name: dns-local protocol: UDP - containerPort: 10053 name: dns-tcp-local protocol: TCP - name: dnsmasq image: gcr.io/google_containers/kube-dnsmasq-amd64:1.4.1 imagePullPolicy: IfNotPresent livenessProbe: httpGet: path: /healthz-dnsmasq port: 8080 scheme: HTTP initialDelaySeconds: 60 timeoutSeconds: 5 successThreshold: 1 failureThreshold: 5 args: - --cache-size=1000 - --no-resolv - --server=127.0.0.1#10053 - --log-facility=- ports: - containerPort: 53 name: dns protocol: UDP - containerPort: 53 name: dns-tcp protocol: TCP - name: healthz image: gcr.io/google_containers/exechealthz-amd64:1.2 imagePullPolicy: IfNotPresent resources: limits: memory: 50Mi requests: cpu: 10m # Note that this container shouldn't really need 50Mi of memory. The # limits are set higher than expected pending investigation on #29688. # The extra memory was stolen from the kubedns container to keep the # net memory requested by the pod constant. memory: 50Mi args: - --cmd=nslookup kubernetes.default.svc.cluster.local. 127.0.0.1 >/dev/null - --url=/healthz-dnsmasq - --cmd=nslookup kubernetes.default.svc.cluster.local. 127.0.0.1:10053 >/dev/null - --url=/healthz-kubedns - --port=8080 - --quiet ports: - containerPort: 8080 protocol: TCP dnsPolicy: Default # Don't use cluster DNS. [root@k8s-master dns14]# cat kube-dns-svc_14.yaml 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: 10.254.10.2 ports: - name: dns port: 53 protocol: UDP - name: dns-tcp port: 53 protocol: TCP [root@k8s-master dns14]#
2.4 下载镜像
docker pull gcr.io/google_containers/kubedns-amd64:1.8 docker pull gcr.io/google_containers/kube-dnsmasq-amd64:1.4.1 docker pull gcr.io/google_containers/exechealthz-amd64:1.2
3、启动
[root@k8s-master dns14]# kubectl create -f kube-dns-rc_14.yaml replicationcontroller "kube-dns-v20" created [root@k8s-master dns14]# kubectl create -f kube-dns-svc_14.yaml service "kube-dns" created
4、验证
注意，以下演示中的web-0与web-1是两个“Named Pod”，是通过创建PetSet创建出来的Pod。详细介绍请参见后续文章。
[root@k8s-master dns14]# kubectl get pod -o wide NAME READY STATUS RESTARTS AGE IP NODE frontend-service-1988680557-xuysd 1/1 Running 0 3h 10.0.82.5 k8s-node-4 web-0 1/1 Running 0 3h 10.0.28.3 k8s-node-1 web-1 1/1 Running 0 3h 10.0.82.6 k8s-node-4 [root@k8s-master dns14]# kubectl get svc mysql-service NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE mysql-service 10.254.194.71 <nodes> 3306/TCP 4h [root@k8s-master dns14]# kubectl exec -ti frontend-service-1988680557-xuysd /bin/bash [root@frontend-service-1988680557-xuysd /]# nslookup web-0.nginx Server: 10.254.10.2 Address: 10.254.10.2#53 Name: web-0.nginx.default.svc.cluster.local Address: 10.0.28.3 [root@frontend-service-1988680557-xuysd /]# nslookup web-1.nginx Server: 10.254.10.2 Address: 10.254.10.2#53 Name: web-1.nginx.default.svc.cluster.local Address: 10.0.82.6 [root@frontend-service-1988680557-xuysd /]# nslookup web-1.nginx.default.svc.cluster.local Server: 10.254.10.2 Address: 10.254.10.2#53 Non-authoritative answer: Name: web-1.nginx.default.svc.cluster.local Address: 10.0.82.6 [root@frontend-service-1988680557-xuysd /]# nslookup mysql-service Server: 10.254.10.2 Address: 10.254.10.2#53 Name: mysql-service.default.svc.cluster.local Address: 10.254.194.71