Kube-DNS搭建（1.4版本）

振宇要低調發表於2017-03-30

1、介紹

　　之前介紹過DNS的搭建（基於Kubernetes叢集部署skyDNS服務），但那個版本的DNS是隨著Kubernetes1.2釋出出來的，有點原始。本文主要講解Kubernetes1.4版本中的DNS外掛的安裝。與1.2版本相比，1.4中的DNS增加了解析Pod（HostName）對應的域名的新功能，且在部署上也有了一些變化。1.2中，需要部署etcd（或使用master上的Etcd）、kube2sky、skydns三個元件；1.4中，DNS元件由kubedns（監控Kubernetes中service變化）、dnsmasq（DNS服務）和一個健康檢查容器——healthz組成。

　　在搭建PetSet（寵物應用）時，系統首先要為PetSet設定一個HeadLess service，即service的ClusterIP顯示的設定成none，而對每一個有特定名稱的Pet（Named Pod），可以通過其HostName進行定址訪問。這就用到了1.4中的新功能。以下給出具體的搭建過程。

2、修改配置

2.1修改各個node上的kubelet

　　修改以下紅色部分，完成後重啟kubelet服務。

[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

　　修改以下紅色部分：

[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檔案

　　修改以下紅色部分：

[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 下載映象

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、啟動

[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、驗證

　　注意，以下演示中的web-0與web-1是兩個“Named Pod”，是通過建立PetSet建立出來的Pod。詳細介紹請參見後續文章。

[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

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