09-1.部署 coredns 插件

下载新版本的 kubernetes

  1. mkdir -p /opt/k8s/work/kubernetes-v1.11.2
  2. cd /opt/k8s/work/kubernetes-v1.11.2
  3. wget https://dl.k8s.io/v1.11.2/kubernetes-server-linux-amd64.tar.gz
  4. tar -xzvf kubernetes-server-linux-amd64.tar.gz
  5. cd kubernetes
  6. tar -xzvf  kubernetes-src.tar.gz

修改配置文件

coredns 对应的目录是：/opt/k8s/work/kubernetes-v1.11.2/kubernetes/cluster/addons/dns/coredns。

  1. source /opt/k8s/bin/environment.sh
  2. cd /opt/k8s/work/kubernetes-v1.11.2/kubernetes/cluster/addons/dns/coredns
  3. cp coredns.yaml.base coredns.yaml
  4. sed -i -e "s/__PILLAR__DNS__DOMAIN__/${CLUSTER_DNS_DOMAIN}/" -e "s/__PILLAR__DNS__SERVER__/${CLUSTER_DNS_SVC_IP}/" coredns.yaml
  • ${CLUSTER_DNS_DOMAIN} 值为末尾不带点号的 cluster.local

创建 coredns

  1. kubectl create -f coredns.yaml

设置副本数为 3，提高可用性

  1. kubectl patch deploy coredns -n kube-system -p '{"spec": {"replicas": 3}}'

检查 coredns 功能

  1. $ kubectl get all -n kube-system
  2. NAME             DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
  3. deploy/coredns   1         1         1            1           24s
  5. NAME                    DESIRED   CURRENT   READY     AGE
  6. rs/coredns-6c64b7d656   1         1         1         24s
  8. NAME             DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
  9. deploy/coredns   1         1         1            1           24s
  11. NAME                    DESIRED   CURRENT   READY     AGE
  12. rs/coredns-6c64b7d656   1         1         1         24s
  14. NAME                          READY     STATUS    RESTARTS   AGE
  15. po/coredns-6c64b7d656-zgpb8   1/1       Running   0          24s
  17. NAME           TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)         AGE
  18. svc/kube-dns   ClusterIP   10.254.0.2   <none>        53/UDP,53/TCP   24s

新建一个 Deployment

  1. cd /opt/k8s/work
  2. cat > my-nginx.yaml <<EOF
  3. apiVersion: extensions/v1beta1
  4. kind: Deployment
  5. metadata:
  6.   name: my-nginx
  7. spec:
  8.   replicas: 2
  9.   template:
  10.     metadata:
  11.       labels:
  12.         run: my-nginx
  13.     spec:
  14.       containers:
  15.       - name: my-nginx
  16.         image: nginx:1.7.9
  17.         ports:
  18.         - containerPort: 80
  19. EOF
  20. kubectl create -f my-nginx.yaml

Export 该 Deployment, 生成 my-nginx 服务：

  1. $ kubectl expose deploy my-nginx
  2. service "my-nginx" exposed
  4. $ kubectl get services --all-namespaces |grep my-nginx
  5. default       my-nginx     ClusterIP   10.254.0.140     <none>        80/TCP          4s

创建另一个 Pod，查看 /etc/resolv.conf 是否包含 kubelet 配置的 --cluster-dns 和 --cluster-domain，是否能够将服务 my-nginx 解析到上面显示的 Cluster IP 10.254.9.189：

  1. cd /opt/k8s/work
  2. cat > dnsutils-ds.yaml <<EOF
  3. apiVersion: v1
  4. kind: Service
  5. metadata:
  6.   name: dnsutils-ds
  7.   labels:
  8.     app: dnsutils-ds
  9. spec:
  10.   type: NodePort
  11.   selector:
  12.     app: dnsutils-ds
  13.   ports:
  14.   - name: http
  15.     port: 80
  16.     targetPort: 80
  17. ---
  18. apiVersion: extensions/v1beta1
  19. kind: DaemonSet
  20. metadata:
  21.   name: dnsutils-ds
  22.   labels:
  23.     addonmanager.kubernetes.io/mode: Reconcile
  24. spec:
  25.   template:
  26.     metadata:
  27.       labels:
  28.         app: dnsutils-ds
  29.     spec:
  30.       containers:
  31.       - name: my-dnsutils
  32.         image: tutum/dnsutils:latest
  33.         command:
  34.           - sleep
  35.           - "3600"
  36.         ports:
  37.         - containerPort: 80
  38. EOF
  39. kubectl create -f dnsutils-ds.yaml

等待，直到 dnsutils Pod 处于 Running 状态

  1. $ kubectl get pods |grep dnsutils
  2. dnsutils-ds-58897          1/1       Running   0          28s
  3. dnsutils-ds-jkp9v          1/1       Running   0          28s
  4. dnsutils-ds-mvknd          1/1       Running   0          28s
  1. $ kubectl exec -it dnsutils-ds-58897 cat /etc/resolv.conf
  2. nameserver 10.254.0.2
  3. search default.svc.cluster.local svc.cluster.local cluster.local 4pd.io
  4. options ndots:5
  6. $ kubectl exec -it dnsutils-ds-58897 nslookup kubernetes
  7. Server:         10.254.0.2
  8. Address:        10.254.0.2#53
  10. Name:   kubernetes.default.svc.cluster.local
  11. Address: 10.254.0.1
  13. $ kubectl exec -it dnsutils-ds-58897 nslookup my-nginx
  14. Server:         10.254.0.2
  15. Address:        10.254.0.2#53
  17. Name:   my-nginx.default.svc.cluster.local
  18. Address: 10.254.0.140
  • 使用 busybox 镜像中的 nslookup 解析域名失败，但是 alpine 和 tutum/dnsutils 可以正常解析，应该是 busybox 的问题；

参考

https://community.infoblox.com/t5/Community-Blog/CoreDNS-for-Kubernetes-Service-Discovery/ba-p/8187 https://coredns.io/2017/03/01/coredns-for-kubernetes-service-discovery-take-2/ https://www.cnblogs.com/boshen-hzb/p/7511432.html https://github.com/kubernetes/kubernetes/tree/master/cluster/addons/dns https://github.com/kubernetes/dns/issues/109