08-2. 部署 coredns 插件

如果没有特殊指明，本文档的所有操作均在 zhangjun-k8s-01 节点上执行；

下载和配置 coredns

  1. cd /opt/k8s/work
  2. git clone https://github.com/coredns/deployment.git
  3. mv deployment coredns-deployment

创建 coredns

  1. cd /opt/k8s/work/coredns-deployment/kubernetes
  2. source /opt/k8s/bin/environment.sh
  3. ./deploy.sh -i ${CLUSTER_DNS_SVC_IP} -d ${CLUSTER_DNS_DOMAIN} | kubectl apply -f -

检查 coredns 功能

  1. $ kubectl get all -n kube-system -l k8s-app=kube-dns
  2. NAME                          READY   STATUS    RESTARTS   AGE
  3. pod/coredns-76b74f549-cwm8d   1/1     Running   0          62s
  5. NAME               TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)                  AGE
  6. service/kube-dns   ClusterIP   10.254.0.2   <none>        53/UDP,53/TCP,9153/TCP   62s
  8. NAME                      READY   UP-TO-DATE   AVAILABLE   AGE
  9. deployment.apps/coredns   1/1     1            1           62s
  11. NAME                                DESIRED   CURRENT   READY   AGE
  12. replicaset.apps/coredns-76b74f549   1         1         1       62s

新建一个 Deployment：

  1. cd /opt/k8s/work
  2. cat > my-nginx.yaml <<EOF
  3. apiVersion: apps/v1
  4. kind: Deployment
  5. metadata:
  6.   name: my-nginx
  7. spec:
  8.   replicas: 2
  9.   selector:
  10.     matchLabels:
  11.       run: my-nginx
  12.   template:
  13.     metadata:
  14.       labels:
  15.         run: my-nginx
  16.     spec:
  17.       containers:
  18.       - name: my-nginx
  19.         image: nginx:1.7.9
  20.         ports:
  21.         - containerPort: 80
  22. EOF
  23. 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 my-nginx -o wide
  5. NAME       TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)   AGE   SELECTOR
  6. my-nginx   ClusterIP   10.254.67.218   <none>        80/TCP    5s    run=my-nginx

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 10.254.40.167

  1. cd /opt/k8s/work
  2. cat > dnsutils-ds.yml <<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: apps/v1
  19. kind: DaemonSet
  20. metadata:
  21.   name: dnsutils-ds
  22.   labels:
  23.     addonmanager.kubernetes.io/mode: Reconcile
  24. spec:
  25.   selector:
  26.     matchLabels:
  27.       app: dnsutils-ds
  28.   template:
  29.     metadata:
  30.       labels:
  31.         app: dnsutils-ds
  32.     spec:
  33.       containers:
  34.       - name: my-dnsutils
  35.         image: tutum/dnsutils:latest
  36.         command:
  37.           - sleep
  38.           - "3600"
  39.         ports:
  40.         - containerPort: 80
  41. EOF
  42. kubectl create -f dnsutils-ds.yml
  1. $ kubectl get pods -lapp=dnsutils-ds -o wide 
  2. NAME                READY   STATUS    RESTARTS   AGE   IP               NODE              NOMINATED NODE   READINESS GATES
  3. dnsutils-ds-7h9np   1/1     Running   0          69s   172.30.244.3     zhangjun-k8s-01   <none>           <none>
  4. dnsutils-ds-fthdl   1/1     Running   0          69s   172.30.82.131    zhangjun-k8s-02   <none>           <none>
  5. dnsutils-ds-w69zp   1/1     Running   0          69s   172.30.184.132   zhangjun-k8s-03   <none>           <none>
  1. $ kubectl -it exec dnsutils-ds-7h9np  cat /etc/resolv.conf
  2. search default.svc.cluster.local svc.cluster.local cluster.local 4pd.io
  3. nameserver 10.254.0.2
  4. options ndots:5
  1. $ kubectl -it exec dnsutils-ds-7h9np nslookup kubernetes
  2. Server:         10.254.0.2
  3. Address:        10.254.0.2#53
  5. Name:   kubernetes.default.svc.cluster.local
  6. Address: 10.254.0.1
  1. $ kubectl -it exec dnsutils-ds-7h9np nslookup www.baidu.com
  2. Server:         10.254.0.2
  3. Address:        10.254.0.2#53
  5. Non-authoritative answer:
  6. *** Can't find www.baidu.com: No answer
  1. $ kubectl -it exec dnsutils-ds-7h9np nslookup www.baidu.com.
  2. Server:         10.254.0.2
  3. Address:        10.254.0.2#53
  5. Non-authoritative answer:
  6. www.baidu.com   canonical name = www.a.shifen.com.
  7. Name:   www.a.shifen.com
  8. Address: 220.181.38.150
  9. Name:   www.a.shifen.com
  10. Address: 220.181.38.149
  1. $ kubectl -it exec dnsutils-ds-7h9np nslookup my-nginx
  2. Server:         10.254.0.2
  3. Address:        10.254.0.2#53
  5. Name:   my-nginx.default.svc.cluster.local
  6. Address: 10.254.67.218

参考

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