CoreDNS用于集群内部Service名称解析。

    1. kubectl apply -f coredns.yaml
    2. kubectl get pods -n kube-system 
    3. NAME                          READY   STATUS    RESTARTS   AGE
    4. coredns-5ffbfd976d-j6shb      1/1     Running   0          32s
    5. kube-flannel-ds-amd64-2pc95   1/1     Running   0          38m
    6. kube-flannel-ds-amd64-7qhdx   1/1     Running   0          15m
    7. kube-flannel-ds-amd64-99cr8   1/1     Running   0          26m

    DNS解析测试：

    1. kubectl run -it --rm dns-test --image=busybox:1.28.4 sh
    2. If you don't see a command prompt, try pressing enter.
    3. / # nslookup kubernetes
    4. Server:    10.0.0.2
    5. Address 1: 10.0.0.2 kube-dns.kube-system.svc.cluster.local
    6. Name:      kubernetes
    7. Address 1: 10.0.0.1 kubernetes.default.svc.cluster.local

    解析没问题