这个算是很常见的需求了，早前也踩过 dns 无法解析的坑。

在线修改 coredns 的 configmap，不用重启哦。

kubectl edit configmap coredns -n kube-system

apiVersion: v1
data:
  Corefile: |
    .:53 {
        errors
        health
        ready
        kubernetes cluster.local in-addr.arpa ip6.arpa {
          pods insecure
          upstream /etc/resolv.conf
          fallthrough in-addr.arpa ip6.arpa
        }
        hosts {
            192.168.1.122     demo1.xx.com
            192.168.1.123     demo2.xx.com
            fallthrough
        }
        prometheus :9153
        forward . /etc/resolv.conf {
          prefer_udp
        }
        cache 30
        loop
        reload
        loadbalance
    }
kind: ConfigMap
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"v1","data":{"Corefile":".:53 {\n    errors\n    health\n    ready\n    kubernetes cluster.local in-addr.arpa ip6.arpa {\n      pods insecure\n      upstream /etc/resolv.conf\n      fallthrough in-addr.arpa ip6.arpa\n    }\n    prometheus :9153\n    forward . /etc/resolv.conf {\n      prefer_udp\n    }\n    cache 30\n    loop\n    reload\n    loadbalance\n}\n"},"kind":"ConfigMap","metadata":{"annotations":{},"labels":{"addonmanager.kubernetes.io/mode":"EnsureExists"},"name":"coredns","namespace":"kube-system"}}
  creationTimestamp: "2020-06-10T07:50:08Z"
  labels:
    addonmanager.kubernetes.io/mode: EnsureExists
  name: coredns
  namespace: kube-system
  resourceVersion: "566"
  selfLink: /api/v1/namespaces/kube-system/configmaps/coredns
  uid: 61c3ac0c-8aff-4632-b53a-360ac08cda74

参考：
https://www.jianshu.com/p/d421f864732f
https://coredns.io/manual/toc/
https://coredns.io/plugins/hosts/