[ERROR CoreDNSUnsupportedPlugins

在kubernetesji集群从1.16.x版本升级到1.17.x版本地时候报错：

kubeadm upgrade plan
[upgrade/config] Making sure the configuration is correct:
[upgrade/config] Reading configuration from the cluster...
[upgrade/config] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -oyaml'
[preflight] Running pre-flight checks.
[preflight] Some fatal errors occurred:
        [ERROR CoreDNSUnsupportedPlugins]: there are unsupported plugins in the CoreDNS Corefile
[preflight] If you know what you are doing, you can make a check non-fatal with `--ignore-preflight-errors=...`
To see the stack trace of this error execute with --v=5 or higher

问题解决：
1.17.x版本的CoreDNS不支持hosts插件，修改corddns的配置文件，并把hosts部分注释。

kubectl edit cm coredns -n kube-system

保存并退出重新运行升级kubeadm upgrade plan查看。