在域句柄中使用多个IP，如何处理失败的IP？

I am trying to coordinate the move of a site from its current server to a new one. My original plan was to migrate the data to the new machine, which is already in place and the migration scripts tested successfully. I was planning to configure the original machine to proxy all requests to the new one, in order to ensure that anyone hitting the original machine before the DNS change fully propagates will still get proper response.I am trying to coordinate the move of a site fr