[CentOS-mirror] How to redirect yum requests to another domain

Hi, everyone

I'm trying to redirect requests to another server.
While using conf below(in Nginx):

        location ~* ^/(centos) {
        rewrite ^/(.*)$ http://b.mirrors.lanunion.org/$1 redirect;
        }

I got an error like this:
failure: repodata/repomd.xml from base: [Errno 256] No more mirrors to try.
http://mirrors.cqu.edu.cn/centos/7/os/x86_64/repodata/repomd.xml: [Errno 14] HTTPS Error 301 - Moved Permanently

What can I do to achieve this?

Many thanks.
Tan
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