如果域名被墙，在大陆无法正常访问时在另一台vps上设置一个备用域名供大陆用户正常使用。

首先需要一台IP在大陆能正常访问的vps.和一个域名。

nginx配置文件：
（请注意替换自己的域名，fedi.bar为主域名。cn.fedi.bar为备用域名）

map $http_upgrade $connection_upgrade {
    default upgrade;
    ''            close;
}
map $http_origin $fedi_site_origin {
    default $http_origin;
    https://cn.fedi.bar https://fedi.bar;
}

map $http_referrer $fedi_site_referrer {
    default '';
    ~^https://cn.fedi.bar/(?<referrer_path>.*)$ https://fedi.bar/$referrer_path;
}
//更改缓存文件夹，此处为/data/cn.fedi.bar/
proxy_cache_path /data/cn.fedi.bar/ levels=1:2 keys_zone=fedi.bar:10m inactive=7d max_size=1g;
server {
    listen 80;
    listen 443 ssl http2;
    server_name fedi.bar cn.fedi.bar;
    if ($scheme = http) { return 301 https://$host$request_uri; }
    keepalive_timeout     70;
    sendfile              on;
    client_max_body_size 100m;

    gzip on;
    gzip_disable "msie6";
    gzip_vary on;
    gzip_proxied any;
    gzip_comp_level 6;
    gzip_buffers 16 8k;
    gzip_http_version 1.1;
    gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;

    location / {
        try_files $uri @proxy;
    }
    
    location @proxy {
        proxy_ssl_server_name on;
        proxy_ssl_protocols TLSv1.2 TLSv1.3;
        proxy_ssl_ciphers HIGH:!MEDIUM:!LOW:!aNULL:!NULL:!SHA;
        proxy_redirect https://fedi.bar https://cn.fedi.bar;
        sub_filter 'https://fedi.bar' 'https://cn.fedi.bar';
        sub_filter '<a href="https://fedi.bar' '<a href="https://cn.fedi.bar';
        sub_filter 'https://fedi.bar/photos/' 'https://cn.fedi.bar/photos/';

        sub_filter_once off;
        proxy_set_header Accept-Encoding "";
        proxy_hide_header Alt-Svc;
        proxy_set_header Host $origin_domain;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header User-Agent $http_user_agent;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_hide_header Content-Security-Policy;
        proxy_set_header Origin $fedi_site_origin;
        proxy_set_header Referer $fedi_site_referrer;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header Proxy "";
        proxy_pass_header Server;
        proxy_cookie_domain https://fedi.bar https://cn.fedi.bar;

        proxy_pass https://127.0.0.1:443;  //替换自己的主服务器的IP
        proxy_buffering on;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection $connection_upgrade;

        proxy_cache fedi.bar;
        proxy_cache_valid 200 7d;
        proxy_cache_valid 410 24h;
        proxy_cache_use_stale error timeout updating http_500 http_502 http_503 http_504;
        add_header X-Cached $upstream_cache_status;
        add_header Strict-Transport-Security "max-age=31536000" always;
        
        tcp_nodelay on;
  }
    
    ssl_certificate /etc/letsencrypt/live/cn.fedi.bar/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/cn.fedi.bar/privkey.pem; # managed by Certbot

}

配置好ssl证书 nginx -s reload 即可。