通过nginx来进行代理配置，首先想到的就是使用其负载均衡均衡的功能(upstream)对两个域名进行主备配置：

upstream mytarget
 {
     server aaa.target.com:443 max_fails=30 fail_timeout=300s;
     server bbb.target.com:443 backup;
 }
  server {
         listen       8901;
         server_name  target.server;
         
         location /login/ {
             proxy_pass https://aaa.target.com/my_target/login/;
             #proxy_pass https://bbb.target.com/my_target/login/;
         }
    }