nginx dynamic mirror

gistfile1.txt

$ curl -H"X-Mirror1: 127.0.0.1:5000" -H"X-Mirror2: 127.0.0.1:5001" -H"X-Mirror3: 127.0.0.1:5002" localhost:8000

nginx.conf

    server {
       listen 8000;
       mirror_request_body on;
#       log_subrequest on;

       root /tmp;
       location / {
          mirror /mirror1;
          mirror /mirror2;
          mirror /mirror3;
       }
       location /mirror1 {
          internal;
          if ($http_x_mirror1 != "") {
            proxy_pass http://$http_x_mirror1$request_uri;
          }
       }
       location /mirror2 {
          internal;
          if ($http_x_mirror2 != "") {
            proxy_pass http://$http_x_mirror2$request_uri;
          }
       }
       location /mirror3 {
          internal;
          if ($http_x_mirror3 != "") {
            proxy_pass http://$http_x_mirror3$request_uri;
          }
       }

    }