nginx 反向代理问题（单 ip 单端口多子域名）

现在有这样的问题
之前主机是基于server_name来解决这个问题的。
但是现在使用nginx做反向代理试了好几种方法好像都没办法解决这个问题，以下是我的配置清单。

upstream nginxdjango {
server 222.222.222.222:80;
}
server {

listen 80;
server_name www.aa.com;
access_log /var/log/aaproxy.access.log main;
error_log /var/log/aaproxy.error.log;
root html;
index index.html index.htm;
location / {
proxy_pass http://nginxdjango;
proxy_redirect off;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_next_upstream error timeout invalid_header http_500 http_502 http_503 http_504;
proxy_max_temp_file_size 0;
    proxy_connect_timeout      90;
    proxy_send_timeout         90;
    proxy_read_timeout         90;
    proxy_buffer_size          4k;
    proxy_buffers              4 32k;
    proxy_busy_buffers_size    64k;
    proxy_temp_file_write_size 64k;
}

}
server {

listen 80;
    server_name media.aa.com;
    access_log /var/log/aaproxy.access.log main;
    error_log /var/log/aaproxy.error.log;
    root html;
    index index.html index.htm;
    location / {
    proxy_pass http://nginxdjango;
    proxy_redirect off;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_next_upstream error timeout invalid_header http_500 http_502 http_503 http_504;
    proxy_max_temp_file_size 0;
    proxy_connect_timeout      90;
    proxy_send_timeout         90;
    proxy_read_timeout         90;
    proxy_buffer_size          4k;
    proxy_buffers              4 32k;
    proxy_busy_buffers_size    64k;
    proxy_temp_file_write_size 64k;
    }

}
server {

listen 80;
    server_name static.aa.com;
    access_log /var/log/aaproxy.access.log main;
    error_log /var/log/aaproxy.error.log;
    root html;
    index index.html index.htm;
    location / {
    proxy_pass http://nginxdjango;
    proxy_redirect off;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_next_upstream error timeout invalid_header http_500 http_502 http_503 http_504;
    proxy_max_temp_file_size 0;
    proxy_connect_timeout      90;
    proxy_send_timeout         90;
    proxy_read_timeout         90;
    proxy_buffer_size          4k;
    proxy_buffers              4 32k;
    proxy_busy_buffers_size    64k;
    proxy_temp_file_write_size 64k;
    }

}