2 question:
1. i want to put the pic,css,js etc. files on the frontend server, but with below config, i put a tar file to /var/www/a.com/test.tar and visite http://a.com/test.tar it return a 404 herder. how can i fix it?

2. i want control the proxy cache for different cache time with the different request uri, could you give me the right way to config it ? thank you very much.

my nginx.conf

server {
listen 80;
root /var/www/a.com;
server_name a.com;
index index.html index.htm index.php;

location ^~ /admin/ {
proxy_pass http://backend;
}

location ~* ^/post/ {
proxy_cache main;
proxy_cache_valid 200 301 302 60d;
proxy_cache_valid any 30d;
proxy_pass http://backend;
}

location ~* ^/(list|archive)/ {
proxy_cache main;
proxy_cache_valid 200 301 302 60d;
proxy_cache_valid any 1d;
proxy_pass http://backend;
}

location ~ ^.*\.php$ {
proxy_pass http://backend;
}

location / {
proxy_cache main;
proxy_cache_valid any 10m;
proxy_pass http://backend;
}

location ~ .*\.(gif|jpg|jpeg|png|bmp|swf|ico)$ {
expires 30d;
}

}