upstream 
myhost1 {
server 192.168.1.1:80 weight=1 max_fails=2 fail_timeout=30s;
}
myhost2 {
server 192.168.1.2:80 weight=1 max_fails=2 fail_timeout=30s;
}
#####
server {
 listen 80;
 server_name 
www.xxx.com;
 location /
 {
 proxy_pass 
http://myhost1;
 proxy_cache_key $host$uri$is_args$args;
 proxy_set_header Host $host;
 proxy_set_header X-Forwarded-For $remote_addr;
 proxy_cache_valid 200 304 12h;
 expires 2d;
}
 location ~ /purge(/.*)
 {
 allow 127.0.0.1;
 deny all;
 proxy_cache_purge cache_one $host$1$is_args$args;
 }
 location ~ .*\.(php|jsp|cgi|asp|aspx|flv|swf|xml)?$
 {
 proxy_set_header Host $host;
 proxy_set_header X-Forwarded-For $remote_addr;
 proxy_pass 
http://myhost1;
 }
 access_log off;
 }
server {
 listen 80;
 server_name 
www.yyy.com;
 location /
 {
 proxy_pass 
http://myhost2;
 proxy_cache_key $host$uri$is_args$args;
 proxy_set_header Host $host;
 proxy_set_header X-Forwarded-For $remote_addr;
 proxy_cache_valid 200 304 12h;
 expires 2d;
}
 location ~ /purge(/.*)
 {
 allow 127.0.0.1;
 deny all;
 proxy_cache_purge cache_one $host$1$is_args$args;
 }
 location ~ .*\.(php|jsp|cgi|asp|aspx|flv|swf|xml)?$
 {
 proxy_set_header Host $host;
 proxy_set_header X-Forwarded-For $remote_addr;
 proxy_pass 
http://myhost2;
 }
 access_log off;
 }