This module disables keepalive automatically when the http requests are for iso, zip, gz ... files and have refers, e.g. when they are directed from official site to mirror.bjtu.edu.cn to download a software package. In this situation, we need not to still keep-alive for these requests.
Build and install by running in nginx directory:
./configure --add-module=/path/to/ngx_http_auto_keepalive
In main, server or location config:
keepalive_autoclose on;
autoclose_filetypes ".iso .zip";