模块功能：

ngx_cache_purge is nginx module which adds ability to purge content from FastCGI, proxy, SCGI and uWSGI caches. A purge operation removes the content with the same cache key as the purge request has.
可以通过请求URL的方式来清理缓存，让缓存失效

proxy_cache_purge

syntax: proxy_cache_purge on|off|<method> [purge_all] [from all|<ip> [.. <ip>]]
default: none
context: http, server, location
Allow purging of selected pages from proxy's cache.

配置案例：

http {
    proxy_cache_path  /tmp/cache  keys_zone=tmpcache:10m;

    server {
        location / {
            proxy_pass         http://127.0.0.1:8000;
            proxy_cache        tmpcache;
            proxy_cache_key    $uri$is_args$args;
        }

        location ~ /purge(/.*) {
            allow              127.0.0.1;
            deny               all;
            proxy_cache_purge  tmpcache $1$is_args$args;
        }
    }
}

更多详见：ngx_cache_purge