limit_rate

Limits the rate of response transmission to a client. The rate is specified in bytes per second. The zero value disables rate limiting. The limit is set per a request, and so if a client simultaneously opens two connections, the overall rate will be twice as much as the specified limit.

Rate limit can also be set in the $limit_rate variable. It may be useful in cases where rate should be limited depending on a certain condition:

server {

    if ($slow) {
        set $limit_rate 4k;
    }

    ...
}

Rate limit can also be set in the “X-Accel-Limit-Rate” header field of a proxied server response. This capability can be disabled using the proxy_ignore_headers, fastcgi_ignore_headers, uwsgi_ignore_headers, and scgi_ignore_headers directives.