The mod_qos module may be used to determine which requests should be served and
which shouldn't in order to avoid resource over-subscription. The module
collects different attributes such as the request URL, HTTP request and response
headers, the IP source address, the HTTP response code, history data (based on
user session and source IP address), the number of concurrent requests to the
server (total or requests having similar attributes), the number of concurrent
TCP connections (total or from a single source IP), and so forth.

Counteractive measures to enforce the defined rules are: request blocking,
dynamic timeout adjustment, request delay, response throttling, and dropping of
TCP connections.