Description
A web server can only serve a limited number of concurrent requests. QoS is used to ensure that important resources stay available under high server load. mod_qos is used to reject requests to unimportant resources while granting access to more important applications. It is also possible to disable access restrictions, for example, for requests to very important resources or for very important users.
Control mechanisms are available at the following levels:
- Request level control: mod_qos controls the number of concurrent requests to a name space (URL). It is used to define different priorities to different pages or applications within a web server.
- Connection level control: mod_qos controls the number of TCP connections to the web server. This helps limit the connections coming from a single client or from unknown networks, in order to reduce the maximum number of concurrent connections to a virtual server or to implement dynamic HTTP keep-alive settings.
- Bandwidth level control: throttles requests/responses to certain URL on the web server.
- Generic request line and header filter dropping suspicious request URLs or HTTP headers.
The module can be useful when used in a reverse proxy in order to divide up resources to different webserver.
Read more about this topic: Mod Qos
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