4.9 Flow-restricting functionality
When the Web server load increases due to an increase in Web server access or impact of a business application, a functionality called flow-restricting functionality maintains the efficiency of Web service process by restricting the number of users who access the Web site.
You can use flow-restricting functionality by embedding the mod_hws_qos module in HTTP Server. You can achieve the following by using the flow-restricting functionality. Note that in the following description, the number of server processes indicates the number of server threads in the UNIX version of HTTP Server when using the worker MPM module and the number of server threads in the Windows version of HTTP Server.
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You can restrict the number of users who access to the Web site at the same time if you restrict the number of server processes that execute the request processes. When there is a high load, the server immediately returns a denial response for the request that exceeds the restricted value and redirects the request to another server. In this way you can maintain the response time.
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You can use session management with cookies to deny a new request when the server is highly loaded and can maintain the response time for the users who are already accessing the server.
For providing an adequate amount of Web service, you need a sufficient number of server processes that can satisfy the number of users accessing the Web service at the same time. If one Web server is not enough, arrange for multiple Web servers, distribute the access by load distribution functionality, and design the operation for assured Web services.
As mentioned above, prepare the Web service resources, and also use the flow-restricting functionality to prepare for the temporary overloaded status. The following figure shows an overview of flow-restricting functionality using mod_hws_qos:
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![[Figure]](GRAPHICS/ZU040500.GIF)
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