To limit the size of client requests, you can modify the maxAllowedContentLength parameter of in web.config, such as setting it to 104857600 (100MB), and synchronizing the maxRequestLength of ASP.NET; to reasonably set the connection timeout time, you can modify it through the IIS Manager or the appcmd.exe command, which is 120 seconds by default, and the API scenario is recommended to set it to 30-90 seconds; if the request queue is full, you can increase MaxClientConn and QueueLength, optimize application performance, and enable load balancing to relieve stress.

When you are running an IIS-based web application, it is critical to properly configure request restrictions and connection timeouts. These settings not only affect the performance of the website, but also directly affect the stability and security of the server.

Here are some common but very practical configuration suggestions to help you better control request processing behavior in IIS.

How to limit the size of client requests?

The default allowable request body size of IIS is limited, usually around 30MB. If your application needs to upload large files or receive large amounts of POST data, you need to manually adjust this limit.

The modification method is as follows:

• Open the web.config file;
• Add or modify the <requestlimits></requestlimits> configuration item under the <system.webserver></system.webserver> node;

For example:

 <system.webServer>
  <security>
    <requestFiltering>
      <requestLimits maxAllowedContentLength="104857600" />
    </requestFiltering>
  </security>
</system.webServer>

maxAllowedContentLength here is in bytes, and the above example is set to 100MB. It should be noted that if ASP.NET's httpRuntime setting is used at the same time, it also needs to modify its maxRequestLength parameter synchronously, otherwise 404 or other strange errors may occur.

How to set the connection timeout more reasonable?

The connection timeout of IIS refers to the maximum time when the server waits for the client to send data after the client establishes a connection with the server. By default, this value is 120 seconds, but may not be enough or too long in some scenarios.

To adjust the connection timeout:

• Open IIS Manager;
• Select your site and double-click "Advanced Settings";
• Find "Connection Timeout (Secs)" and modify it to the value you expect.

Or use appcmd.exe to modify it through the command line:

 %systemroot%\system32\inetsrv\appcmd.exe set config -section:system.applicationHost/sites /siteDefaults.connectionTimeout:"00:01:30"

This command sets the default connection timeout to 90 seconds. If your service is facing API requests, you can shorten this value appropriately, for example, set to 30 seconds to prevent long-term hangs and waste resources.

What should I do if the request queue is full? How to increase the concurrent request upper limit?

When the number of requests received by IIS exceeds its ability to handle, the extra requests will be put into the queue and wait. But if the queue is full, the default error will be returned with 503.

It can be optimized by:

• Increase the request queue length : Modify MaxClientConn and QueueLength in the registry;
• Optimize application performance : reduce the processing time of a single request and avoid blocking threads;
• Enable load balancing : multiple servers share pressure to fundamentally alleviate queuing problems;

Note: It is best to do tests before modifying system-level parameters to avoid unexpected impacts on the production environment.

Let's summarize

Setting request restrictions and connection timeouts can not only improve the server's response efficiency, but also enhance the robustness of the system. The key is to adjust the parameters according to actual business needs, rather than blindly copying the default values.

Basically that's it.

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