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Can IIS be set up to block API Responses over a certain limit?

We have an application that acts as an API Gateway, taking calls and routing them through to other APIs and then relaying the responses.
In our set up, we make sure that developers making API calls don't try and flood us by uploading massive files or sending in excessive JSON payloads. We're now trying to figure out how we make sure that we don't flood them in return if they make an API call that returns too much data.
Is there a way to set up either IIS or an ASP.Net app to refuses API responses over a certain size in the same way that we would refuse an API Request over a certain size?
Just to add an example in clear terms:
If a developer makes an API request to get all of their customers, the API Gateway passes that request to our internal Customers API. If the Customers API responds with a 600MB response, we want to block the response at the API Gateway and then we'll send a response to the developer asking them to change their request to reduce the resultset.

The response has not limit the size. We can limit the response size by add more parameter Content-Length into the response header.
to set Request limit you could set in web.config file:
<system.web>
<httpRuntime maxRequestLength="2147483647" />
or
<system.webServer>
<security>
<requestFiltering>
<requestLimits maxAllowedContentLength="2147483648" />
</requestFiltering>
</security>
</system.webServer>
Or
You could also set below code in web.config:
<configuration>
<system.web.extensions>
<scripting>
<webServices>
<jsonSerialization maxJsonLength="50000000"/>
</webServices>
</scripting>
</system.web.extensions>
</configuration>
maxJsonLength Configures the maximum length of the JSON string.
For more detail, you could refer:
jsonSerialization Element (ASP.NET Settings Schema)
Regards,
jalpa

Unable to call a HTTP POST request having a csv file more than 10000 records

I am calling a Web API from my C# code wherein I am making an HTTPPost request and sending a CSV file containing almost 11000 rows/records.
It works fine when the number of rows is less than 10,000. However, it throws a 400 bad request when records exceed 10,000.
Any suggestions?

If Web API is hosted by IIS, the default upload file size is 4MB.
To increase that limit, you could update web.config settings:
<system.web>
<httpRuntime maxRequestLength="1048576" /> <!-- KB -->
</system.web>
<!-- for IIS 7+ -->
<system.webServer>
<security>
<requestFiltering>
<requestLimits maxAllowedContentLength="1073741824" /> <!-- Byte -->
</requestFiltering>
</security>
</system.webServer>

Resolved my issue. It seems there was no issue with my code to POST the records. It was third party WebAPI's restriction to upload at max 10,000 records.

Handle every request in Application_BeginRequest

As title suggested, how can I achieve that in my webform project? Currently, if a url points towards a file, the server will send the response with that file without ever entering Application_BeginRequest. Even the MapPageRoute method does not change this behavior. Is there a simple solution?

You may wish to set this in your web.config:
<system.webServer>
<modules runAllManagedModulesForAllRequests="true" />
</system.webServer>
So that even static files are processed by ASP.NET.

Increase the maximum request length in a Azure Api App

I have created an Azure Api App which I will use to upload files. These files will be > 4mb hence the need to increase the maximum request length. I have added the following to Web.config:
<system.web>
<httpRuntime executionTimeout="7200" targetFramework="4.5" maxRequestLength="2097152" />
</system.web>
I have also added:
<system.webServer>
<security>
<requestFiltering>
<requestLimits maxAllowedContentLength="2097152000" />
</requestFiltering>
</security>
</system.webServer>
Yet I still get the exception Maximum request length exceeded.. Am I missing something? Is there something else I can try?
Thanks!

Unfortunately, this is not possible yet. Except the limitation on the API App, there is also a limitation on the Gateway which is an ASP.NET app as well. You can change your API App but you cannot change the Gateway.
I know the team is looking into providing a solution to that but I don't have an ETA to share at this point.

Maximum request length exceeded error in file uploading

How to upload the 5mb pdf files using html upload button?when I try upload the 5mb files I get Maximum request length exceeded error?.This problem occurs because the default value for the maxRequestLength parameter in the section of the Machine.config file is 4096 (4 megabytes).So I try to change webconfig file,
<configuration>
<system.web>
<httpRuntime maxRequestLength="102400" executionTimeout="1200" />
</system.web>
</configuration>
If i use like this i got the An existing connection was forcibly closed by the remote host error.my project is hosted with IIS7.So I try to,
<system.webServer>
<security>
<requestFiltering>
<requestLimits maxAllowedContentLength="1048576" />
</requestFiltering>
</security>
</system.webServer>
This way also not allow to upload the 5mb files?How to upload the 5 mb files through HTML Upload button?

trying adding a "0" To the end of your <requestLimits maxAllowedContentLength> value. I think it's in bytes, which means your example sets it to about 1MB.
Here's the doc on this setting.

If you are running this on a shared hosting account, chances are less that you will be able to resolve this. Due to limited resource allocation, hosting providers specify the timeout for a connection so if the connection takes too much time, it closes it.
My advice is, you should seek help of your hosting provider or try changing the host or plan.

Assuming this is your own server, if not see Murtuza Kabul.
Try
requestLengthDiskThreshold="800000"
Btw I would recommend NeatUpload because the HTML Upload isn't very good in my opinion.