How to allow large file uploads (>50 MB) in ASP.NET Core 6/7 Web API hosted on Azure App Service

Question

I have an ASP.NET Core 6/7 Web API with an endpoint that uploads files using multipart/form-data. I want to allow files of 50 MB or larger.

I'm currently testing with cURL:

curl -X POST "https://xxxx/v1/Cons/attachments" \
  -H "accept: text/plain" \
  -H "x-api-key: <api-key>" \
  -H "Authorization: Bearer <token>" \
  -H "Content-Type: multipart/form-data" \
  -F "[email protected];type=application/pdf" \
  -F "userId=xxx" \

However, when I try to upload larger files, I get:

HTTP Error 413.1 – Request Entity Too Large

What I've tried:

Kestrel settings in Program.cs:

webBuilder.ConfigureKestrel(options =>
    {
        options.Limits.MaxRequestBodySize = 524288000; // 500 MB
    });

Controller attributes:

[RequestSizeLimit(524288000)]
[RequestFormLimits(MultipartBodyLengthLimit = 524288000)]
[HttpPost("attachments")]
public async Task<IActionResult> Upload([FromForm] ConstructionAttachmentModel model)
{
    // handle file
}

Web.config (for IIS layer, after publishing):

<system.webServer>
    <security>
        <requestFiltering>
            <requestLimits maxAllowedContentLength="524288000" />
        </requestFiltering>
    </security>
</system.webServer>

Azure App Service application setting:

Key:  ASPNETCORE_MAXREQUESTBODYSIZE
Value: 524288000

Question

After all these changes, my API still returns 413.1 for large uploads on Azure app service.

How can I reliably allow file uploads > 50 MB in an ASP.NET Core 6/7 Web API on Azure?

Additional info:

ASP.NET Core 6/7
Web API deployed to Azure App Service
Testing with cURL and Postman
Local Kestrel upload works fine

Code 413 Undocumented, Error: Request Entity Too Large, Response body The page was not displayed because the request entity is too large. — Deva
– Deva, Commented Oct 13 at 8:00

Alparslan ŞEN · Accepted Answer · 2025-10-13 08:16:23Z

1

It looks like there might be a small issue with your web.config structure.

<configuration>
  <system.webServer>
    <security>
      <requestFiltering>        
        <requestLimits maxAllowedContentLength="524288000" />
      </requestFiltering>
    </security>
  </system.webServer>
</configuration>

If <system.webServer> isn’t correctly nested under <configuration>,Azure App Service (and IIS) will simply ignore these settings.

According to Microsoft’s official IIS configuration reference the <system.webServer> element is the root element for IIS site- and application-level settings and must be a direct child of <configuration>.

answered Oct 13 at 8:16

Alparslan ŞEN

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