502 - Web server received an invalid response while acting as a gateway or proxy server.

I had a problem in an ASP.Net web application hosted on IIS 8.0 and there was ARR server to load balance requests.

The error was as follows, sometimes when I hit the URL the below error appears and when I refresh the page the error disappears.

502 - Web server received an invalid response while acting as a gateway or proxy server. There is a problem with the page you are looking for, and it cannot be displayed.

When investigating the issue I found that it was happening randomly and happened always for long requests (when I upload a file or requesting heavy pages).

After lots of searching I found that the error code is 502.2 which related to 

• 502.2 - Bad gateway: Premature Exit.

as per Microsoft error codes for IIS in the below link 

https://docs.microsoft.com/en-us/aspnet/core/publishing/iis#common-errors

And the solution was very simple, Just increase the ARR request timeout as the below screenshots

Important Note: If you are using IIS 7.0 or 7.5 you can take a loot at the below hotfixes from Microsoft, would be helpful

https://support.microsoft.com/en-us/kb/2455129

https://www.microsoft.com/en-us/download/details.aspx?id=30333