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

[debashish2014]

Hi,

I have written a Console application to do load testing and I am using c# Microsoft.AspNetCore.SignalR.Client.Core.HubConnectionBuilder for creating connections to AspNet Core SignalR application, which is hosted on IIS running on a Windows Server 2012 R2 having 8 Cores and 32 GB RAM.

We have a single Hub in the project, with below method.

public async Task Send(string name, string message)
{
         await Clients.All.SendAsync("BroadcastMessage", name, message);
}

.Net Clr Version of Application pool has been set to No Managed Code.

We are able to reach up to 16000 connections approx. Any subsequent request to the IIS leads to below error:

The application targets .Net Core 2.1

We have tried deploying the applction on a Azure VM (8 Cores, 32 Gb RAM, Windows Server 2016) as well, but the result is same.

IIS configuration appConcurrentRequestLimit has been set to 80000

appcmd.exe set config /section:system.webserver/serverRuntime /appConcurrentRequestLimit:80000

We also tried modifying below Kestrel settings, but ended up in vain.

.UseKestrel(options =>
        {
            options.Limits.MaxConcurrentConnections = 80000;
            options.Limits.MaxConcurrentUpgradedConnections = 80000;
        });

Are we missing anything?

[mikaelm12]

Any ideas here as to why the configured concurrent connection limit isn't respected @pakrym @jkotalik? Thanks!

[pakrym]

Do you have https://docs.microsoft.com/en-us/iis/configuration/system.applicationhost/sites/site/limits maxConnections set?

[MRT-77]

I received 502 error after upgrading the "Hosting Bundle"