Requests timing out for no clear reason

[SteveVaneeckhout]

I have a yarp 2.3.0 instance running on a VM in front of an Azure App Service. Sometimes, connections to the yarp instance start timing out and I get a notification from our monitoring tool. While this happens, I can access the website directly on the App Service just fine. But the proxyserver keeps the site offline for about 8-12 minutes. This is what the logs show:

Yarp.ReverseProxy.Forwarder.HttpForwarder[48]
RequestTimedOut: The request timed out before receiving a response.
System.Threading.Tasks.TaskCanceledException: The operation was canceled.
   at System.Net.Http.Http2Connection.Http2Stream.<>c.<WaitForDataAsync>b__88_0(Object s, CancellationToken cancellationToken)
   at System.Threading.CancellationTokenSource.ExecuteCallbackHandlers(Boolean throwOnFirstException)
   at System.Threading.TimerQueueTimer.Fire(Boolean isThreadPool)
   at System.Threading.TimerQueue.FireNextTimers()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()
   at System.Threading.PortableThreadPool.WorkerThread.WorkerThreadStart()
--- End of stack trace from previous location ---
   at System.Net.Http.Http2Connection.Http2Stream.System.Threading.Tasks.Sources.IValueTaskSource.GetResult(Int16 token)
   at System.Net.Http.Http2Connection.Http2Stream.ReadResponseHeadersAsync(CancellationToken cancellationToken)
   at System.Net.Http.Http2Connection.SendAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.SendWithVersionDetectionAndRetryAsync(HttpRequestMessage request, Boolean async, Boolean doRequestAuth, CancellationT>
   at System.Net.Http.DiagnosticsHandler.SendAsyncCore(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
   at Yarp.ReverseProxy.Forwarder.HttpForwarder.SendAsync(HttpContext context, String destinationPrefix, HttpMessageInvoker httpClient, ForwarderRequestConfig>

Restarting the service in the terminal fixes the issue. Could this have anything to do with DNS in this issue?

VM info:

uname -a
Linux lvo-proxy 6.8.0-1031-azure #36~22.04.1-Ubuntu SMP Tue Jul  1 03:59:37 UTC 2025 aarch64 aarch64 aarch64 GNU/Linux

dotnet --list-runtimes
Microsoft.AspNetCore.App 8.0.17 [/usr/lib/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 8.0.17 [/usr/lib/dotnet/shared/Microsoft.NETCore.App]

[MihaZupan]

Could this have anything to do with #2905?

No, the exception you're seeing is from Http2Connection.Http2Stream.ReadResponseHeadersAsync, so you did have a connection, but YARP didn't get a response from the server in time.

What do you see from the logs on the backend server? Can you see the request at all, or how long it took to process?