Edit by @antonfirsov: This is caused by stalled DNS resolution attempts, see #81023 (comment).

Description

We have a small web application that started sporadically throwing TaskCancelledException's after migration from .NET5 to .NET6 and later .NET7. The application consists of just one controller method that retrieves image from Amazon S3, resizes it and saves a resized copy back to S3. The application works fine under .NET5, but under .NET6 and .NET7 it sporadically throws thousands of TaskCancelledException errors from method HttpConnectionPool+HttpConnectionWaiter`1+

Configuration

• Version: .NET6+
• OS version: Alpine Linux 3.16
• Architecture: x64

Regression?

This is a regression in .NET6+ compared to .NET5.

Data

Dump files captured during one of the incidents contain thousands of async calls looking like

.00007f0f9ec03878 (0) System.Net.Http.HttpConnectionPool+HttpConnectionWaiter`1+<WaitForConnectionAsync>d__5[[System.__Canon, System.Private.CoreLib]]
..00007f0f9ec03918 (4) System.Net.Http.HttpConnectionPool+<SendWithVersionDetectionAndRetryAsync>d__84
...00007f0f9ec03a38 (0) System.Net.Http.DiagnosticsHandler+<SendAsyncCore>d__10
....00007f0f9ec03b00 (0) System.Net.Http.HttpClient+<<SendAsync>g__Core|83_0>d
.....00007f0f9ec03bc0 (0) Amazon.Runtime.HttpWebRequestMessage+<GetResponseAsync>d__20

and

.00007f0f9ec1c840 (1) System.Net.Http.HttpConnectionPool+<ConnectToTcpHostAsync>d__99
..00007f0f9ec1c910 (0) System.Net.Http.HttpConnectionPool+<ConnectAsync>d__98
...00007f0f9ec1c9d8 (0) System.Net.Http.HttpConnectionPool+<CreateHttp11ConnectionAsync>d__100
....00007f0f9ec1ca98 (0) System.Net.Http.HttpConnectionPool+<AddHttp11ConnectionAsync>d__74

The events from a trace captured using System.Net.Http provider:
dotnet_20230119_154543_2847c867.9.excel.xlsx

Analysis

Tracing some of the failed requests to connections using ActivityID shows that the corresponding connection was established and closed, but not used for some reason.
This issue may be related.