Experiencing timeouts with Atlas Serverless cluster

[johnknoop]

Hi

We've been using this library for years with our classic Atlas cluster, but since switching to an Atlas Serverless cluster, we've started seeing intermittent timeout exceptions:

MongoDB.Driver.MongoConnectionException: An exception occurred while receiving a message from the server.
---> System.TimeoutException: The operation has timed out.
at MongoDB.Driver.Core.Misc.StreamExtensionMethods.ReadAsync(Stream stream, Byte[] buffer, Int32 offset, Int32 count, TimeSpan timeout, CancellationToken cancellationToken)
at MongoDB.Driver.Core.Misc.StreamExtensionMethods.ReadBytesAsync(Stream stream, Byte[] buffer, Int32 offset, Int32 count, TimeSpan timeout, CancellationToken cancellationToken)
at MongoDB.Driver.Core.Connections.BinaryConnection.ReceiveBufferAsync(CancellationToken cancellationToken)

The application is an Azure App Service, and the pattern of failures is that all requests succeed until there's a period of idling, after which the next one will timeout.

At first, I didn't consider the possibility that it had anything to do with this library, so I reached out to the MongoDB Atlas team and wondered if they are aware of any issues related to slow cold starts or similar. But they suggested that I try and see if I can reproduce it when creating a MongoClient directly without using this library, so for the last couple of days, I've been switching back and forth and I can indeed confirm that the timeouts only occur when this library is used.

Do you have any clue why this would happen?