Update

The problem described below has been answered on the community forum of mongodb.
As stated there Azure Serverless requires setting the TCP timeout to 120 seconds for the machine running the code.

After setting the TCP timeout to 120seconds the timeouts DID NOT occur anymore!

MongoDB timeouts on insert

This repo holds the example application to demonstrate the timeouts we are experiencing when using MongoDB Atlas with Azure Serverless.

Atlas backend	Logs	Result
Azure Serverless (hosted in NL)	logs/azure-serverless-log-try1.txt logs/azure-serverless-log-try2.txt logs/azure-serverless-log-try3.txt logs/azure-serverless-log-try4.txt logs/azure-serverless-log-try5.txt logs/azure-serverless-log-try6.txt	NOK
Azure Dedicated M30 (hosted in NL)	logs/azure-dedicated-m30-log.txt	OK
Google Serverless (hosted in BE)	logs/google-serverless-log.txt	OK

NOK for Azure Serverless is because, sometimes the application takes very long to insert the document.
Then we see times of: Completed in 953285ms this is 15+ minutes.....

What does the application do

1. Create a connection to MongoDB Atlas (with the provided connectionString)
2. Enable debug logging for Mongo Driver
3. Insert a very simple document every 5 minutes
4. Report the time needed to insert the document
5. If the insert takes longer then 5 seconds stop and alert

Tested with:

• net7
• MongoDB.Driver version 2.19.0

Normal output/log of 1 insert

dbug: MongoDB.SDAM[0]
      1 Cluster opening

dbug: MongoDB.SDAM[0]
      1 Cluster opened
3/9/2023 5:47:58 PM
Inserting with ref 0ea21353-7472-4256-949f-8fcdf032fa44
dbug: MongoDB.SDAM[0]
      1 Description changed
dbug: MongoDB.SDAM[0]
      1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Server opening
dbug: MongoDB.Connection[0]
      1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Connection pool opening 600000 0 100 2 120000 500
dbug: MongoDB.Connection[0]
      1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Connection pool created 600000 0 100 2 120000 500
dbug: MongoDB.Connection[0]
      1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Connection pool ready
dbug: MongoDB.SDAM[0]
      1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Description changed { ServerId: "{ ClusterId : 1, EndPoint : "Unspecified/timeout-testing-jeff-lb.izjha.mongodb.net:27017" }", EndPoint: "Unspecified/timeout-testing-jeff-lb.izjha.mongodb.net:27017", ReasonChanged: "Initialized", State: "Connected", ServerVersion: , TopologyVersion: , Type: "LoadBalanced", WireVersionRange: "", LastHeartbeatTimestamp: null, LastUpdateTimestamp: "2023-03-09T17:47:58.7237907Z" }
dbug: MongoDB.SDAM[0]
      1 Description changed
dbug: MongoDB.Connection[0]
      1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Connection checkout started
dbug: MongoDB.Connection[0]
      1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Connection adding
dbug: MongoDB.Connection[0]
      1 1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Connection created
dbug: MongoDB.Connection[0]
      1 1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Connection opening
dbug: MongoDB.SDAM[0]
      1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Server opened
dbug: MongoDB.Connection[0]
      1 1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Connection ready
dbug: MongoDB.Connection[0]
      1 1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Connection added
dbug: MongoDB.Connection[0]
      1 1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Connection checked out
dbug: MongoDB.Command[0]
      1 1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 25326 4 1 Command started insert ftp-uploader { "insert" : "uploadstest123", "ordered" : true, "txnNumber" : NumberLong(1), "$db" : "ftp-uploader", "lsid" : { "id" : CSUUID("b9318af2-9d3e-487f-aefd-fd590cec4009") }, "apiVersion" : "1", "documents" : [{ "_id" : ObjectId("640a1bceb81f131c6bbf2952"), "CreatedOn" : ISODate("2023-03-09T17:47:58.68Z"), "ModifiedOn" : null, "SchemaVersion" : 1, "Data" : { "ConnectionId" : "conn-1234", "BlobReference" : CSUUID("0ea21353-7472-4256-949f-8fcdf032fa44"), "Filename" : "testing123.txt", "Status" : "New", "ErrorDescription" : null } }] } 6408d0cb1ff0b2b854a867ab
dbug: MongoDB.Command[0]
      1 1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 25326 4 1 Command succeeded insert 38.4526 { "n" : 1, "ok" : 1.0, "$clusterTime" : { "clusterTime" : Timestamp(1678384079, 1), "signature" : { "hash" : new BinData(0, "gzCDjo7cWc4oUVg1I1P4Oyf89Go="), "keyId" : NumberLong("7206850029133234182") } }, "operationTime" : Timestamp(1678384079, 1) } 6408d0cb1ff0b2b854a867ab
dbug: MongoDB.Connection[0]
      1 1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Connection checking in
dbug: MongoDB.Connection[0]
      1 1 timeout-testing-jeff-lb.izjha.mongodb.net 27017 Connection checked in
Inserted with ref 0ea21353-7472-4256-949f-8fcdf032fa44
Completed in 529ms

When the timeout occurs

dbug: MongoDB.Connection[0]
      1 1 p9cd6-3m-acceptance-lb.izjha.mongodb.net 27017 Connection failed MongoDB.Driver.MongoConnectionException: An exception occurred while receiving a message from the server.
       ---> System.IO.IOException: Unable to read data from the transport connection: Connection timed out.
       ---> System.Net.Sockets.SocketException (110): Connection timed out
         --- End of inner exception stack trace ---
         at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.ThrowException(SocketError error, CancellationToken cancellationToken)
         at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.System.Threading.Tasks.Sources.IValueTaskSource<System.Int32>.GetResult(Int16 token)
         at System.Net.Security.SslStream.EnsureFullTlsFrameAsync[TIOAdapter](CancellationToken cancellationToken)
         at System.Runtime.CompilerServices.PoolingAsyncValueTaskMethodBuilder`1.StateMachineBox`1.System.Threading.Tasks.Sources.IValueTaskSource<TResult>.GetResult(Int16 token)
         at System.Net.Security.SslStream.ReadAsyncInternal[TIOAdapter](Memory`1 buffer, CancellationToken cancellationToken)
         at System.Runtime.CompilerServices.PoolingAsyncValueTaskMethodBuilder`1.StateMachineBox`1.System.Threading.Tasks.Sources.IValueTaskSource<TResult>.GetResult(Int16 token)
         at System.Threading.Tasks.ValueTask`1.ValueTaskSourceAsTask.<>c.<.cctor>b__4_0(Object state)
      --- End of stack trace from previous location ---
         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)
         --- End of inner exception stack trace ---
dbug: MongoDB.Command[0]
      1 1 p9cd6-3m-acceptance-lb.izjha.mongodb.net 27017 35647 5 2 Command failed insert 953047.9342 MongoDB.Driver.MongoConnectionException: An exception occurred while receiving a message from the server.
       ---> System.IO.IOException: Unable to read data from the transport connection: Connection timed out.
       ---> System.Net.Sockets.SocketException (110): Connection timed out
         --- End of inner exception stack trace ---
         at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.ThrowException(SocketError error, CancellationToken cancellationToken)
         at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.System.Threading.Tasks.Sources.IValueTaskSource<System.Int32>.GetResult(Int16 token)
         at System.Net.Security.SslStream.EnsureFullTlsFrameAsync[TIOAdapter](CancellationToken cancellationToken)
         at System.Runtime.CompilerServices.PoolingAsyncValueTaskMethodBuilder`1.StateMachineBox`1.System.Threading.Tasks.Sources.IValueTaskSource<TResult>.GetResult(Int16 token)
         at System.Net.Security.SslStream.ReadAsyncInternal[TIOAdapter](Memory`1 buffer, CancellationToken cancellationTo... 640855d4039f92600d14c171

For more details see the log files in the logs directory. Above log is from logs/azure-serverless-log-try2.txt.