Application cannot reconnect to Mongo Atlas after upgrading from M0 to M10

Hi,
We have a .NET 6.0 application running on Kubernetes using a MongoDB.Driver version 2.15.0. We have a Mongo Atlas M0 tier cluster which we are upgrading to M10 to get access to some of its features.
The problem is that when the upgrade happens, application cannot reconnect to M10 by its own and we have to restart a service (by deleting a K8s pod basically).
We have lots of services spread among multiple teams, so it can be cumbersome to sync all of them to restart at once + we have a downtime possibility here.

Exception message we are getting:

A timeout occurred after 30000ms selecting a server using CompositeServerSelector{ Selectors = ReadPreferenceServerSelector{ ReadPreference = { Mode : Primary } }, LatencyLimitingServerSelector{ AllowedLatencyRange = 00:00:00.0150000 }, OperationsCountServerSelector }. Client view of cluster state is { ClusterId : "1", ConnectionMode : "ReplicaSet", Type : "ReplicaSet", State : "Connected", Servers : [{ ServerId: "{ ClusterId : 1, EndPoint : "<sensitive>" }", EndPoint: "<sensitive>", ReasonChanged: "Heartbeat", State: "Connected", ServerVersion: , TopologyVersion: { "processId" : ObjectId("<sensitive>"), "counter" : NumberLong(5) }, Type: "ReplicaSetSecondary", Tags: "{ nodeType : ELECTABLE, region : US_EAST, workloadType : OPERATIONAL, provider : AZURE }", WireVersionRange: "[0, 17]", LastHeartbeatTimestamp: "2023-03-07T10:18:46.4085885Z", LastUpdateTimestamp: "2023-03-07T10:18:46.4085892Z" }, { ServerId: "{ ClusterId : 1, EndPoint : "<sensitive>" }", EndPoint: "<sensitive>", ReasonChanged: "Heartbeat", State: "Connected", ServerVersion: , TopologyVersion: { "processId" : ObjectId("<sensitive>"), "counter" : NumberLong(4) }, Type: "ReplicaSetSecondary", Tags: "{ region : US_EAST, workloadType : OPERATIONAL, nodeType : ELECTABLE, provider : AZURE }", WireVersionRange: "[0, 17]", LastHeartbeatTimestamp: "2023-03-07T10:18:47.8866555Z", LastUpdateTimestamp: "2023-03-07T10:18:47.8866558Z" }, { ServerId: "{ ClusterId : 1, EndPoint : "<sensitive>" }", EndPoint: "<sensitive>", ReasonChanged: "ReportedPrimaryIsStale", State: "Disconnected", ServerVersion: , TopologyVersion: , Type: "Unknown", LastHeartbeatTimestamp: null, LastUpdateTimestamp: "2023-03-07T10:18:46.3312199Z" }] }.

Connection string: mongodb+srv://username:password@[database].[id].mongodb.net

Hi, @Proxi,

Welcome to the MongoDB Community Forums.

I understand that your .NET 6.0 applications running MongoDB .NET/C# Driver 2.15.0 are failing to maintain connectivity to your Atlas cluster while upgrading from M0 to M10. You also note that your services are running in Kubernetes.

This is unexpected. The 2.15.0 release included a fix for a DnsClient.NET issue that caused problems with DNS resolution in k8s environments. Subsequent releases have not included any additional DNS-related fixes. See CSHARP-4001 for more information on the DnsClient.NET issue fixed in 2.15.0.

I would recommend reaching out to MongoDB Atlas Support to assist in troubleshooting further.

Sincerely,
James