Sitecore 9.1 XDB migration issue with Mongo db connection

Question

I have:

• Sitecore 9.1
• Sitecore 8.2
• MongoDB 3.4
• xDB Data Migration Tool 2.1

I'm trying migrate analytics, I configured tenant and other things by documentations and all looks fine, also Mongo db has "Connection was successfully established." when i run troubleshooter. But when i start "MongoDB Contacts to xConnect Migration" pipeline i have this error:

[Data Exchange] A timeout occured after 30000ms selecting a server using CompositeServerSelector{ Selectors = MongoDB.Driver.MongoClient+AreSessionsSupportedServerSelector, LatencyLimitingServerSelector{ AllowedLatencyRange = 00:00:00.0150000 } }. Client view of cluster state is { ClusterId : "1", ConnectionMode : "Automatic", Type : "Unknown", State : "Disconnected", Servers : [{ ServerId: "{ ClusterId : 1, EndPoint : "Unspecified/localhost:27017" }", EndPoint: "Unspecified/localhost:27017", State: "Disconnected", Type: "Unknown", HeartbeatException: "MongoDB.Driver.MongoConnectionException: An exception occurred while opening a connection to the server. ---> System.TypeLoadException: Could not load type 'MongoDB.Bson.Serialization.Serializers.ElementAppendingSerializer`1' from assembly 'MongoDB.Bson, Version=2.4.4.0, Culture=neutral, PublicKeyToken=null'.
   at MongoDB.Driver.Core.WireProtocol.CommandWireProtocol`1.WrapCommandForQueryMessage(ConnectionDescription connectionDescription, Boolean& messageContainsSessionId)
   at MongoDB.Driver.Core.WireProtocol.CommandWireProtocol`1.CreateMessage(ConnectionDescription connectionDescription, Boolean& messageContainsSessionId)
   at MongoDB.Driver.Core.WireProtocol.CommandWireProtocol`1.<ExecuteAsync>d__15.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MongoDB.Driver.Core.Connections.ConnectionInitializer.<InitializeConnectionAsync>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MongoDB.Driver.Core.Connections.BinaryConnection.<OpenHelperAsync>d__48.MoveNext()
   --- End of inner exception stack trace ---
   at MongoDB.Driver.Core.Connections.BinaryConnection.<OpenHelperAsync>d__48.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MongoDB.Driver.Core.Servers.ServerMonitor.<HeartbeatAsync>d__27.MoveNext()" }] }. (pipeline: Read Contacts from MongoDB Pipeline, pipeline step: Read Contacts from MongoDB, pipeline step identifier: 58da59cb-2fbb-46ec-9cce-602c8c50b761)
ManagedPoolThread #2 09:19:30 ERROR [Data Exchange]    at MongoDB.Driver.Core.Clusters.Cluster.ThrowTimeoutException(IServerSelector selector, ClusterDescription description)
   at MongoDB.Driver.Core.Clusters.Cluster.WaitForDescriptionChangedHelper.HandleCompletedTask(Task completedTask)
   at MongoDB.Driver.Core.Clusters.Cluster.WaitForDescriptionChanged(IServerSelector selector, ClusterDescription description, Task descriptionChangedTask, TimeSpan timeout, CancellationToken cancellationToken)
   at MongoDB.Driver.Core.Clusters.Cluster.SelectServer(IServerSelector selector, CancellationToken cancellationToken)
   at MongoDB.Driver.MongoClient.AreSessionsSupportedAfterServerSelection(CancellationToken cancellationToken)
   at MongoDB.Driver.MongoClient.AreSessionsSupported(CancellationToken cancellationToken)
   at MongoDB.Driver.OperationExecutor.StartImplicitSession(CancellationToken cancellationToken)
   at MongoDB.Driver.MongoCollection.UsingImplicitSession[TResult](Func`2 func)
   at MongoDB.Driver.MongoCursor.Count()
   at Sitecore.DataExchange.Providers.MongoDB.Processors.PipelineSteps.ReadMongoDBDocumentsStepProcessor.LogQueryStatistics(IMongoQuery query, MongoCollection`1 collection, Endpoint endpoint, PipelineStep pipelineStep, PipelineContext pipelineContext, ILogger logger)
   at Sitecore.DataExchange.Providers.MongoDB.Processors.PipelineSteps.ReadMongoDBDocumentsStepProcessor.ReadData(Endpoint endpoint, PipelineStep pipelineStep, PipelineContext pipelineContext, ILogger logger)

My mongo db connection string is mongodb://localhost:27017/analytics, this connection string work fine for sitecore 8.2.

Might be someone know how to solve it?

Answer 1

The error message says that it's trying to load MongoDB.Bson, Version=2.4.4.0. It seems that on your Sitecore instance this DLL has somehow been downgraded incorrectly. You need to make sure MongoDB version 2.6.1.0 is referenced.

Check that all your nuget packages are not downgrading or upgrading Sitecore's default DLL's. You can find the default assembly list on the "Assembly list" link here.