Duplicate detection with NServiceBus on Azure Service Buus

Question

I'm using NServiceBus as an abstraction layer for Azure Service Bus (in case we move away from Azure). I find that when working with multiple subscribers (who subscribe to the same events) the number of duplicate messages increases. I know Azure Service Bus (ASB) has a way of detecting these duplicates and I can see that the feature is configurable through NServiceBus (according to documentation). However, I can only get a sample of of achieving duplication detection by means of configuration section. What I require is a sample of how to achieve this with code.

Thanks

Suraj

Answer 1

You can specify configuration using code-based approach as well. NServiceBus has to contracts that can help with that IConfigurationSource and IProvideConfiguration<T>. Here's an example how you can take a configuration file section (UnicastBusConfig) and specify values via code.

Specifically to what you've asked, implementing IProvideConfiguration<AzureServiceBusQueueConfig> will allow you configure ASB transport, specifying duplicates and such.

The observation about number of duplicates increasing as a result of increasing subscribers feels as a symptom, not the problem. That is probably a different question, not related to the configuration. Saying that, I'd look into it prior to enabling the native de-dupplication. While you can specify RequiresDuplicateDetection and DuplicateDetectionHistoryTimeWindow be aware that ASB performing duplicate detection on the ID property only. Also, it is better to build your handlers as idempotent, rather than relying on the native de-duplication.