masstransit and multiple bus instances

Question

According to MT documentation each bus instance should have a different queue name.

Am I right to assume that following is correct configuration?

What wires the WebApi and Backend queue together?

Consider even more advanced scenario

When I design my backend pipeline to use message processing as well I can later slice it and let it use over the wire transport quite easilly. Question is, can I somehow configure MT so the Azure configured Bus relays the messages to the bus configured with local transport?

Answer 1

I'm going to answer this in the context of MassTransit v3, which supports both Azure Service Bus and RabbitMQ. If you are going to use Azure, I'd highly recommend v3 over the transport for v2.

First, about requests. They should be sent, not published. They are usually commands by nature, and not events. The only reason I see people publishing requests is that they don't have the endpoint address of the service. So knowing the endpoint helps, a lot.

Secondly, in your example, every WebAPI instance should have it's own queue to receive responses, since they are sent back to the requestor. With MT3, every IBus instance has a unique auto-delete queue that is setup for this very purpose, to handle responses from requests.

There is a sample, Sample-RequestResponse, in the MassTransit repository on GitHub, that shows how this is setup with RabbitMQ. It's about the same with Azure Service Bus.

The "fabric" that brings it all together is the virtual host (in RabbitMQ) or the namespace (in ASB). The connections between topics and queues determine how it all works together to form a logical bus.