Why a simple configuration in MassTransit creates 2 queues and 3 exchanges?

Question

I created a MassTransit quickstart program to interact with my localhost RabbitMQ:

namespace ConsoleApp1
{
    public static class Program
    {
        public class YourMessage
        {
            public string Text { get; set; }
        }

        public static async Task Main(params string[] args)
        {
            var bus = Bus.Factory.CreateUsingRabbitMq(sbc =>
            {
                var host = sbc.Host(new Uri("rabbitmq://localhost"), h =>
                {
                    h.Username("guest");
                    h.Password("guest");
                });

                sbc.ReceiveEndpoint(host, "test_queue", ep =>
                {
                    ep.Handler<YourMessage>(async context => await Console.Out.WriteLineAsync($"Received: {context.Message.Text}"));
                });
            });

            await bus.StartAsync(); 
            await bus.Publish(new YourMessage{Text = "Hi"});
            Console.WriteLine("Press any key to exit");
            Console.ReadKey();
            await bus.StopAsync();
        }
    }
}

Everything looked fine untill I actually checked the underlying RabbitMQ management and found out that just for this very simple program, MassTransit created 3 exchanges and 2 queues.

Exchanges, all fanouts:

• ConsoleApp1:Program-YourMessage: Durable
• VP0003748_dotnet_bus_6n9oyyfzxhyx9ybobdmpj8qeyt: Auto-delete and Durable?
• test_queue: Durable

Queues:

• VP0003748_dotnet_bus_6n9oyyfzxhyx9ybobdmpj8qeyt: x-expire 60000
• test_queue: Durable

I would like to know why all of that is necessary or is the default configuration? In particular, I am not really sure to get the point of creating so "many".

Bromleigh

Which version of MassTransit do you use? This issue is reproducible with version 5.5.6, but version 6.0.0 does not create unused auto-delete exchange and queue. As for now, cannot locate commit when it has been fixed (github.com/MassTransit/MassTransit/releases/tag/v6.0.0) – Courtier

@PylypLebediev I believed that back then it was version 5.5.5. – Bromleigh

Answer 1

It is all described in the documentation.

ConsoleApp1:Program-YourMessage is the message contract exchange, here messages are being published.

test_queue is the endpoint exchange. It binds to the message exchange. This way, when you have multiple consumers for the same message type (pub-sub), they all get their copy of the message.

test_queue is the queue, which binds to the endpoint exchange. Publish-subscribe in RMQ requires exchanges and queues can find to exchanges, so messages get properly delivered.

Both non-durable queue and exchange with weird names are the endpoint temp queue and exchange, which are used for request-response.

Chlori

I can't find that information in the documentation, can I prevent the creation of the non durable queue and exchange? I mean if we don't use the request-response but just regular publishing? Also it is an issue to have the same exchange name for different .NET types? – Bromleigh

I don't think so, but what is exactly the issue with having them? – Chlori

just would like a way either to change their name with something more explicit or to avoid their creation. I mean if we don't use that feature of RabbitMQ, what's the point of having them? – Bromleigh

Name of message queues can be changed by using sbc.OverrideDefaultBusEndpointQueueName("endpoint"); method of IRabbitMqBusFactoryConfigurator – Courtier

The link is broken in the answer, but I cannot edit it because there are too many pending edits. Current link (MassTransit v8): masstransit.io/documentation/configuration/transports/… – Norvell