MassTransit–Change Exchange naming strategy

When you publish a message through MassTransit to RabbitMQ, a default naming strategy is used to create a corresponding exchange. The default naming convention is the fully qualified name of the message class, so if you have a class named HelloWorldMessage in a namespace MyCompany.Messages.V1, you’ll end up with an exchange named MyCompany.Messages.V1:HelloWorldMessage.

This is ok if you are running RabbitMQ locally(through Docker for example), but it gets quite annoying if you are publishing to a shared infrastructure during development. The problem is that you start receiving messages from other developers which makes debugging a lot more difficult.

To solve this problem I created a custom EntityNameFormatter that allows you to specify an extra environment setting that can be set to for example to a specific username. Doing this in MassTransit 5 is not that hard as you can set this for the whole MessageTopology(something that was not easily done in previous versions).

Here is the required code:

• First, we have to create a custom formatter by implementing the IEntityFormatter interface(note that I’m passing in the original formatter):

	class EnvironmentNameFormatter : IEntityNameFormatter
	{
	private IEntityNameFormatter _original;
	public EnvironmentNameFormatter(IEntityNameFormatter original)
	{
	_original = original;
	}
	public string FormatEntityName<T>()
	{
	var environment = ConfigurationManager.AppSettings["Environment"];
	return $"{environment}:{_original.FormatEntityName<T>()}";
	}
	}

view raw EnvironmentNameFormatter.cs hosted with ❤ by GitHub

• Second, we have to apply this formatter. As I want to do this for all messages, I specify it on the MessageTopology setting:

	var bus = Bus.Factory.CreateUsingRabbitMq(sbc =>
	{
	var host = sbc.Host(new Uri("rabbitmq://demo:5672"), h =>
	{
	h.Username("demo");
	h.Password("demo");
	});
	sbc.MessageTopology.SetEntityNameFormatter(new EnvironmentNameFormatter(sbc.MessageTopology.EntityNameFormatter));
	});

view raw MassTransitConfig.cs hosted with ❤ by GitHub

Now we can specify a different name in our configuration and only receive the messages that we want.

Remark: You have to apply this code both on the send and receive side of your application