Automating MassTransit Consumer Registration

When working with MassTransit, registering consumers can become cumbersome if you have many of them. Luckily, MassTransit provides a way to register all your consumers automatically using AddConsumers. This post will guide you through the process of setting up and using AddConsumers to simplify your consumer registration.

What is MassTransit?

MassTransit is an open-source distributed application framework for .NET, which simplifies the creation and management of message-based systems. It supports various messaging platforms like RabbitMQ, Azure Service Bus, and Amazon SQS.

Setting Up MassTransit

Before diving into consumer registration, let’s quickly set up a MassTransit project.

Step 1: Install MassTransit Packages

First, install the necessary MassTransit packages via NuGet. You can use the following command on your favorite command line:

dotnet add package MassTransit.RabbitMQ

Step 2: Configure MassTransit

In your Program.cs or wherever you configure your services, set up MassTransit:

	public class Program
	{
	public static void Main(string[] args)
	{
	CreateHostBuilder(args).Build().Run();
	}
	public static IHostBuilder CreateHostBuilder(string[] args) =>
	Host.CreateDefaultBuilder(args)
	.ConfigureServices((hostContext, services) =>
	{
	services.AddMassTransit(x =>
	{
	x.UsingRabbitMq((context,cfg) =>
	{
	cfg.ConfigureEndpoints(context);
	});
	});
	});
	}

view raw Program.cs hosted with ❤ by GitHub

Registering Consumers Automatically

Manually registering each consumer can be tedious, especially in a large application. MassTransit provides the AddConsumers method, which scans and registers all consumers in your assembly.

Step 1: Create Your Consumers

First, let’s create a few consumers:

	public class OrderSubmittedConsumer : IConsumer<OrderSubmitted>
	{
	public Task Consume(ConsumeContext<OrderSubmitted> context)
	{
	// Handle the message
	return Task.CompletedTask;
	}
	}
	public class PaymentProcessedConsumer : IConsumer<PaymentProcessed>
	{
	public Task Consume(ConsumeContext<PaymentProcessed> context)
	{
	// Handle the message
	return Task.CompletedTask;
	}
	}

view raw Consumers.cs hosted with ❤ by GitHub

When registering consumers automatically, I recommend to add a consumer definition for each consumer. This allows us to specify the configuration applicable for every consumer:

	public class OrderSubmittedConsumerDefinition :
	ConsumerDefinition<OrderSubmittedConsumer>
	{
	public OrderSubmittedConsumerDefinition()
	{
	EndpointName = "submitted-orders";
	ConcurrentMessageLimit = 4;
	}
	protected override void ConfigureConsumer(IReceiveEndpointConfigurator endpointConfigurator,
	IConsumerConfigurator<OrderSubmittedConsumer> consumerConfigurator)
	{
	endpointConfigurator.UseMessageRetry(r => r.Interval(5, 1000));
	endpointConfigurator.UseInMemoryOutbox();
	}
	}
	public class PaymentProcessedConsumerDefinition :
	ConsumerDefinition<PaymentProcessedConsumer>
	{
	public PaymentProcessedConsumerDefinition()
	{
	EndpointName = "processed-payments";
	ConcurrentMessageLimit = 4;
	}
	protected override void ConfigureConsumer(IReceiveEndpointConfigurator endpointConfigurator,
	IConsumerConfigurator<PaymentProcessedConsumer> consumerConfigurator)
	{
	endpointConfigurator.UseMessageRetry(r => r.Interval(5, 1000));
	endpointConfigurator.UseInMemoryOutbox();
	}
	}

view raw ConsumerDefinitions.cs hosted with ❤ by GitHub

Step 2: Register Consumers Automatically

Modify your MassTransit configuration to use AddConsumers:

	public class Program
	{
	public static void Main(string[] args)
	{
	CreateHostBuilder(args).Build().Run();
	}
	public static IHostBuilder CreateHostBuilder(string[] args) =>
	Host.CreateDefaultBuilder(args)
	.ConfigureServices((hostContext, services) =>
	{
	services.AddMassTransit(x =>
	{
	// Automatically registers all consumers and consumerdefinitions in the current assembly
	x.AddConsumers(typeof(Program).Assembly);
	x.UsingRabbitMq((context,cfg) =>
	{
	cfg.ConfigureEndpoints(context);
	});
	});
	});
	}

view raw Program.cs hosted with ❤ by GitHub

AddConsumers will scan the specified assembly (in this case, the assembly containing the Program class) and registers all implementations of IConsumer it finds. It will also search for related ConsumerDefinition<T> implementations and load them as well.

By using this method MassTransit will automatically detect and configure the consumers, significantly reducing the boilerplate code required for consumer registration.

More information

Consumers · MassTransit