# Getting Started

Getting started with MassTransit is fast and easy. This quick start guide uses RabbitMQ with .NET Core. RabbitMQ must be installed, instructions for installing RabbitMQ are included below.

The .NET Core SDK should be installed before continuing.

To create a service using MassTransit, create a console application via the Command Prompt.

$ mkdir GettingStarted
$ dotnet new console -o GettingStarted

Add some references to the newly created console application:

$ cd GettingStarted
$ dotnet add package MassTransit.RabbitMQ

At this point, the project should compile, but there is more work to be done. You can verify the project builds by executing:

$ dotnet run

If you have any errors at this point, you might want to get them resolved.

# Edit Program.cs

You can view a working project on GitHub. There are other samples available as well.

To get started, a bare bones Program.cs is shown below.

public class Message
{ 
    public string Text { get; set; }
}

public class Program
{
    public static async Task Main()
    {
        var bus = Bus.Factory.CreateUsingRabbitMq(sbc =>
        {
            sbc.Host("rabbitmq://localhost");

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

        await bus.StartAsync(); // This is important!

        await bus.Publish(new Message{Text = "Hi"});
        
        Console.WriteLine("Press any key to exit");
        await Task.Run(() => Console.ReadKey());
        
        await bus.StopAsync();
    }
}

Save the file, and execute dotnet run, and you should see the message Received: Hi displayed. If you see anything else, something went wrong. Verify your RabbitMQ installation and your .NET Core setup, basically all the things that could possibly go wrong you should fix.

# Install RabbitMQ

TIP

If you are using a Mac, RabbitMQ can be installed using Homebrew by typing brew install rabbitmq. This installs the management plug-in automatically.

# To install RabbitMQ manually:

Install Erlang using the installer. (Next -> Next ...)
Install RabbitMQ using the installer. (Next -> Next ...) You now have a RabbitMQ broker (look in services.msc for it) that you can log into using guest, guest. You can see message rates, routings and active consumers using this interface.

First, from an elevated command prompt, change directory to the sbin folder within the RabbitMQ Server installation directory e.g. %PROGRAMFILES%\RabbitMQ Server\rabbitmq_server_3.5.3\sbin\
Next, run the following command to enable the rabbitmq management plugin: rabbitmq-plugins.bat enable rabbitmq_management

# What is this doing?

If we are going to create a messaging system, we need to create a message. Message is a .NET class that will represent our message. Notice that it's just a Plain Old CLR Object (or POCO).

Next up, we need a program to run our code. Here we have a standard issue command line Main method. To setup the bus we start with the static class Bus and work off of the Factory extension point. From there we call the CreateUsingRabbitMQ method to setup a RabbitMQ bus instance. This method takes a lambda whose first and only argument is a class that will let you configure every aspect of the bus.

One of your first decisions is going to be "What transport do I want to run on?" Here we have chosen RabbitMQ (Bus.Factory.CreateUsingRabbitMQ()) because its the defacto transport choice for MassTransit.

After that we need to configure the RabbitMQ host settings sbc.Host(). The first argument sets the machine name and the virtual directory to connect to. After that you have a lambda that you can use to tweak any of the other settings that you want. Since no additional configuration is specified, the default username and password (guest/guest) is being used.

Now that we have a host to listen on, we can configure some receiving endpoints sbc.ReceiveEndpoint. We specifiy the queue we want to listen on and a lambda to register each handler that we want to use.

Lastly, in the configuration, we have the Handler<Message> method which subscribes a handler for the message type Message and takes an async lambda (oh yeah baby TPL) that is given a context class to process. Here we access the message by traversing context.Message and then writing to the console the text of the message.

And now we have a bus instance that is fully configured and can start processing messages. We can grab the busControl that we created and call StartAsync on it to get everything rolling. We again await on the result and now we can go.

IMPORTANT

You must start the bus, otherwise you will get issues with sending and receiving messages. There is no "send-only" bus with MassTransit.