Publish to Azure Service Bus using MassTransit is causing errors

Question

I am new to both MassTransit and Azure Service Bus. I am attempting to use an architecture where either RabbitMq or Azure Service Bus is used in a .NET Core 3.1 API.I have the RabbitMq portion working and just started on the Azure Service Bus. I have an API that will take an incoming payload and publish it to a queue. When I attempt to publish via the Azure Service Bus approach, I get an error "SubCode=40000. Cannot operate on type Topic because the namespace 'servicehubqa' is using 'Basic' tier.

I am attempting to use a queue approach and am hoping to create the queue as messages are published. Currently, the service bus is using a Basic pricing tier as the documentation says that I can play with queues at that level. I am not sure if I need to manually create the queue (I had to do this approach using RabbitMq since no queue would be created if no consumer exists). Is topic the default approach if nothing is specified? How do I specify queue vs topic?

My code is as follows below.

Startup - ConfigureServices

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddSingleton(Configuration);

        services.AddScoped<IMassTransitRabbitMqTransport, MassTransitRabbitMqTransport>();
        services.AddScoped<IMassTransitAzureServiceBusTransport, MassTransitAzureServiceBusTransport>();

        var messageProvider = ConfigProvider.GetConfig("MessageService", "Messaging_Service");
        switch (messageProvider)
        {
            case "AzureServiceBus":
                services.AddScoped<IMessagingService, MassTransitAzureServiceBusMessagingService>();
                break;
            case "RabbitMq":
                services.AddScoped<IMessagingService, MassTransitRabbitMqMessagingService>();
                break;
            default:
                throw new ArgumentException("Invalid message service");
        };

        services.AddControllers();
    }

Controller

public class ListenerController : ControllerBase
{
    readonly ILogger<ListenerController> logger;
    readonly IMessagingService messenger;

    public ListenerController(
        ILogger<ListenerController> logger,
        IMessagingService messenger)
    {
        this.logger = logger;
        this.messenger = messenger;
    }

    [HttpPost]
    public async Task<IActionResult> Post()
    {
        var payload = new
        {
            ...
        };

        await messenger.Publish(payload);

        return Ok();
    }
}

IMessagingService

public interface IMessagingService
{
    Task Publish(object payload);
}

IMassTransitTransport

public interface IMassTransitTransport
{
    IBusControl BusControl { get; }
}

public interface IMassTransitRabbitMqTransport : IMassTransitTransport { }

public interface IMassTransitAzureServiceBusTransport : IMassTransitTransport { }

MassTransitAzureServiceBusTransport

public sealed class MassTransitAzureServiceBusTransport : IMassTransitAzureServiceBusTransport
{
    public IBusControl BusControl { get; }

    public MassTransitAzureServiceBusTransport()
    {
        BusControl = ConfigureBus();
        BusControl.StartAsync();
    }

    IBusControl ConfigureBus()
    {
        return Bus.Factory.CreateUsingAzureServiceBus(config => {
            var host = config.Host(ConfigProvider.GetConfig("AzureServiceBus", "AzureServiceBus_ConnStr"), host => { });
        });
    }
}

MassTransitAzureServiceBusMessagingService

public class MassTransitAzureServiceBusMessagingService : IMessagingService
{
    readonly IMassTransitAzureServiceBusTransport massTransitTransport;

    public MassTransitAzureServiceBusMessagingService(IMassTransitAzureServiceBusTransport massTransitTransport)
    {
        //transport bus config already happens in massTransitTransport constructor
        this.massTransitTransport = massTransitTransport;
    }

    public async Task Publish(object payload)
    {
        var jsn = Newtonsoft.Json.JsonConvert.SerializeObject(payload);
        var cmd = JObject.Parse(jsn)["Command"];

        switch (cmd.ToString())
        {
            case "UPDATESTATUS":
                //IRegisterCommandUpdateStatus is an interface specifying the properties needed
                await massTransitTransport.BusControl.Publish<IRegisterCommandUpdateStatus>(payload);
                break;
            default: break;
        }
    }
}

Answer 1

The Azure Service Bus basic tier does not allow the use of topics. So you would not be able to use publish. That said, MassTransit doesn't really work with the basic tier, despite attempts in the past that may have been successful.

Answer 2

The MassTransit documentation does state that if you want to use a Topic (ie the ability to publish to multiple subscriptions at the same time), you use the publish. If you want to send a message to a queue (the message is routed to a specific location), you use the send and provide the correct information.

Topics require standard pricing and Queues can use basic pricing.

With this information, the MassTransitAzureServiceBusMessagingService would be modified as follows:

Basic Pricing - Queues

    public async Task Publish(object payload)
    {
        var jsn = Newtonsoft.Json.JsonConvert.SerializeObject(payload);
        var cmd = JObject.Parse(jsn)["Command"];

        switch (cmd.ToString())
        {
            case "UPDATESTATUS":
                var queueUri = new Uri(massTransitTransport.BusControl.Address, "registration.updatestatus");
                var endpoint = await massTransitTransport.BusControl.GetSendEndpoint(queueUri);
                await endpoint.Send<IRegisterCommandUpdateStatus>(payload);
                break;
            default: break;
        }
    }

Standard Pricing - Topics/Subscriptions

    public async Task Publish(object payload)
    {
        var jsn = Newtonsoft.Json.JsonConvert.SerializeObject(payload);
        var cmd = JObject.Parse(jsn)["Command"];

        switch (cmd.ToString())
        {
            case "UPDATESTATUS":
                await massTransitTransport.BusControl.Publish<IRegisterCommandUpdateStatus>(payload);
                break;
            default: break;
        }
    }