Leveraging MassTransit with RabbitMQ for Publisher-Subscriber Messaging in .NET Core

Understanding the Publisher-Subscriber Model

In the pub-sub model, publishers send messages without knowing who will receive them, while subscribers receive messages of interest without knowing who published them. RabbitMQ uses exchanges and queues to implement this model, which works as follows:

1. Publisher: Sends messages to an exchange.
2. Exchange: Routes messages to one or more queues based on specified rules (bindings).
3. Subscriber: Consumes messages from the queue(s).

Step 1: Setting Up RabbitMQ with MassTransit With Docker compose

Run the following command to start RabbitMQ.

Accessing RabbitMQ

• RabbitMQ (API): https://localhost:5672
• RabbitMQ Management UI: https://localhost:15672

docker-compose up -d        

Step 2: Setting Up RabbitMQ with MassTransit

dotnet add package MassTransit
dotnet add package MassTransit.RabbitMQ        

Step 3: . Configure MassTransit with RabbitMQ in Startup.cs

We configure MassTransit to use RabbitMQ as the message broker, setting up the connection and exchange parameters.

Step 4: Define the Message Contract

public interface INotificationMessage
{
    string MessageType { get; }
    string Content { get; }
}        

Step 5: Implement the Consumers

Consumers are classes that receive messages based on their subscriptions.

Step 6: Configure the Consumers

In Startup.cs, add the consumers to the MassTransit configuration. Here, MassTransit will automatically set up topic-based exchanges for each consumer.

Step 7: Publish a message using MassTransit

When you publish a message using MassTransit, it automatically :

• Connects to the RabbitMQ exchange associated with the message type.
• Routes messages to the queues bound to that exchange, based on the defined topic or fanout rules.