Microservice and RabbitMQ

Question

I am new to Microservices and have a question with RabbitMQ / EasyNetQ. I am sending messages from one microservice to another microservice.

Each Microservice are Web API's. I am using CQRS where my Command Handler would consume message off the Queue and do some business logic. In order to call the handler, it will need to make a request to the API method.

I would like to know without having to explicit call the API endpoint to hit the code for consuming messages. Is there an automated way of doing it without having to call the API endpoint ?

Suggestion could be creating a separate solution which would be a Console App that will execute the RabbitMQ in order to start listening. Create a while loop to read messages, then call the web api endpoint to handle business logic every time a new message is sent to the queue.

My aim is to create a listener or a startup task where once messages are in the queue it will automatically pick it up from the Queue and continue with command handler but not sure how to do the "Automatic" way as i describe it. I was thinking to utilise Azure Webjob that will continuously be running and it will act as the Consumer.
Looking for a good architectural way of doing it.

Programming language being used is C#

Much Appreciated

Answer 1

The recommended way of hosting RabbitMQ subscriber is by writing a windows service using something like topshelf library and subscribe to bus events inside that service on its start. We did that in multiple projects with no issues.

If you are using Azure, the best place to host RabbitMQ subscriber is in a "Worker Role".

Answer 2

I think using the CQRS pattern, you will have events as well and corresponding event handlers. As you are using RabbitMQ for asynchronous communication between command and query then any message put on specific channel on RabbitMQ, can be listened by a callback method

Receiving messages from the queue is more complex. It works by subscribing a callback function to a queue. Whenever we receive a message, this callback function is called by the Pika library.

Answer 3

I am using CQRS where my Command Handler would consume message off the Queue and do some business logic. In order to call the handler, it will need to make a request to the API method.

Are you sure this is real CQRS? CQRS occures when you handle queries and commands differently in your domain logic. Receiving a message via a calss, that's called CommandHandler and just reacting to it is not yet CQRS.

My aim is to create a listener or a startup task where once messages are in the queue it will automatically pick it up from the Queue and continue with command handler but not sure how to do the "Automatic" way as i describe it. I was thinking to utilise Azure Webjob that will continuously be running and it will act as the Consumer. Looking for a good architectural way of doing it.

The easier you do that, the better. Don't go searching for complex solutions until you tried out all the simple ones. When I was implementing something similar, I was just running a pool of message handler scripts using Linux cron. A handler poped a message off the queue, processed it and terminated. Simple.