How to communicate from REST to message queue

Question

how is that possible that a REST Microservice can communicate with another Microservice which is a hybrid, which means he can communicate with REST and with a Message Queue. For Example an API-Gateway. For the outside world, he is able to communicate with an App, Mobilephone via REST but the communication from the backend is via message queue.

Use case:

My homepage wants to get a Vehicle from the database. He asks the API-Gateway via a GET-Request. The API-Gateway takes the GET-request and publishes it into the message queue. The other Microservice takes the message and publishes the result. Then the API-gateway consumed the result and send it back as a response.

How can I implement it? Am I using Spring boot with Apache Kafka? Do I need to implement an asynchronous communication?

(Sorry its german)

Answer 1

There are some approaches to solve this situation.

You might create topics for each client request and wait for the reply on the other side, e.g, DriverService would read the request message, fetch all your data and publish it to your client request topic. As soon as you consume the response message, you destroy that topic.

BUT 'temporary' topics might take too long to be delete(if no configuration avoids that, such as delete.topic.enable property) in a request-response interaction, and you need to monitor possible topics overgrowth.

Websocket is another possible solution. Your client would start listening to a specific topic, previously agreed with your server, then in a specific timeout you would wait for the response, when your DriverService would publish to that specific socket channel.

Spring Boot offers you great starters for Kafka and Websockets. If you are expecting a large amount of transactions, I would go with a mixed strategy, using Kafka to help my backend scale and process all transactions, then would respond to client via Websocket.