Is it possible to create a service that consume both message streaming (from Kafka) and also read REST API request, in Go?

I recently read an article Sharing Data Between Microservices on High Scale<br>

There's this image that is about Asynchronous connection. <br>

If I make no mistake, the Order Page service in this picture seems to be able to read messages streaming from Kafka, and also read REST API request from front-end app.<br>

So, I wonder if it's possible to write a service that can do both :

• Read messages streaming from Kafka
• Read REST API request<br>

In just 1 service, for instance in Go.<br>

Also whether is it a good idea ?

Yes, you can definitely write a go service that consumes from Kafka and also exposes a REST endpoint. However, this is not a desirable design decision.

The Kafka-based streaming system allows asynchronous communication between the producer and consumer. However, the REST API-based system does the synchronous communication between the caller and the callee.

The availability guarantee between the sync and sync mode communication is different. The Kafka streaming-based system will have a different availability guarantee than the REST API. In the streaming system, we focus on the throughput of message processing, whereas in the sync communication end-to-end, latency is the main focus (you don't want to keep the caller waiting for a long time to get the result).

If we put both these types of systems in a single service, it becomes difficult to gaze at the availability of the service. Also, the async part or the sync part of the service can play a part in a noisy neighbour for the other side, thus making the service unavailable.

So in general, it is recommended to keep the REST-based API and Kafka streaming as two separate services.

Yes, this is possible. Kafka Streams Interactive Queries covers this exact use case, however, that is all done in JVM Framework, and would need to be ported over to Go.