Why did you use both Kafka and gRPC simultaneously? Which scenarios used Kafka, and which used gRPC?

Kafka and gRPC are used together to cover different interaction scenarios between services.

Kafka is a messaging system supporting queues and publish/subscribe. It is well-suited for asynchronous processing, event transmission, and integration between services where reliable delivery and scalability are important. For example, scenarios where a large stream of events needs to be processed, logging, analytics, or when services should not wait for an immediate response.

gRPC is a high-performance remote procedure call (RPC) protocol suitable for synchronous interaction between services with low latency. It is used when an immediate response is needed, such as data retrieval requests, CRUD operations, or when strict API contract enforcement is important.

Thus:

• Kafka handles asynchronous communication scenarios, event processing, and integration with other systems, where reliability and scalability are crucial.
• gRPC handles synchronous requests between services that require quick responses and strict typing.

This separation allows optimizing architecture for different communication requirements.