How can microservices communicate with each other? REST vs Kafka — criteria for choosing.

Microservices can communicate with each other mainly in two ways: via REST API and through message exchange systems like Kafka.

REST is a synchronous protocol over HTTP, where services exchange requests and responses. Suitable for:

• Requests expecting immediate responses.
• Simple scenarios with low latency.
• When simplicity and transparency of interaction are important.

Kafka is an asynchronous message exchange system (event streaming), where services publish and subscribe to events. Suitable for:

• High-load systems with a large number of messages.
• Scenarios where fault tolerance and scalability are important.
• Event processing and integration of multiple services without tight coupling.

Criteria for choosing:

• If you need a quick response and simplicity — REST.
• If reliability, scalability, and asynchrony are important — Kafka.
• For complex business processes with many events and integrations, Kafka is preferable.

Example: an authorization service can use REST to verify a user, while an analytics service can use Kafka to collect activity events.