How do microservices communicate?

Synchronous Communication

HTTP Requests

Microservices communicate with each other using HTTP requests. Each microservice has its own REST API. In Spring Boot, we can use the RestTemplate class to make HTTP requests.

Eureka and Feign

Eureka is a service registration tool. It allows microservices to register themselves and discover other services. Each service send a heartbeat to Eureka to let it know that it is still alive. If Eureka does not receive a heartbeat from a service, it will remove it from its registry.

Feign is a REST client to make HTTP requests to other microservices without using RestTemplate. It uses Eureka to discover other services. In this way, we can make HTTP requests to other services without hardcoding the URL, also simplifying the code.

Asynchronous Communication

Message Brokers

We can use a message broker like RabbitMQ or Kafka to send messages between microservices to communicate Asychonously.

For example, when a user creates a new account, we can send a message to the email service to send a welcome email and to the notification service to send a notification to the user