Inter-Service Communication

Introduction

Services talk via HTTP, gRPC, or async messaging. Pick by latency, coupling and durability needs.

Understanding the topic

Three options, three trade-offs:

• HTTP/REST — universal, easy to test, synchronous (= caller waits & couples on availability).
• gRPC — binary, fast, schema-first; great for internal high-throughput.
• Async messaging (Kafka, RabbitMQ) — durable, decoupled, eventually consistent. Ideal for events.

Informative example

Modern HTTP client (Spring 6 declarative):

public interface PricingClient {
  @GetExchange("/quotes")
  Quote quote(@RequestParam List<Long> itemIds);
}

@Bean PricingClient pricingClient(WebClient.Builder builder) {
  WebClient wc = builder.baseUrl("http://pricing-service").build();
  HttpServiceProxyFactory factory =
      HttpServiceProxyFactory.builderFor(WebClientAdapter.create(wc)).build();
  return factory.createClient(PricingClient.class);
}