Overview of Service Communication: Synchronous, Asynchronous, RPC, REST, Service Discovery, and Messaging

Overview

Internal service communication can be divided into two categories: request/response (e.g., REST, gRPC) and asynchronous messaging (e.g., AMQP, STOMP).

Communication Types

Two dimensions: 1‑to‑1 vs 1‑to‑many, and synchronous vs asynchronous.

1‑to‑1 implementations

Request/response communication

Asynchronous request/response

One‑way notification

1‑to‑many implementations

Publish/subscribe

Publish/async response

Message Formats

Messages are either text (JSON, XML) or binary (Avro, Protobuf, Thrift). Language‑agnostic formats are preferred over Java serialization.

RPC

Remote Procedure Call allows a client to invoke a remote service as if it were a local method. The provider’s proxy sends data over the network, the server processes the request, and the result is returned to the client.

REST

REST is a set of architectural constraints, typically using HTTP. Resources represent business entities such as users or orders. Common HTTP methods include POST /user (create), PUT /user (update), GET /users (list), and GET /user/{id} (retrieve).

Service Discovery

Two approaches: static discovery (fixed addresses) and dynamic discovery (service registry or platforms like Kubernetes). Dynamic discovery involves service registration and retrieval from a registry.

Asynchronous Messaging

Message‑oriented applications use a message broker as an intermediary. A sender publishes messages to a channel, and consumers read from the channel. Messages consist of a header (key‑value pairs, including a unique ID) and a body. Types include Document, Command, and Event.

Channels

Channels enable message exchange and come in two forms: point‑to‑point and publish/subscribe.

Implementation Considerations for Asynchronous Messaging

When selecting a message‑queue component, consider supported programming languages, message standards, ordering guarantees, delivery mechanisms, persistence, scalability, and timeliness.