Communication Styles in Microservices
There are two communication styles in distributed systems:
- Direct, a.k.a. synchronous
- Indirect, a.k.a asynchronous
Direct communication is used when a service wants to send a command to another, or when it wants to orchestrate a sequence of behaviors by multiple services, or when it needs to get an immediate response for its request. The upside of using direct communication is that it's easier to do, compared to indirect communication. The downside of direct communication is the tight coupling and the single point of failure. Using REST is an example of direct communication.
On the other hand, indirect communication is used when a service wants to notify one or more services of something, and when an immediate response is not needed. The upside of using this style is the loose coupling and the elimination of the single point of failure we get with direct communication. The downside of it is the added complexity to set up indirect communication. Using a message queue like RabbitMQ is an example of indirect communication.