We can identify different styles of communication between microservices. It is possible to classify them into two dimensions. The first of them is a division into synchronous and asynchronous communication protocols. The key point of asynchronous communication is that the client should not have blocked a thread while waiting for a response. The most popular protocol for that type of communication is AMQP, and we already had the opportunity to run an example of that protocol usage at the end of the previous chapter. However, the main way of communication between services is still synchronous HTTP protocol. We will be only talking about it in this chapter.
The second division is into different communication types based on whether there is a single message receiver or multiple receivers. In one-to-one communication, each request is processed by exactly one service instance. In one-to-many communication, each request may be processed by many different services...