Microservices asynchronous response

Question

I come across many blog that say using rabbitmq improve the performance of microservices due to asynchronous nature of rabbitmq.

I don't understand in that case how the the http response is send to end user I am elaborating my question below more clearly.

1. user send a http request to microservice1(which is user facing service)

2. microservice1 send it to rabbitmq because it need some service from microservice2

3. microservice2 receive the request process it and send the response to rabbitmq

4. microservice1 receive the response from rabbitmq

NOW how this response is send to browser? Does microservice1 waits untill it receive the response from rabbitmq? If yes then how it become aynchronous??

Answer 1

It's a good question. To answer, you have to imagine the server running one thread at a time. Making a request to a microservice via RestTemplate is a blocking request. The user clicks a button on the web page, which triggers your spring-boot method in microservice1. In that method, you make a request to microservice2, and the microservice1 does a blocking wait for the response.

That thread is busy waiting for microservice2 to complete the request. Threads are not expensive, but on a very busy server, they can be a limiting factor.

RabbitMQ allows microservice1 to queue up a message to microservice2, and then release the thread. Your receive message will be trigger by the system (spring-boot / RabbitMQ) when microservice2 processes the message and provides a response. That thread in the thread pool can be used to process other users' requests in the meantime. When the RabbitMQ response comes, the thread pool uses an unused thread to process the remainder of the request.

Effectively, you're making the server running microservice1 have more threads available more of the time. It only becomes a problem when the server is under heavy load.