Microservice internal communication

Question

I've been reading up on Microservice Architecture But I still can't understand the inter-microservices communication mechanism.
In many articles they said that microservices are usually exposed over a RESTful API. But when you search the internet you always see implementations based on messaging and events for the backend communications.

So I'm confused, Is REST API a standard for all the microservices or we can see microservices without a REST endpoints.

Answer 1

For your problem , first lets understand the ways in which one service interacts with each other , lets create two service order service and customer service :

1. One service need some data from other service to process its requests, eg: lets say you want to place an order , so from ui you must hit http request to order service (which can be rest , or have a api gateway in between n that use some other protocol like protobu ) to call order service for placing an order , now assume order service needs to check the validity of the customer , so order service needs to call customer service in sync — most probably you will hit rest or create a protobuf or have a persistent websocket between the service and then after response from customer service , order service move ahead.

In this case sync communication needs to be imitated , one direct approach is rest or protobuff , or imitate it through messaging

2. Based on one service events , you want to update other service : in this generally the preferred style is messaging bus , where one service emits out event and multiple other services have a listener on the messaging bus and react accordingly . Eg : lets say on update of customer name in customer service , you want to update the cached name of the customer in order service , in this when name is updated in customer service , it emits customer name updated event , order service subscribe to it , then react to it

Your third question is , is it possible to have service with no rest endpoint ::: yes its possible , but every service needs to be reachable . So use rest or other form is needed

Above mentioned link : microservices.io is very good , go through it once again