Async response from API Gateway in microservices

Question

In microservice architecture, It is suggested that:

1. client app to API gateway communication should be synchronous (like REST over http).

2. API gateway to micro-service communication should also be synchronous

3. But service to service communication should be asynchronous.

Another rule you should try to follow, as much as possible, is to use only asynchronous messaging between the internal services, and to use synchronous communication (such as HTTP) only from the client apps to the front-end services (API Gateways plus the first level of microservices).

https://learn.microsoft.com/en-us/dotnet/standard/microservices-architecture/architect-microservice-container-applications/asynchronous-message-based-communication

Now, If I understood it right, when user requests to API gateway, and in turn it calls the fist service, it will return a acknowledgement (with some GUID) which will be passed to client application. But services will keep on executing the request. Now the question pop ups, how will they notify the client application when the request is processed completely. One way is that client can check the status using the GUID passed to it.

But can it be done with some push notification? How can we integrate server to server push notification?

Answer 1

I have little bit different understanding on this as it says communication between services should be asynchronous while communication to API gateway and API gateway to service should be rest API. so we don't need to do anything as these are simple API calls and pipeline will handle request-response tracking while asynchronous calls between services will increase the throughput of the service.