I've a question related to microservices world. Let's assume I've two microservices, microservice A does a request to microservice B. Microservice B perform some "long" operations and makes a request to another microservice C. In result microservice A waits for result from microservice B. How to handle such a long operation if the microservice A is "connected" to front end service, where user initiates the operation and waits for the result of that operation.
Is there any good way to handle long-running tasks in those microservices? What would you suggest to me with that case to be the most efficient and scalable in Spring boot? Thank you in advance.
On a high-level, let's segregate the API calls in two major types
Synchronous
This is an ideal situation implemented using RestTemplate, WebClient , FeignClient etc where in your Microservice A would wait for response from Microservice B.
Ideal for quick operations and covers majority use case
Asynchronous
As @taleodor mentioned, the other way would be to implement an async call to other Microservice, which would only return a Run id or Acknowledgement id to indicate the long running process started. To get status of that process, you may think of implementing it through a Message queue such as ActiveMQ or Apache Kafka which works on the concept of producer/consumer or Publisher/subscriber (pub/sub) where in your long running microservice will publish the event once completed, and Microservice A or B will subscribe to that event and read the response !
Apart of message queues, your Microservice A can also implement a scheduled task to check for progress completion or resource updation based on how to implement it !