I'm trying to understand the database per service pattern in microservices architecture.
Say we have a restaurant reservation application composed of the following microservices:
If a user wants to create a reservation, the UI would perform a POST request to /api/reservation with the data in the request body.
Would the Reservation database be required to store redundant data from the User database (user_id, username, first name, last name)?
Or would it only store a user_id reference owned the User database?