Fundamentals of Software Architecture

This difference between internal class-level orchestration and external service orchestration points to one of the many significant differences between service-based architecture and microservices in terms of granularity. Because domain services are coarse-grained, regular ACID (atomicity, consistency, isolation, durability) database transactions involving database commits and rollbacks are used to ensure database integrity within a single domain service. Highly distributed architectures like microservices, on the other hand, usually have fine-grained services and use a distributed transaction technique known as BASE transactions (basic availability, soft state, eventual consistency) that rely on eventual consistency and hence do not support the same level of database integrity as ACID transactions in a service-based architecture. To illustrate this point, consider the example of a catalog checkout process within a service-based architecture. Suppose the customer places an order and the credit card used for payment has expired. Since this is an atomic transaction within the same service, everything added to the database can be removed using a rollback and a notice sent to the customer stating that the payment cannot be applied. Now consider this same process in a microservices architecture with smaller fine-grained services. First, the OrderPlacement service would accept the request, create the order, generate an order ID, and insert the order into the order tables. Once this is done, the order service would then make a remote call to the PaymentService, which would try to apply the payment. If the payment cannot be applied due to an expired credit card, then the order cannot be placed and the data is in an inconsistent state (the order information has already been inserted but has not been approved). In this case, what about the inventory for that order? Should it be marked as ordered and decremented?