How is transaction integrity ensured when transitioning from monolith to microservices?

When transitioning from monolithic to microservices architecture, ensuring transaction integrity becomes more complex due to data distribution and the lack of a single ACID mechanism.

Main approaches:

• Sagas — a sequence of local transactions across different services, each with a compensating operation to rollback in case of error. This allows maintaining data consistency without a global transaction.

• Two-Phase Commit (2PC) — a protocol that ensures atomicity of transactions across services, but it is complex to implement and reduces performance, so it is rarely used in microservices.

• Idempotency and retries — services are designed so that operations can be safely repeated, helping to handle temporary failures.

• Use of message brokers and events — for asynchronous communication and state synchronization between services.

Example of a saga:

1. The order service reserves a product.
2. The payment service deducts money.
3. If payment fails, the order service cancels the reservation.

Thus, integrity is achieved through coordination of local transactions and compensatory actions, rather than through global transactions.