How would you design the interaction between microservices if a business process consists of several steps and requires data consistency between services?

The following approaches are typically used for designing interactions between microservices in a multi-step business process with data consistency requirements:

1. Orchestration

   • A central service (orchestrator) manages the sequence of microservice calls.
   • The orchestrator tracks the state of each step and makes decisions about continuation or compensation.

2. Choreography

   • Each microservice reacts to events published by other services.
   • There is no central controller; consistency is achieved through event exchange.

3. Using the Saga pattern

   • The transaction is broken into a series of local transactions within each service.
   • Compensating actions are performed in case of errors to rollback changes.
   • Sagas can be implemented via orchestration or choreography.

4. Idempotency and repeatability

   • All operations should be idempotent to safely repeat requests in case of failures.

5. Event-driven architecture

   • Microservices exchange events through message brokers (Kafka, RabbitMQ).
   • Ensures asynchrony and fault tolerance.

6. Monitoring and tracing

   • It is important to have centralized monitoring and tracing (e.g., OpenTelemetry) to track the state of the business process.

Example: for an online store order

• The orchestrator initiates the "Payment Verification" step.
• Upon successful payment, an event "Payment Confirmed" is published.
• The delivery service subscribes to this event and begins preparing for shipment.
• If an error occurs at any step, the orchestrator initiates compensating actions (e.g., refund).

This approach allows ensuring data consistency between microservices without using distributed transactions, which are complex and poorly scalable.