Tell me about the Saga pattern. How did you implement it? How did you notify services about the rollback?

The Saga pattern is used for managing distributed transactions when multiple services need to perform operations, and in case of an error, already completed steps should be rolled back.

Saga is broken down into a sequence of local transactions with compensating actions (rollbacks). If one of the steps fails, compensating transactions are triggered for the previous steps.

Implementation:

• Orchestration — a central coordinator manages the sequence of steps and rollback.
• Choreography — each service publishes events about execution and listens to other services' events to trigger its own steps.

Rollback notification:

• Through message bus events (e.g., Kafka, RabbitMQ), services receive commands to perform compensating actions.
• In orchestration, the coordinator sends rollback requests to specific services.

Example (simplified):

1. Service A performs an action, publishes an "A completed" event.
2. Service B listens to the event, performs its action, and publishes "B completed".
3. If Service B cannot perform its action, the coordinator initiates a compensating transaction for Service A.

In Python, Saga can be implemented using message queues and step states, for example, using Celery and a message broker.