Microservices Pattern: Saga

Implement each business transaction that spans multiple services as a saga. A saga is a sequence of local transactions. Each local transaction updates the database and publishes a message or event to trigger the next local transaction in the saga. If a local transaction fails because it violates a business rule then the saga executes a series of compensating transactions that undo the changes that were made by the preceding local transactions.

There are two ways of coordination sagas:

• Choreography - each local transaction publishes domain events that trigger local transactions in other services
• Orchestration - an orchestrator (object) tells the participants what local transactions to execute

In order to be reliable, a service must atomically update its database and publish a message/event. It cannot use the traditional mechanism of a distributed transaction that spans the database and the message broker.

The following patterns are ways to atomically update state and publish messages/events:

• Event sourcing
• Transactional Outbox