You have applied the Database per Service pattern. Each service has its own database. Some business transactions, however, span multiple service so you need a mechanism to ensure data consistency across services. For example, lets imagine that you are building an e-commerce store where customers have a credit limit. The application must ensure that a new order will not exceed the customer’s credit limit. Since Orders and Customers are in different databases the application cannot simply use a local ACID transaction.
How to maintain data consistency across services?
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:
An e-commerce application that uses this approach would create an order using a choreography-based saga that consists of the following steps:
Order Servicereceives the
POST /ordersrequest and creates an
Customer Service’s event handler attempts to reserve credit
OrderService’s event handler either approves or rejects the
An e-commerce application that uses this approach would create an order using an orchestration-based saga that consists of the following steps:
Order Servicereceives the
POST /ordersrequest and creates the
Create Ordersaga orchestrator
Reserve Creditcommand to the
Customer Serviceattempts to reserve credit
This pattern has the following benefits:
This solution has the following drawbacks:
There are also the following issues to address:
The following examples implement the customers and orders example in different ways:
Order Serviceuses a saga orchestrator implemented using the Eventuate Tram Sagas framework
Microservices.io is brought to you by Chris Richardson. Experienced software architect, author of POJOs in Action, the creator of the original CloudFoundry.com, and the author of Microservices patterns.
Chris helps clients around the world adopt the microservice architecture through consulting engagements, and training classes and workshops.
Chris offers numerous resources for learning the microservice architecture.
Chris teaches comprehensive workshops and training classes for executives, architectures and developers to help your organization use microservices effectively.
Avoid the pitfalls of adopting microservices and learn essential topics, such as service decomposition and design and how to refactor a monolith to microservices.
Want to see an example? Check out Chris Richardson's example applications. See code
Engage Chris to create a microservices adoption roadmap and help you define your microservice architecture,
Use the Eventuate.io platform to tackle distributed data management challenges in your microservices architecture.
Eventuate is Chris's latest startup. It makes it easy to use the Saga pattern to manage transactions and the CQRS pattern to implement queries.
Join the microservices google group
Application architecture patterns
Cross cutting concerns