Application events
A service command typically needs to update the database and send messages/events. For example, a service that participates in a saga needs to atomically update the database and sends messages/events. Similarly, a service that publishes a domain event must atomically update an aggregate and publish an event. The database update and sending of the message must be atomic in order to avoid data inconsistencies and bugs. However, it is not viable to use a distributed transaction that spans the database and the message broker to atomically update the database and publish messages/events.
How to reliably/atomically update the database and publish messages/events?
A service that uses a relational database inserts messages/events into an outbox table (e.g. MESSAGE
) as part of the local transaction.
An service that uses a NoSQL database appends the messages/events to attribute of the record (e.g. document or item) being updated.
A separate Message Relay process publishes the events inserted into database to a message broker.
This pattern has the following benefits:
This pattern has the following drawbacks:
This pattern also has the following issues:
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.
My virtual bootcamp, distributed data patterns in a microservice architecture, is now open for enrollment!
It covers the key distributed data management patterns including Saga, API Composition, and CQRS.
It consists of video lectures, code labs, and a weekly ask-me-anything video conference repeated in multiple timezones.
The regular price is $395/person but use coupon KRDNZMEW to sign up for $255 (valid until February 28th). There are deeper discounts for buying multiple seats.
Chris offers numerous resources for learning the microservice architecture.
Chris teaches comprehensive workshops, training classes and bootcamps for executives, architects 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.
Delivered in-person and remotely.
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.
Engage Chris to conduct an architectural assessment.
Alternatively, conduct a self-assessment using the Microservices Assessment Platform.
Join the microservices google group
Application architecture patterns
Decomposition
Refactoring to microservicesnew
Data management
Transactional messaging
Testing
Deployment patterns
Cross cutting concerns
Communication style
External API
Service discovery
Reliability
Security
Observability
UI patterns