A service command typically needs to create/update/delete aggregates in the database and send messages/events to a message broker. For example, a service that participates in a saga needs to update business entities and send messages/events. Similarly, a service that publishes a domain event must update an aggregate and publish an event.
The command must atomically update the database and send messages in order to avoid data inconsistencies and bugs. However, it is not viable to use a traditional distributed transaction (2PC) that spans the database and the message broker The database and/or the message broker might not support 2PC. And even if they do, it’s often undesirable to couple the service to both the database and the message broker.
But without using 2PC, sending a message in the middle of a transaction is not reliable. There’s no guarantee that the transaction will commit. Similarly, if a service sends a message after committing the transaction there’s no guarantee that it won’t crash before sending the message.
In addition, messages must be sent to the message broker in the order they were sent by the service.
They must usually be delivered to each consumer in the same order although that’s outside the scope of this pattern.
For example, let’s suppose that an aggregate is updated by a series of transactions T1
, T2
, etc.
This transactions might be performed by the same service instance or by different service instances.
Each transaction publishes a corresponding event: T1 -> E1
, T2 -> E2
, etc.
Since T1
precedes T2
, event E1
must be published before E2
.
How to atomically update the database and send messages to a message broker?
One or more database triggers insert events into an EVENTS
table, which is polled by a separate process that publishes the events.
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 workshops.
Chris teaches comprehensive workshops for architects and developers that will enable 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.
Learn moreChris offers numerous other resources for learning the microservice architecture.
Want to see an example? Check out Chris Richardson's example applications. See code
Got a specific microservice architecture-related question? For example:
Consider signing up for a two hour, highly focussed, consulting session.
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 RESVJCMC to sign up for $95 (valid until September 26th, 2023). There are deeper discounts for buying multiple seats.
Take a look at my Manning LiveProject that teaches you how to develop a service template and microservice chassis.
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.
Note: tagging is work-in-process
Microservices adoption · ancient lore · anti-patterns · application api · application architecture · architecting · architecture · architecture documentation · assemblage · beer · containers · dark energy and dark matter · deployment · design-time coupling · developer experience · development · devops · docker · eventuate platform · glossary · hexagonal architecture · implementing commands · implementing queries · inter-service communication · kubernetes · loose coupling · microservice architecture · microservice chassis · microservices adoption · microservicesio updates · modular monolith · multi-architecture docker images · observability · pattern · refactoring to microservices · resilience · sagas · security · service api · service architecture · service collaboration · service design · service discovery · service granularity · service template · software delivery metrics · success triangle · tacos · team topologies · transaction management · transactional messaging
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