About Microservices.io

Microservices.io is brought to you by Chris Richardson. Experienced software architect, author of POJOs in Action and the creator of the original CloudFoundry.com. His latest startup is eventuate.io, a microservices application platform.


Microservices consulting and training

Chris offers a comprehensive consulting services, workshops and hands on training classes to help you use microservices effectively.

Avoid the pitfalls of adopting microservices and learn essential topics, such as service decomposition and design and Kubernetes. Find out more


Public workshops in Chicago and Stockholm

In May, I am teaching a couple of public workshops in Chicago and Stockholm, Sweden


Learn more about microservices

Chris offers a comprehensive set of resources for learning about microservices including articles, an O'Reilly training video, and example code.

Learn more


Example microservices applications

Want to see an example? Check out Chris Richardson's example applications. See code


Get the book: Microservice patterns


Signup for the newsletter

A new microservices application platform that solves distributed data management problems.

Join the microservices google group

Pattern: Application publishes events

Also known as

Transaction outbox pattern

Context

A service typically need to atomically update the database and publish messages/events. For example, perhaps it uses the Saga pattern. In order to be reliable, each step of a saga must atomically update the database and publish messages/events. Alternatively, it might use the Domain event pattern, perhaps to implement CQRS. In either case, 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.

Problem

How to reliably/atomically update the database and publish messages/events.

Forces

  • 2PC is not an option

Solution

The application that uses a relational database inserts messages/events into an outbox table (e.g. MESSAGE) as part of the local transaction. An application 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.

Result context

This pattern has the following benefits:

  • High level domain events
  • No 2PC

This pattern has the following drawbacks:

  • Potentially error prone since the developer might forget to publish the message/event after updating the database.

Learn more


Copyright © 2018 Chris Richardson • All rights reserved • Supported by Kong.