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


Microservices in Sydney and Melbourne

I'll be speaking at the YOW! conference and teaching a one day microservices workshop in Sydney and Melbourne. 10% discount with JOINMEATYOW18.

Learn more


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: Command Query Responsibility Segregation (CQRS)

Context

You have applied the Microservices architecture pattern and the Database per service pattern. As a result, it is no longer straightforward to implement queries that join data from multiple services. Also, if you have applied the Event sourcing pattern then the data is no longer easily queried.

Problem

How to implement a query that retrieves data from multiple services in a microservice architecture?

Solution

Define a view database, which is a read-only replica that is designed to support that query. The application keeps the replica up to data by subscribing to Domain events published by the service that own the data.

Examples

Resulting context

This pattern has the following benefits:

  • Supports multiple denormalized views that are scalable and performant
  • Improved separation of concerns = simpler command and query models
  • Necessary in an event sourced architecture

This pattern has the following drawbacks:

  • Increased complexity
  • Potential code duplication
  • Replication lag/eventually consistent views

See also

  • Eventuate, which is a platform for developing transactional business applications.

  • My book Microservices patterns describes this pattern in a lot more detail.


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