Pattern: Command Query Responsibility Segregation (CQRS)

Want to learn more about this pattern?

Take a look at my self-paced, online bootcamp that teaches you how to use the Saga, API Composition, and CQRS patterns to design operations that span multiple services.

The regular price is $395/person but use coupon ODVKLZON to sign up for $195 (valid until August 9th, 2022)

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.

Learn more

  • My book Microservices patterns describes this pattern in a lot more detail
  • Take a look at my self-paced, online bootcamp that teaches you how to use the Saga, API Composition, and CQRS patterns to design operations that span multiple services.

About Microservices.io

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.

Brand new public workshop in Australia/APAC timezone

In August, I’ll be teaching a brand new public microservices workshop over Zoom in an APAC-friendly (GMT+9) timezone.

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Learn how to create a service template and microservice chassis

Take a look at my Manning LiveProject that teaches you how to develop a service template and microservice chassis.

New virtual bootcamp: Distributed data patterns in a microservice architecture

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 ODVKLZON to sign up for $195 (valid until August 9th, 2022). There are deeper discounts for buying multiple seats.

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