Microservice Architecture
Supported by KongPattern: 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 WSSEULWL to sign up for $190 (valid until November 30th, 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
-
My book’s FTGO example application has the
Order History Service, which implements this pattern. -
There are several Eventuate-based example applications that illustrate how to use this pattern.
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
Related patterns
- The Database per Service pattern creates the need for this pattern
- The API Composition pattern is an alternative solution
- The Domain event pattern generates the events
- CQRS is often used with Event sourcing
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.
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 WSSEULWL to sign up for $190 (valid until November 30th, 2022). There are deeper discounts for buying multiple seats.
LEARN about microservices
Chris offers numerous resources for learning the microservice architecture.
Training classes
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.
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Example microservices applications
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Consulting services
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The Eventuate platform
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.
ASSESS your architecture
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Engage Chris to conduct an architectural assessment.
Self assessment
Alternatively, conduct a self-assessment using the Microservices Assessment Platform.
Join the microservices google group
The patterns
Application architecture patterns
Decomposition
- Decompose by business capability
- Decompose by subdomain
- Self-contained Servicenew
- Service per teamnew
Refactoring to microservicesnew
Data management
Transactional messaging
Testing
Deployment patterns
- Multiple service instances per host
- Service instance per host
- Service instance per VM
- Service instance per Container
- Serverless deployment
- Service deployment platform
Cross cutting concerns
Communication style
External API
Service discovery
- Client-side discovery
- Server-side discovery
- Service registry
- Self registration
- 3rd party registration
Reliability
Security
Observability
- Log aggregation
- Application metrics
- Audit logging
- Distributed tracing
- Exception tracking
- Health check API
- Log deployments and changes
UI patterns