3 Side notes JAX London 2016

Overview

Session link 11th Oct — 10:00 to 10:50 Developing microservices with aggregates By Chirs Richardson

Notes

• Jax Center articles about this session:
  • Developing applications with a micro-service architecture
  • Domain-driven Design and micro-services
• The service boundary enforces modularization:

“2 phase commit is not an option in Micro-service solutions.”

• An aggregate of micro-services is a cluster of objects treated like a unit.
  • An Aggregate has a root service and it is treated like one module of the domain model.
• Aggregate rules:
  • Reference other aggregates via identity (primary key), instead of via object reference.
  • One command by one aggregate. One transaction is contained within a service/aggregate.
  • Atomic actions happen inside one aggregate/service.
• Consistency across aggregates is achieved via an Event Driven Architecture:
  • Publish events when things happen.
  • The events trigger the next step.
  • Multi-step workflows.
• Event sourcing is event-centric persistence:
  • Events become the first class citizens.
  • Store events in persistence layer as a long history.
  • Fold / Reduce the list of events to get the current state.
  • Command Query Responsibility Segregation (CQRS) used to maintain views for querying.
  • Audit log by definition of the solution.
• Event store solution http://eventuate.io/
  • Documentation on event sourcing and Micro-services
  • Documented examples here.
• Micro-services are not easy! It is fervently advised to review all the drawbacks of this new concept:
  • Required to rewrite the application.
  • Required considerable learning curve.
  • Events evolve and change business requirements. Then a version system to work with legacy events will be required.
  • Querying is challenging because it is required to maintain views for each kind of query by using CQRS.

That was all for this session.

Many thanks for reading, please leave a comment if you have any quality hint.

Keep on testing, better!