I’ve just watched this presentation by Chris Richardson about Building and Deploying Microservices with Event Sourcing.

These are notes to myself taken while watching the presentation:

Monolithic apps lock you in the technology you choose at the beginning of the project.

Events used to achieve eventual consistency across distributed services / datastores:

• Microservices publish events when state changes
• Microservices subscribe to events
  • maintain eventual consistency (multiple aggregates in multiple datastores)
  • synchronize replicated data
• An event needs to be published atomically every time a domain entity changes its state

Event sourcing: for each aggregate persist the events that lead to a particular state instead of the state itself

Persisting events: json is a good choice because of its loose mapping mechanism

Optimize by using snapshots:

• serialize a memento of the aggregate
• load latest snapshot + subsequent events

Business benefits of event sourcing:

• built-in audit log
• enables temporal queries
• preserved history

Technical benefits:

• No more O/R mapping - we are just persisting events

Drawbacks:

• Handling duplicate events / out-of-order

Think of a microservice as a DDD aggregate

For view requests use CQRS & denormalized views

Use an Event Archiver that subscribes to all events: enables analytics.