Practical DDD: Bounded Contexts + Events => Microservices

Domain Driven Design and Messaging go hand in hand, like a warm chocolate brownie paired with vanilla ice-cream! DDD is a software discipline that allows you to move faster and write high-quality code. The whole point is to align the software you write to be flexible with the business changes. When you start to use the technology of messaging to communicate between clean and well-defined bounded contexts you get to remove temporal coupling. And voila, you now have microservices that are built for autonomy from the ground up. Sounds perfect?

In this talk, discover this intersection of DDD as a software discipline with messaging as a technology counterpart. Build reliable systems that can scale with the business changes.

Transcript

1. BOUNDED CONTEXTS + EVENTS => MICROSERVICES PRACTICAL DOMAIN-DRIVEN DESIGN @indu_alagarsamy
2. @indu_alagarsamy
4. Product Name Description Product Images List Price Shipping Options Stock Availability Customer Reviews Dimensions @indu_alagarsamy
5. Sales Inventory Shipping WHAT IS A PRODUCT ? It’s a thing that has a description, images, price It’s a thing that is either available or not It’s a thing that has weight and dimensions that needs to be packaged @indu_alagarsamy
6. UNIFIED MODELS ARE HARD @indu_alagarsamy
7. BOUNDED CONTEXT IS A SAFE SPACE Source: https://www.airbnb.com/rooms/15448688?guests=1&adults=1
8. CONTEXTS PROVIDE CLARITY @indu_alagarsamy
9. FINDING THE BOUNDARY @indu_alagarsamy
10. Product Name Description Product Images List Price Shipping Options Stock Availability Customer Reviews Dimensions @indu_alagarsamy Do you need transactional consistency for updating the description and the stock availability?
11. Sales Inventory Shipping Description Product Images List Price Stock Availability Shipping Options SPLIT THE MODEL ACCORDING TO TEAMS OR DEPARTMENTS Dimensions Product Product Product Dimensions @indu_alagarsamy
12. SPLIT THE MODEL ACCORDING TO BUSINESS PROCESSES @indu_alagarsamy Get $70 off instantly: Pay $0.00 upon approval for the Amazon Prime Rewards Visa card Get it tomorrow. Order within 1hr 53 mins and choose One-Day Shipping at checkout
13. More info on finding boundaries: http://go.particular.net/ exploreddd19
14. HOW DO BOUNDED CONTEXTS COMMUNICATE? THE AIRLINE EXAMPLE @indu_alagarsamy
15. COMMANDS & EVENTS @indu_alagarsamy Something of importance happened Do something Domain Event Command
16. WHEN an aircraft type is changed: Passenger gets notified with a new booking proposal Passenger can cancel flight Passenger can accept proposed booking @indu_alagarsamy
18. Mycenae, Greece A Business Process can be triggered by an event from a different bounded context AircraftTypeHasChanged FLIGHT PLANNING BOUNDED CONTEXT BOOKING BOUNDED CONTEXT WHEN an aircraft type is changed @indu_alagarsamy
19. Mycenae, Greece Multiple messages can take part in a business process AircraftTypeHasChanged NotifyCustomer RebookFlight BookingWasCancelled @indu_alagarsamy FLIGHT PLANNING BOUNDED CONTEXT BOOKING BOUNDED CONTEXT
20. Mycenae, Greece Saga Pattern BUSINESS POLICY STATE @indu_alagarsamy
21. @indu_alagarsamy EVENTSTORMING Source: dddeurope.com
22. Flight planning context Booking context MODELING USING EVENT STORMING @indu_alagarsamy Aircraft type has changed Booked Flight Was Changed Booking was confirmed Booking was cancelled
23. EVENT STORMING @indu_alagarsamy Aircraft type was changed Rebook Flight Booked Flight Was Changed Notify customer about flight change Request time out (5 days) Booking was confirmed Booking was cancelled
24. Booking Context AircraftType Was Changed class AircraftTypeWasChangedHandler : IHandleMessages <AircraftTypeWasChanged> { Handle(AircraftTypeWasChanged msg, MessageHandlerContext context) { // Find all the relevant booking references context.Send(new RebookFlight{…}); } }
25. Booking Context RebookFlight class RebookFlightHandler : IHandleMessages<RebookFlight> { Handle(RebookFlight msg, MessageHandlerContext context) { // Find a good proposed route context.Publish(new BookedFlightWasChanged{…}); } }
26. Booking Context BookedFlight WasChanged Booking WasCancelled Cancellation GracePeriodElapsed public class BookingChangePolicy : Saga<BookingChangePolicyData>, IAmStartedByMessages<BookedFlightWasChanged>, IAmStartedByMessages<BookingWasCancelled>, IHandleTimeouts<CancellationGracePeriodElapsed> @indu_alagarsamy
27. @indu_alagarsamy NAMING THINGS ARE HARD
28. @indu_alagarsamy Aircraft type was changed Rebook Flight Booked Flight Was Changed Notify customer about flight change Booking was confirmed Booking was cancelled Passenger gets notified with a new booking proposal Propose Rebooking Rebooking Was Proposed Notify customer about proposed rebooking Request time out (5 days) Rebooking was accepted
29. class AircraftTypeWasChangedHandler : IHandleMessages<AircraftTypeWasChanged> class ProposeNewRebookingWhenAircraftTypeWasChanged : IHandleMessages<AircraftTypeWasChanged> HEALTHY OBSESSION WITH LANGUAGE @indu_alagarsamy
30. public class BookingChangePolicy : Saga<BookingChangePolicyData>, IAmStartedByMessages<BookedFlightWasChanged>, IAmStartedByMessages<BookingWasCancelled>, IHandleTimeouts<CancellationGracePeriodElapsed> class GracePeriodForAcceptingRebookings : Saga<GracePeriodForAcceptingRebookingsData>, IAmStartedByMessages<RebookingWasProposed>, IAmStartedByMessages<BookingWasCancelled>, IHandleTimeouts<CancellationGracePeriodElapsed> HEALTHY OBSESSION WITH LANGUAGE @indu_alagarsamy
31. public class AircraftTypeWasChanged { public OldAircraftId {get; set;} } MAKE MESSAGES IMMUTABLE @indu_alagarsamy Get rid of the public setters Set the properties at construction time
32. WHEN Aircraft type is changed: Passenger gets notified with a new booking proposal Passenger can cancel flight Passenger can accept proposed booking @indu_alagarsamy Only applies to passengers who are flying business class or first or Platinum loyalty
33. LoyaltyStatus ProcessLoyaltyInfo() @indu_alagarsamy Temporal Coupling AircraftTypeHasChanged RebookingWasProposed PROPOSE REBOOKING Booking Context GetLoyaltyStatus(customerId) PROMOTE CUSTOMER Loyalty Context
34. BOOKING LOYALTY CustomerWasPromotedToGold CustomerWasPromotedToPlatinum Customer PromotionInfo FLIGHT PLANNING AircraftTypeHasChanged ProposeRebooking @indu_alagarsamy Make Autonomous Decisions
35. Source: http://www.gameslayer.org/articles/My_Tron_Style_Working_Environment-4/work-environment-02.jpg DEPLOYMENTS
36. ProposeRebooking v1.1 ProposeRebooking v1.0 AircraftTypeHasChanged SIDE BY SIDE @indu_alagarsamy
37. ProposeRebooking v1.1 ProposeRebooking v1.0 AircraftTypeHasChanged ROLLBACKS Error Queue @indu_alagarsamy
38. @indu_alagarsamy Talk to domain experts. Event storm with them. Models are not perfect Evolve and refactor with an obsession for domain language Strive for Autonomy. Use events to communicate between bounded contexts
39. THANK YOU @indu_alagarsamy https://indu.dev