PRACTICAL DDD: BOUNDED CONTEXTS + EVENTS => MICROSERVICES

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BOUNDED CONTEXTS + EVENTS => MICROSERVICES PRACTICAL DOMAIN-DRIVEN DESIGN @indu_alagarsamy

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Titanium Sponsors Platinum Sponsors Gold Sponsors

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@indu_alagarsamy

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Product Name Description Product Images List Price Shipping Options Stock Availability Customer Reviews Dimensions @indu_alagarsamy

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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

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UNIFIED MODELS ARE HARD @indu_alagarsamy

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BOUNDED CONTEXT IS A SAFE SPACE Source: https://www.airbnb.com/rooms/15448688?guests=1&adults=1

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CONTEXTS PROVIDE CLARITY @indu_alagarsamy

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FINDING THE BOUNDARY @indu_alagarsamy

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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?

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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

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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

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More info on finding boundaries: http:// go.particular.net/kcdc19

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HOW DO BOUNDED CONTEXTS COMMUNICATE? THE AIRLINE EXAMPLE @indu_alagarsamy

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COMMANDS & EVENTS @indu_alagarsamy Something of importance happened Do something Domain Event Command

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http://images.fanpop.com/images/image_uploads/300-Movie-Publicity-Still-300-222345_1500_790.jpg

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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

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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

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Mycenae, Greece Multiple messages can take part in a business process AircraftTypeHasChanged NotifyCustomer RebookFlight BookingWasCancelled @indu_alagarsamy FLIGHT PLANNING BOUNDED CONTEXT BOOKING BOUNDED CONTEXT

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Mycenae, Greece Saga Pattern BUSINESS POLICY STATE @indu_alagarsamy

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@indu_alagarsamy EVENTSTORMING Source: dddeurope.com

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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

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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

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Booking Context AircraftType Was Changed class AircraftTypeWasChangedHandler : IHandleMessages { Handle(AircraftTypeWasChanged msg, MessageHandlerContext context) { // Find all the relevant booking references context.Send(new RebookFlight{…}); } }

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Booking Context RebookFlight class RebookFlightHandler : IHandleMessages { Handle(RebookFlight msg, MessageHandlerContext context) { // Find a good proposed route context.Publish(new BookedFlightWasChanged{…}); } }

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Booking Context BookedFlight WasChanged Booking WasCancelled Cancellation GracePeriodElapsed public class BookingChangePolicy : Saga, IAmStartedByMessages, IAmStartedByMessages, IHandleTimeouts @indu_alagarsamy

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@indu_alagarsamy NAMING THINGS ARE HARD

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@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

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class AircraftTypeWasChangedHandler : IHandleMessages class ProposeNewRebookingWhenAircraftTypeWasChanged : IHandleMessages HEALTHY OBSESSION WITH LANGUAGE @indu_alagarsamy

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public class BookingChangePolicy : Saga, IAmStartedByMessages, IAmStartedByMessages, IHandleTimeouts class GracePeriodForAcceptingRebookings : Saga, IAmStartedByMessages, IAmStartedByMessages, IHandleTimeouts HEALTHY OBSESSION WITH LANGUAGE @indu_alagarsamy

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public class AircraftTypeWasChanged { public OldAircraftId {get; set;} } MAKE MESSAGES IMMUTABLE @indu_alagarsamy Get rid of the public setters Set the properties at construction time

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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

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LoyaltyStatus ProcessLoyaltyInfo() @indu_alagarsamy Temporal Coupling AircraftTypeHasChanged RebookingWasProposed PROPOSE REBOOKING Booking Context GetLoyaltyStatus(customerId) PROMOTE CUSTOMER Loyalty Context

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BOOKING LOYALTY CustomerWasPromotedToGold CustomerWasPromotedToPlatinum Customer PromotionInfo FLIGHT PLANNING AircraftTypeHasChanged ProposeRebooking @indu_alagarsamy Make Autonomous Decisions

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Source: http://www.gameslayer.org/articles/My_Tron_Style_Working_Environment-4/work-environment-02.jpg DEPLOYMENTS

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ProposeRebooking v1.1 ProposeRebooking v1.0 AircraftTypeHasChanged SIDE BY SIDE @indu_alagarsamy

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ProposeRebooking v1.1 ProposeRebooking v1.0 AircraftTypeHasChanged ROLLBACKS Error Queue @indu_alagarsamy

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MONITORING @indu_alagarsamy

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@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

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Sept 16-20, 2019 MORE ON DDD Feb 3-7, 2020 exploreddd.com dddeurope.com Domain-Driven Design Tackling complexity in the heart of software - Eric Evans @indu_alagarsamy https://leanpub.com/ddd_first_15_years

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THANK YOU @indu_alagarsamy https://indu.dev