Spring I/O 2019 presentation showcasing features of Axon Framework and Spring Boot that make building Event Driven Microservices based on CQRS and DDD a breeze.

1. @allardbz
Allard Buijze
@allardbz
Event-Driven Microservices
with Axon and Spring Boot
Excitingly boring!

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> java –jar my_awesome_app.jar
Hello world!
> _
> _

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Production is no place
for excitement!

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“Universal ‘BBC’ architecture”
Box Box Cylinder
Source: Ted Neward

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Source: http://www.sabisabi.com/images/DungBeetle-on-dung.JPG

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“Universal Microservices
architecture”

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Number of deployment units
Modularity
“Evil anti-modularity forces”

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$

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Location transparency
A Component should not be aware, nor make any
assumptions, of the location of Components it
interacts with
A component should neither be aware of nor make any
assumptions about the location of components it interacts with.
Location transparency starts with good API design
(but doesn’t end there)

10. @allardbz
Microservices Messaging
Commands Events Queries
Route to single handler
Use consistent hashing
Provides confirmation/result
Distribute to all logical handlers
Consumers express ordering req’s
No results
Route with load balancing
Sometimes scatter/gather
Provides result
"Event" and “Message" is not the same thing

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Explicit messaging
Demo…

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Command Query Responsibility
Segregation
Command
model
Projections
Client
Events
Complex
Deployed often
Simple
Rarely depoyed
Seasonal usage
peaks
Unstable, memory
aggressive

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Accidental complexity
Useful for queries.
Not for making decisions!

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Applying CQRS
Demo…

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Events…
• How do we guarantee atomic publication of
events and state change commits?
• How do we guarantee that our events are a
truthful representation of an entity’s history

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Event Sourcing:
the truth,
the whole truth,
nothing but the truth

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State storage Event Sourcing
Event Sourcing
• OrderCreated (id: 123)
• ItemAdded (2x Deluxe Chair, €399)
• ItemRemoved (1x Deluxe Chair, €399)
• OrderConfirmed
• OrderShipped
• OrderCancelledByUser
• ReturnShipmentReceived
• id: 123
• items
– 1x Deluxe Chair - € 399
• status: return shipment rcvd

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The value of Event Sourcing
• Audit trail
• Analytics
• Improve modeling
• Given-when-testing
• …

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The power of…
Not now

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Event Sourcing
Demo…

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Replays
Event Handler
Projection
Event Handler
Projection

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Implement new projection
Demo…

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Streaming to the UI
User
Interface
Event Handler BikeRentedEventBikeRentedEvent
{
bikeId: 1324,
location: Barcelona,
renter:
}
Steven

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Subscription queries
Demo…

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$
You are here…

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Exchange
Queue
Queue
Event Store

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Distributing components
Live coding…

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Tracing
Live coding…

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Try it yourself
• Sources:
• https://github.com/abuijze/bike-rental-demo (‘springio’ branch)
• https://github.com/AxonFramework/AxonFramework
• Download Axon
• axoniq.io/download (includes quick-start-guide)

36. Allard Buijze
@allardbz
Thanks!
Q&A