Harnessing Domain Driven Design

Harnessing Domain Driven Design
Gayathri Thiyagarajan
Lead Software Engineer Capgemini
Andrew Harmel
Law Principal Software Engineer Capgemini

@YourTwitterHandle#YourSessionHashtag
Harnessing Domain Driven
Design for Distributed Systems
Gayathri Thiyagarajan &
Andrew Harmel-Law,
Capgemini UK
http://capgemini.github.io
@gaythu_rajan / @al94781#harnessing_ddd

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Who are we?

Who are we?

“Microservice”?

“Microservice”? (cont.)

Microservices ROCK!
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Microservices are HARD

“Getting service boundaries wrong
can result in having to make lots
of changes in service-service
collaboration. An expensive
operation.”
from Sam Newman, “Building Microservices”
(section: When shouldn’t you use Microservices)
Boundaries are HARDEST

Microservices LOVE DDD
cc: {AndreaRenee} - https://www.flickr.com/photos/30282864@N02
“Despite the hype
[microservices] probably giv[e]
us the best environment we
have ever had for doing
Domain-Driven Design”
(Interview with Eric Evans at 2015 DDD Exchange)

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Unfortunately...

Some steps...
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The Core
How DDD helps our CODE
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Ubiquitous Language
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Hands-On Modellers
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The Misapplied
How DDD helps our overall Architecture
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The Important Bits
• Models
• Aggregates
• Contexts
• Bounded Contexts
• Context Maps

Shared Payment Services
Our Case Study:
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Models
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Aggregates
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Contexts
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Bounded Contexts
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Context Maps
cc: roger4336 - https://www.flickr.com/photos/24736216@N07

Why Aggregates?

Aggregate == Microservice

But, Aggregate !=
Microservice (not always)

1. Draw a Model and begin to implement it
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An Approach

2. As you draw it and code it, listen to the Language and
cultivate your Model accordingly
An Approach

3. Identify your Aggregates - these are your starter
Microservices
An Approach

An Approach
Microservices
4. When you hit pain points (indicated by the Language) split
into different Bounded Contexts to resolve

Microservices
4. When you hit pain points (indicated by the Language) split
into different Bounded Contexts to resolve
5. Revisit your Bounded Contexts now you know more about
how each Aggregate - you may end up splitting them
An Approach

Done?
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The Ignored
How DDD helps our Teams Organise
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Customer-Supplier
Partnership Anti-Corruption Layer
Upstream
Downstream

Shared
Kernel
Separate
Ways
Anti-
Corruption
Layer
Partner-
ship
Conform-
ist
Open
Host
Service
Customer
/
Supplier
ControlOverAssociatedTeams
Communications Commitment / Capability of Teams

Upstream/Downstream
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Partnership
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Partnership

Customer-Supplier
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Customer-Supplier

@gaythu_rajan / @al94781#harnessing_ddd @gaythu_rajan / @al94781#harnessing_ddd

Anti-Corruption Layer

Anti-Corruption Layer
Upstream
Downstream

Done Done
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Take Home Messages
cc: Manoj Kengudelu - https://www.flickr.com/photos/11767573@N02
• Find the right Microservices - or you’ll pine for
the Monolith

Take Home Messages
the Monolith
• Don’t get confused about BCs - they will fall
out if you listen to the Language

Take Home Messages
the Monolith
• Organise around your services better - apply
the Strategic Patterns

Take Home Messages
the Monolith
• Organise around your services better - apply
the Strategic Patterns
• Be inspired to do more Domain Driven Design

And Finally...
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Questions Please
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Oh, and we (Capgemini ) are hiring!
(visit bit.ly/cg-jvm-jobs-ddd)
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Read More...
• https://capgemini.github.io/architecture/
microservices-reality-check/
why-microservices-are-right-for-us-pt1/
microservices-like-change/
microservices-gotchas/

Harnessing Domain Driven Design

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