How domain-driven design enabled scaling a big ball of mud product

@kenny_baas
@[email protected]
How domain-
driven design
enabled scaling a big ball of mud product
Photo by National Cancer Institute

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@kenny_baas
@[email protected]
Agenda
Once upon a time.....
Domain-
Driven Design 101
Why understanding the underlying needs of users was crucial
Collaborative software design and embedding software architecture in the team
From output to data-
driven outcomes through Domain-
Driven Design

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@kenny_baas
@[email protected]
Legend
user
(external)
needs
user
(internal)
Capabilities
* Simplified map - left out accepting, screening and billing and more...
Companies with
blue collar
workers
temporary
employees for
blue collar jobs
Students
age 18-25
Temporary jobs
able to work
next to studying
Looking for
a job
online
website
job openings
database
Customer
agreements
Job
openings
Pay
Custom
ERP
Recruiter
Fulfil jobs for
customer
Email
Applying
for job
account
management
account
management

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@kenny_baas
@[email protected]
Legend
user
(external)
needs
user
(internal)
Capabilities
Companies with
blue collar
workers
temporary
employees for
blue collar jobs
Students
age 18-25
Temporary jobs
able to work
next to studying
Looking for
a job
online
website
job openings
database
Customer
agreements
Job
openings
Pay
Custom
ERP
Recruiter
Fulfil jobs for
customer
Email
Applying
for job
account
management
account
management
ERP
Payrolling
payout
student

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@kenny_baas
@[email protected]
Student
18-25 years
Work single day
job when money
is needed
Company
Find blue collars
worker 'last
minute'
Legend
user
(external)
needs
user
(internal)
Capabilities
Companies with
blue collar
workers
temporary
employees for
blue collar jobs
Students
age 18-25
Temporary jobs
able to work
next to studying
Looking for
a job
online
website
job openings
database
Customer
agreements
Job
openings
Pay
Custom
ERP
Recruiter
Fulfil jobs for
customer
Email
Applying
for job
account
management
account
management
ERP
Payrolling
payout
student

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@kenny_baas
@[email protected]
Hyper flex
Written in ruby on Rails over 1.5 year time from scratch
Based on previous models from the website
Uses both the website, custom ERP and SaaS ERP
Reusable capabilities for FLEX to automate manual processes
Looks promising and strategy is to also go live in another country
Scaled up from 3 to 13 engineers, hybrid working
Keep delivering new features
Photo by Osman Rana on Unsplash

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@kenny_baas
@[email protected]
It is designed to make programming web applications easier by making assumptions about
what every developer needs to get started. It allows you to write less code while
accomplishing more than many other languages and frameworks.
Rails emphasizes the use of convention over configuration (CoC)
and follows the principle of Don't Repeat Yourself (DRY).

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@kenny_baas
@[email protected]
The Model is usually the boundary, where new features are
being added to...Ending up with a Big Ball of Mud

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@kenny_baas
@[email protected]
Team A Team B
Application
Database
Somewhere around the Millenium
Domain-
Driven Design 101

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@kenny_baas
@[email protected]
Domain models often start based on a naïve,
over simplified entity-
relationship model based on reality.
Good when you start, but when dealing with more complicated and
complex problems it will become a big ball of mud

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@kenny_baas
@[email protected]
Platonic Domain model thinking assumes idealized, abstract representations
of reality which may not always capture the intricacies of a domain. This can
be misleading in Domain-
Driven Design (DDD), especially in core or
complicated supporting domains where the nuances matter. A naïve model,
influenced by this thinking, can confine you to an oversimplified view,
potentially leading to incorrect, suboptimal and unadaptable software
solutions.
Inspired by Barry M O'Reilly
- Plato is the devil
Anti-
Pattern:
Platonic Domain Model Thinking

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@kenny_baas
@[email protected]
Users and
stakeholders
Other people involved in
designing and building software
Managers
Architects
User researcher
Analysts
.....
Code
Engineering
Team

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@kenny_baas
@[email protected]
Photo by pure julia on Unsplash
For each specific problem, a different map
For each specific problem, a different model

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@kenny_baas
@[email protected]
Job template
Jobs
Jobs
Applications
Candidate
applications
Application
Job drafting Job Fulfilment
Candidate
applications

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@kenny_baas
@[email protected]
Job template
Jobs
Jobs
Applications
Candidate
applications
Application
......
Domain-
Driven Design allows you to break down your domain
into smaller models, enabling a single team to take ownership,
even within a monolithic architecture.
This empowers the team to make changes more independently,
as it reduces the impact of those changes on other models.
Job drafting Job Fulfilment
Candidate
applications

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@kenny_baas
@[email protected]
Photo by oxana v on Unsplash
Keep the shop open:
Start extracting bounded context guided by the roadmap
What bounded context do we touch that is on the backlog?
What is something on the backlog what is hard to do with the current model?

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@kenny_baas
@[email protected]
Building a shared understanding of your domain
and use it to guide your design
_is_ the philosophy behind DDD.
The rest is principles, patterns, and practices.
— Mathias Verraes
Domain-
Driven Design 101 - Summary

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@kenny_baas
@[email protected]
Why understanding the underlying needs of users was crucial
Photo by Kelly Sikkema on Unsplash

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@kenny_baas
@[email protected]
Onboarding a student
Signup for
an account
Screen a
candidate
Upload compliancy
information and
documents
Plan a
kickstart
Check student
compliancy
Enable on
platform
Student
18-25 years
Work single day
job when money
is needed
Recruiter
Find the best job
for a student to
work on
apply for a
job
user
(external)
needs
user
(internal)
Capabilities
Account
service
Kickstart
service
Screening
service
Compliancy
service
Candidate
service

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@kenny_baas
@[email protected]
Anti-
Pattern:
Splitting a big ball of mud based
on objects or process
Refactoring a monolithic system by dividing it based on abstract or "platonic"
object concepts can lead to a fragmented architecture, an approach that's an
acknowledged anti-
pattern. This method, focused on idealized object categories
rather than concrete functionalities, often results in ambiguous module
responsibilities, impractical implementations, increased maintenance overhead,
and reduced adaptability to new requirements.
Inspired by Barry M O'Reilly
- Plato is the devil

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@kenny_baas
@[email protected]
https://medium.com/inclusive-
software/when-
why-
to-
explore-
the-
problem-
space-
16068f1a1dbc

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@kenny_baas
@[email protected]
Collaborative modelling is a visualisation
technique to analyse complex and conflict-
laden
decision-
making processes with all relevant
stakeholders and decision-
makers to create a
shared understanding.

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@kenny_baas
@[email protected]
https://www.eventstorming.com/
First time we started with only the team, on-
site.
Afterward we move it to a miro board, so we could continue online.
EventStorming became the default modelling language to design
software for the engineers.
Once the engineers had a good understanding of EventStorming, we
started doing session with stakeholders
1.
2.
3.
4.

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@kenny_baas
@[email protected]
........
........
........ ........
........ ........
........
Start with 1 Miro board, and let the team self organise and enable structuring by
splitting the miro board when needed. Giving each bounded context it's own board
* Note, the team themselves decided on using miro

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@kenny_baas
@[email protected]
Prepare templates before doing collaborative
modelling with certain key stakeholder

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@kenny_baas
@[email protected]
Distilling Bounded Context
Onboarding a student
Signup for
an account
Screen a
candidate
Upload compliancy
information and
documents
Plan a
kickstart
Check student
compliancy
Enable on
platform
Student
18-25 years
Work single day
job when money
is needed
Recruiter
Find the best job
for a student to
work on
apply for a
job
user
(external)
needs
user
(internal)
Capabilities
Candidate
screening
Candidate
compliancy
Candidate
management
Account
management
Split according to the:
Language
Departments
Users
And run through the
design with scenarios
1.
2.
3.

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@kenny_baas
@[email protected]
Photo by Trnava University on Unsplash
Start applying Domain-
Driven Design on a complicated, medium risk problem.
That way the team can experiment with the new patterns safely, and get used
too the paradigm shift without to much risk and organisation exposure

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@kenny_baas
@[email protected]
Understanding the user needs - summary
We are so caught up in the solution space
that we miss perspectives
that we forget to understand
that we miss opportunities

— Indi Young
CC BY-
SA: INDI YOUNG

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@kenny_baas
@[email protected]
Embedding
software
architecture
in the team

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@kenny_baas
@[email protected]
A paradigm shift
Command
Bounded Context
Entity Domain
Event
Event Handler
Command
Bounded Context
Entity Domain
Event
Controllers (MVC or Rest)

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@kenny_baas
@[email protected]
Photo by Nima Mot on Unsplash
"Pair programming is not just about writing code together;
it's about weaving two minds
into a singular thread of creativity and problem-
solving."

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@kenny_baas
@[email protected]
Rest
request
(command)
Rest
request
(query)
Company management
Command
Services
Aggregate
Company
Registered WorkLoc
ationUp
dated
Legacy model
Rest
request
(query)
Event Handler Do
something
else
Database
Entity table
Column Column Column
Updates
Views
Entity
Reads
request
(command)
request
(query)
Bubble context
Rest
request
(command)
Rest
request
(query)
Company management
Command
Services
Aggregate
Company
Registered
WorkLoc
ationUp
dated
Legacy model
Rest
request
(query)
Event Handler
Database
Aggregate table
Views
Entity
Reads
Read entity Table
Updates
Event Handler
Do
something
else
request
(command)
request
(query)
Autonomous
Bubble context

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@kenny_baas
@[email protected]
https://bytesizearchitecturesessions.com/
Andrea Magnorsky
Bytesize architecture session

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@kenny_baas
@[email protected]

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@kenny_baas
@[email protected]
Sustainable design decisions are decisions that
consider the sociotechnical impact of the
alternatives. After designing and analysing the
alternatives, you pick the one that gives you the
best sociotechnical trade-
off with the information
that is available. You create a feedback loop into
your design process to improve it along the way.
Over time, you will find yourself making decisions in
a similar way. This is when your decisions become
sustainable.
Collaborative software design - summary
Sociotechnical System - from https://www.researchgate.net/figure/Sociotechnical-
system-
STS-
4_fig2_306242078

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@kenny_baas
@[email protected]
Photo by Ibrahim Boran on Unsplash
driven outcomes
through Domain-
Driven Design

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@kenny_baas
@[email protected]
Job Drafting
Add
job
Job
Added Job Fullfiment
Publish
Job
Job
Published
Cancel
job
Apply
candidate
for job
Cancel
application
Job
Cancelled
Candidate
applied
for job
Application
cancelled
ACL
Create
legacy
Job
Legacy model
Create
job
Job
Created
Challenging the backlog....

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@kenny_baas
@[email protected]
Business monitoring

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@kenny_baas
@[email protected]
“We can't impose our will on a system. We can listen to what the
system tells us, and discover how its properties and our values can
work together to bring forth something much better than could
ever be produced by our will alone.”

— Donella H. Meadows
driven outcomes
through Domain-
Driven Design - Summary

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@kenny_baas
@[email protected]

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@kenny_baas
@[email protected]
Thank You #CatTax
kenny@weave-
it.org - weave-
it.org
Get the book here

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How domain-driven design enabled scaling a big ball of mud product

How domain-driven design enabled scaling a big ball of mud product

Kenny Baas-Schwegler

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