Benjamin Nothdurft
Software Craftsman, DevOps, @jenadevs @jugthde Founder/Speaker, Traveller & Cyclist – focusing on Continuous Delivery Pipelines, Automation, Docker, Selenium, Java
The Power of Event Storming
Benjamin Nothdurft
codecentric AG
DOAG Conference
2019-10-11 in Nürnberg
From a Pile of Sticky Notes to a Domain-Driven Design Microservices Architecture
@dataduke
Context
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As Developers...
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Benjamin Nothdurft
@dataduke
Context
Basics
Iterations
Architecture
Take-Aways
Agenda
Basics
@dataduke
What is Event Storming?
-
lightweight method to model a domain
- within an event storming workshop we work in iterations to add layer by layer of elements to sharpen the picture of a domain
-
typical elements
- domain events, commands, aggregates
-
issues/hot spots, chances
-
external systems, read models, policies
-
users/actors, timers, loops
Why do we use Event Storming?
-
knowledge distribution
- bring together people from different silos
- domain experts/analysts/developers/architects
-
enforcing a sharp timeline
- experts will create locally ordered sequence of events
- trigger long-awaited conversation
-
following steps
- structure will emerge
- people and systems will be displayed
- every layer sparkles a new type of conversation
- ...
Iterations
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Phase: Kick-off
-
Invite the right people (diversity in background/attitude, knowledge, curiosity)
-
room setup (space to move, plenty of sticky notes/markers/food, timer)
-
workshop structure (incremental notation, mostly stand-up, time-boxed warm-up e.g. Cinderella fairy tale story, explicit goal is to explore business process, uncomfortable/chaotic/awkward > take care of people, icebreaker)
Phase: Chaotic Exploration
product added to cart
-
domain event (past tense)
-
orange sticky note
-
relevant for domain experts
Phase: Enforcing the timeline
-
Make sure there’s enough space available
-
Choose a sorting strategy (Pivotal Events, Swimlanes, Temporal Milestones, Chapters Sorting, or Combination)
-
e.g. pivotal/Key Events: Article Added to Catalogue, Order Placed, Order Shipped, Payment Received and Order Delivered
Example (First Iteration)
Phase: Explicit walk-through
- talking about events while walking in front of the surface
- manage discussions (mark hot spots)
- telling the story backward (starting at terminal events)
- emerging consistent narrative
Phase: Problems and opportunities
-
looking for key impediments, problems and opportunities (10-15 minutes time-box to capture risks and ideas)
Phase: Pick your problem
- arrow voting (target most important with e.g. 2x blue arrows per person)
First Iteration with all phases
Command-Event-Pairs
-
command (present tense)
-
blue sticky note
-
triggers a domain event
product add to cart
Aggregates / Entities
-
aggregate/entity
-
yellow sticky note
-
data that is interacted with
product
Borders & Flow
-
find borders where a domain model has a different meaning
-
domain events flow between different models
Bounded Contexts
-
bounded context/sub-domain
-
red sticky note
-
core name that is relevant/valid
checkout
Outcome / Big Picture
-
narrative/stories/user journey
-
line(s)
-
multiple storytellings
-
common language for everyone
Example
More Elements...
Iterate / Color Puzzle Thinking
event
command
external system
policy
user
user
command
-
add new colours/sticky notes: e.g. policies
-
challenging value (discover new opportunities, inconsistencies)
-
reveal pain points
-
enable cross-perspective conversation
Example (End of Day 2)
Example (End of Day 2)
Patterns
- Add more space
- Be the worst
- Conquer first, Divide later
- Do first, Explain later
- Fuzzy Definitions
- Guess First
- Icebreaker
- Go Personal
- Keep your mouth shut
- Make some noise
- One man one marker
- The Right to be wrong
- ...
Anti-Patterns
- Ask questions first
- Big table at thhe center of the room
- Committee
- Do the right thing
- Dungeon Master
- Follow the leader
- Human bottleneck
- Religion war
- The spoiler
- Start from the beginning
- ...
Architecture
@dataduke
Example
provider-ui
storefront-ui
merchant-ui
Frontend
api proxy
tenant
auth
Core
business unit
site
shop
Shop Admin
Product
product
. . .
. . .
. . .
. . .
Bounded Contexts > Microservices
Exe / Jar / Zip
Objects
Classes
OOP
Design Patterns
Modules
Layers
Project
Developer cares about ...
Strategic Design
Service
Service
Service
Sub-Domain
Sub-Domain
Domain
Domain-Driven-Design
Exe / Jar / Zip
Objects
Classes
OOP
Design Patterns
Modules
Layers
Project
Tactical Design
Upstream / Downstream
Call Flow
Model Flow
Context Map Patterns Categorized
Model Flow
Upstream Patterns
-
Open Host Service
-
Event Publisher
Downstream Patterns
-
Customer / Supplier
-
Conformist
-
Anticorruption Layer
In-Between Patterns
-
Shared Kernel
-
Published Language
-
Seperate Ways
Upstream System
Down-stream System
provider-ui
storefront-ui
merchant-ui
Frontend
api proxy
tenant
auth
Core
business unit
site
shop
Shop Admin
Product
product
. . .
. . .
. . .
. . .
Microservices
Context Map
Strategic Design Tools
Tactical Design Tools
Building Blocks in DDD
Take-Aways
@dataduke
Try Event Storming!
Ubiquitous Language
- use the same vocabulary for the same concepts
- e.g. domain experts, analysts, developers use same language to describe a problem on the whiteboard
Bounded Context
- area of the problem space where the ubiquitous language is valid
- e.g.
- customer in sales = social interests, likes, needs
- customer in support = history, tickets
- customer in accounting = method of payment
- customer in order = addresses, availability
Most important terms... I/II
Domain Model
- interpretation of reality
- includes the chosen aspects for implementation
- refers to the abstraction of the subdomain
Most important terms... II/II
A domain model is to a bounded context
what classes are to objects
Context Map
- relation between bounded contexts
References
For more Domain Modelling
Questions?
@dataduke
Benjamin Nothdurft
codecentric AG
Developer Open Space
2019-10-11 in Leipzig
The End...
Facilitation
@dataduke
Elements
Facilitation Hints
Text
- invite the right people
- room setup
- workshop structure (possible warm-up excercise: Cinderella etc.)
Each sub-domain is implemented as vertical:
- represents a deployable unit (one or more)
- is exclusively responsible for its services
- owns its data
- communicates with other verticals predominantly by using asynchronous messaging
- provides a REST-API to leverage access to its function
Sub-Domains / Verticals
Strategic Design Tools
Iterate / Color Puzzle Thinking
event
command
external system
policy
user
read model
user
command
-
add new colours/sticky notes: e.g. policies
-
challenging value (discover new opportunities, inconsistencies)
-
reveal pain points
-
enable cross-perspective conversation
Process
Process
Actors & Policies
Let's start!
Exe / Jar / Zip
Objects
Classes
OOP
Design Patterns
Modules
Layers
Project
Developer cares about ...
Tactial Design
Service
Exe / Jar / Zip
Objects
Classes
OOP
Design Patterns
Modules
Layers
Project
The Power of Event Storming Benjamin Nothdurft codecentric AG DOAG Conference 2019-10-11 in Nürnberg From a Pile of Sticky Notes to a Domain-Driven Design Microservices Architecture @dataduke
Power of Event Storming
By Benjamin Nothdurft
Power of Event Storming
2019-11-21 Event Storming at DOAG Nuremberg
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