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Globalcode – Open4education
CQRS and Event Driven Architecture
Andre Eberhardt
Globalcode – Open4education
whoami
/in/andreeberhardt
@aeberha
/eberhara
Software Specialist @ ADP
Globalcode – Open4education
motivation
Globalcode – Open4education
agenda
cqrswhat’s it?why does it matter?when should (or not) it be applied?
event driven architectureintrousage with cqrs
sample app...
Globalcode – Open4education
what’s cqrs?
Command
Query
Responsibility
Segregation
Globalcode – Open4education
an architectural model?
NO
Globalcode – Open4education
a pattern?
YES!
Globalcode – Open4education
it’s not this...
Globalcode – Open4education
it could be this...
Globalcode – Open4education
... or even this!
Globalcode – Open4education
so, why does it matter?
Scalability
Reduce complexity (domain level)
Flexibility
Focus on domain logic / proper technology
Task-based operations / Stale data
Globalcode – Open4education
but... and the downsides?
Learning curve / fear of change
Complexity
Eventual consistency
"Most people using CQRS (and event sourcing too) shouldn't have done so." —Udi Dahan
Globalcode – Open4education
so when should I apply it?
Decision per Bounded Context
Collaborative / complex domainsMultiple operations in parallel (stale data)
Distributed / specialized teams
Command vs Read performance
Globalcode – Open4education
and when avoid it?
Simple / static CRUD
Sequential operations
Non-collaborative bounded contexts
Eventual consistency not acceptable
Globalcode – Open4education
event driven architecture
Globalcode – Open4education
what’s that now?
State changes
Event consumers vs producers
Fire-and-forget
Happens in the past“User created”, “User deleted”, ...
Globalcode – Open4education
and why is that good?
Immutable states
Loosely coupled apps
Fits well with some rock stars (CQRS and DDD)
Async process
State reproducibility
Globalcode – Open4education
request-driven soa
Globalcode – Open4education
event driven architecture
Globalcode – Open4education
cqrs without events...
Globalcode – Open4education
cqrs and events?!
Globalcode – Open4education
lessons learned
Start small and extensible
Scale when you need to scaleAvoid huge / complex architectures for small problemsAvoid scaling when you don’t need to
Globalcode – Open4education
gurus
Greg Young
Martin Fowler
Udi Dahan
Globalcode – Open4education
sample app...
https://github.com/eberhara/sample-cqrs
Globalcode – Open4education
thank you :)
/in/andreeberhardt
@aeberha
/eberhara
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