What is Software Architecture… Architectural Styles
PV260 Software Quality
1
Ondřej “Ondra” Krajíček


ondrej.krajicek@ysoft.com


@OndrejKrajicek
Architectural Styles
Architectural Styles
• Tiered Architecture

• Hexagonal Architecture

• Onion Architecture

• Object Oriented Architecture

• Service Oriented Architecture

• Microservices
Which one is the best one?
• Consistency
• Cohesion
• Coupling
• Clarity
Cost of
Change
(a
ff
ected by technical debt)
How can we measure
technical debt?
Principles over Patterns.
Consistency
Module, Data, Service, Interaction Dependencies.
Coupling
https://www.javatpoint.com/software-engineering-coupling-and-cohesion
Well-Designed or Leaking Abstractions.
Cohesion
https://www.javatpoint.com/software-engineering-coupling-and-cohesion
Everyone understands why, how and what to do. System deteriorates
slower and technical debt does not grow quickly.
Clarity
Replaceable Architecture
Wait, what?
Osaka Castle
Giza Pyramids
• Built to last: hundreds and thousands of years.
• Built to survive natural disasters, especially earthquakes (shinbashira).
• Both have very different architecture.


• You cannot replace one with the other.


• Why would you?
Replaceable as in Having rather low Cost of Change
How to decrease Cost of Change?
2-Tier Architecture
• Original Client / Server

• Business Logic is implemented on the client,
server or both.

• What are the issues?
3-Tier Architecture
• Decouple presentation from business logic.
Business logic is isolated from client and
server.

• Business layer often historically hosted in
application servers with obscure
technologies (j2ee, Microsoft ASP, PHP,
ColdFusion, etc.).

• How is it di
ff
erent from 2-Tier?
https://en.wikipedia.org/wiki/Multitier_architecture#/media/File:Overview_of_a_three-tier_application_vectorVersion.svg
Onion Architecture
• Built on the observation that most / all
interfaces are alike.

• Outer layers depend on inner layers.

• Inner layers must not depend on outer
layers.

• Enforces Inversion of Control.

• How is it di
ff
erent from N-Tier?
Hexagonal Architecture
• Ports and Adapters Architecture

• Sometimes Onion and Hexagonal are viewed
as the same.

• Hexagonal Architecture is more explicit and
structured.

• Recommended reading:

https://herbertograca.com/2017/11/16/
explicit-architecture-01-ddd-hexagonal-
onion-clean-cqrs-how-i-put-it-all-together/
The Clean Architecture
• Onion + Screaming Architecture.


• Independent of Frameworks.


• Testable: all parts and as a whole.


• Independent of Interfaces.


• Independent of the data store /
database / object persistence.


• Independent of any external
impact.
Microservices also known as the current silver bullet.
https://www.cgl.ucsf.edu/Outreach/pc204/NoSilverBullet.html
Organization structure determines
system architecture / design.
https://medium.com/@learnstu
ff
.io/conways-law-in-software-
dev-3aa6324ead52
As the systems get larger, complexity grows quickly and systems
become unmanageable.
http://www.laputan.org/mud/mud.html#BigBallOfMud
https://medium.com/raa-labs/part-1-domain-driven-design-like-a-pro-f9e78d081f10
• Split system in a set of loosely coupled, cohesive services.
• Each service does only one thing and does it well.
• Each service is represented only by its API.
• Each service has its own data.
Microservices
https://medium.com/hashmapinc/the-what-why-and-how-of-a-microservices-architecture-4179579423a9
What are the challenges of Microservices?
Compensating for high decentralisation. Patterns are emerging.
API Gateway Pattern Thank you NETFLIX!
https://microservices.io/patterns/apigateway.html
Key Takeaways
Architectural style is a choice driven by stakeholder values.
Everyone talks about microservices, yet that does not make it the
silver bullet.