A talk for the Amsterdam ruby meetup for how to restructure rigid applications.

1. Restructuring
Rigid Applications
amsterdam.rb, April 28th 2015
Kamiel Wanrooij

2. Rigid?
• Resistent to Change
• Difficult to Reason About
• Internal and Structural Rigidness

3. Rigid - Problems
• Rigid components are hard to:
• Move
• Remove
• Repurpose
• Extend
• Compose
• Hard in execution and/or to come up with solutions

4. Causes for Rigidity
• Internal
• Complexity in code
• Naming Conventions / Coding Standards
• Focus on these last

5. Causes for Rigidity
• Structural
• Coupling
• Multi-purpose Components

6. Coupling
• Either it moves too or it breaks
• Obvious sources
• External dependencies
• Class instantiation
• Method signatures

7. Coupling
• Less obvious
• Temporal coupling
• Shared state
• Duplicate code
• Implicit (check your git log!)

8. Goals
• Embrace Change
• Single Purpose Components
• Otherwise known as
• Orthogonal Design
• Hexagonal Architecture
• Microservices
• Antifragile Software
• Reactive
• …

9. How to restructure
• You don’t

10. How to restructure
• You don’t, right now

11. How to restructure
• Identify key components
• Look for coupling
• Check consistency boundaries

12. Consistency Boundary
• Smallest areas that are linked together
conceptually
Module A Module B
Module C

13. Consistency Boundary
• Smallest areas that are linked together
conceptually
Module A Module B
Module C

14. How to restructure
• Extract a public API
• Move the component behind a generic interface
(REST)
• Event or message based
• Isolate the internal state (don’t share databases)

15. How to restructure
Module A Module B
Module C

16. Drawbacks
• More moving parts
• Consistency only enforced within boundaries
• More difficult to see the whole picture
• Infrastructure is more difficult to set up and
maintain

17. Conclusion
• Tightly coupled applications are not always bad
• Don’t start with a complex architecture
• Frameworks that work well on smaller scale can
break when you’re dealing with larger problem
domains
• Worry about the API, hide the implementation
details

18. Thank you!
• Questions? @kmile