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Pitfalls Of Building Large-Scale Apps By Jeffrey Sogolov
@gsogol
Network Is Reliable
Do things
REALLY FAIL?
Microsoft’s Datacenter
5.2 Devices
40.8 Links P
er Day
59,000 Packets Loss
HP’s Datacenter
Connectivity
11.4% Support Tickets
2hr 45min Down Time For Support Tickets
HIGHEST
Chubby
61 Outages 700 IN days
aphyr.com/posts/288-the-network-is-reliable
See more
Latency Is Not A Problem
Bandwidth Is Infinite
OOH…
GIGA
1 Gigabit
50 MB 128 MB
Topology Won’t Change
Subnets Moving
Added Firewalls
Hardcoded IPs
Same Rack?
Administrator Knows
WHAT TO DO
Network IS Homogeneous
System Is Atomic
Big Ball Of Mud
The System Is Finished
Effort
Time
“Normal Project”
Product
“Finished”
Rewrite
Original date
Business Logic Should Be Centralized
Entities
Calculations/ Validations
Services
What Is Loose
Afferent coupling (Ca) – who depends on you Incoming coupling
Efferent coupling (Ce) – on who you depend
Outgoing coupling
Coupling ?
Ca
Ce
Ca VS Ce
Framework
DTOs
UI
>
>
1.
2.
3.
A Touch OF
Platform
Coupling
A Touch OF
Platform
Coupling
VS
A Touch OF
Spatial
Coupling
Product
Synchronous Call
Waiting Working
Return
Pricing
A Touch OF
Temporal
Coupling
Product
Synchronous Call
Waiting Working
Return
Pricing
What Is The Business Telling YOU?
So What Is Loose Coupling?
Efferent
Afferent
Platform Temporal
Spatial
What do you choose? Style Over Substance!
History Repeats Itself
Same monolithic procedural code… …just with HTTP to make it really fly!
So…Web Services Are Like…
But Wait…
One Problem…
Asking 100 engineers… how to solve a problem? …how many answers will I get?
Martin Fowler’s Definition of Architecture
“Design decisions you wished you've gotten right at the beginning of the project”
Encapsulation
Composition OR Inheritance
Composition OVER Inheritance
Services Should:
• Be autonomous & self-governing • Contain explicit boundaries • Well…be encapsulated
Chain Of Services am I highly encapsulated & autonomous?
iTunes Example
What Does Responsibility Mean? • Encapsulation • Alignment • With web services,
is data encapsulated?
Pricing
Front Office
Marketing
Back Office
Reporting
4+1 Architectural Views
Let’s Run A Race…
Page != Same Service
Keep it DRY!
Couple Of Rules Then
• Service != system (does not mean separate process) • It’s about logical responsibility, Not physical • Usually…software system = project the team is working on • Pricing, reviews, inventory cut across systems
Conway’s Law
“ Organizations which design systems ... are constrained to produce designs which are copies of the communication structures of these organization”
Teams’ Effect
Architecture is as much of a people component as a software component
Thank You.
Twitter: @gsogol LinkedIn: linkedin.com/in/jeffreysogolov/
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