The Three Dimensions of System Design: Coordination Models
Welcome to the third instalment in our series exploring the fundamental dimensions of system design! After examining Consistency and Communication Models, we're now diving into how systems coordinate their actions. Today, we'll explore our third dimension: Coordination Models.
Understanding Coordination Models
Think of coordination models like different ways of organising a restaurant kitchen. In an orchestrated kitchen, the head chef (conductor) calls out orders and directly coordinates all activities. In a choreographed kitchen, each station chef knows their role and reacts to events (orders coming in, dishes being ready) without central coordination.
The Two Modes of Coordination
Orchestration 🎭
Orchestration is like a conductor leading an orchestra - one central entity directs and controls the entire flow of operations.
Key Characteristics:
Centralised control
Clear visibility of process
Direct error handling
Sequential flow control
Explicit coordination
Common Use Cases:
Business process workflows
Order processing systems
Payment processing
Multi-step validations
Choreography 💃
Choreography is like a street dance performance - each participant knows their role and reacts to others' actions without central direction.
Key Characteristics:
Decentralised control
Independent participants
Event-driven interactions
Emergent behavior
Implicit coordination
Common Use Cases:
Microservices ecosystems
Event-driven architectures
IoT systems
Real-time data processing
NFR Alignment Scores 📊
Let's examine how each coordination model aligns with different NFRs:
*purely subjective measuring
Orchestration
Reliability: ⭐⭐⭐⭐⭐
Availability: ⭐⭐
Scalability: ⭐⭐
Performance: ⭐⭐⭐
Maintainability: ⭐⭐⭐⭐
Choreography
Reliability: ⭐⭐⭐
Availability: ⭐⭐⭐⭐⭐
Scalability: ⭐⭐⭐⭐⭐
Performance: ⭐⭐⭐⭐
Maintainability: ⭐⭐⭐
A handy rule of thumb
When in doubt, here is a handy rule of thumb that you can use:
Architect's Alert 🚨
Remember: The choice between orchestration and choreography isn't just about technical elegance. Orchestration provides better visibility and control but can become a bottleneck. Choreography offers better scalability but can make it harder to understand and debug the system as a whole.
System Impact Considerations
Control Requirements 🎮
Process visibility needs
Error handling requirements
Audit requirements
Compliance needs
Scale Considerations 📈
Number of participants
Transaction volume
Geographic distribution
Growth projections
Organisational Factors 👥
Team structure
Operational capabilities
Monitoring requirements
Development velocity
Best Practices
Clear Boundaries
Define service responsibilities
Document interaction patterns
Establish error handling
Set monitoring points
Smart Defaults
Design for failure
Plan for partial success
Include timeout handling
Consider replay capabilities
Evolution Strategy
Start simple
Plan for growth
Document patterns
Monitor behaviour
Anti-Patterns to Avoid ⚠️
The All-Knowing Orchestrator
Too much central control
Bottleneck creation
Single point of failure
The Chaos of Freedom
No clear process ownership
Difficult to debug
Unpredictable behaviour
Mixed Models Mess
Unclear responsibilities
Confusing interactions
Maintenance nightmare
Conclusion
Choosing between orchestration and choreography is about finding the right balance for your specific context. While orchestration provides better control and visibility, choreography offers better scalability and autonomy. The key is understanding your requirements and choosing accordingly.
Next in our series, we'll explore how these three dimensions (Consistency, Communication, and Coordination) interact and combine to create different architectural patterns.