Design Principles & Laws
Design Principles
Core principles and guidelines for system design and architecture
Single Responsibility Principle
A class should have only one reason to change
Each module, class, or function should have responsibility over a single part of the functionality provided by the software, and that responsibility should be entirely encapsulated by the class.
Benefits
- •Easier to understand and maintain
- •Reduced coupling between components
- •Better testability
- •Improved code reusability
Anti-Patterns to Avoid
- ×God objects that do everything
- ×Classes with multiple unrelated responsibilities
- ×Mixing business logic with presentation logic
Examples
Practical Tips
- 💡If you can describe a class with "and", it likely violates SRP
- 💡Extract methods that have different reasons to change
- 💡Use composition over inheritance
Related Principles:
Open/Closed Principle
Software entities should be open for extension, but closed for modification
You should be able to extend a class's behavior without modifying it. This is achieved through abstraction and polymorphism.
Benefits
- •Reduced risk of breaking existing code
- •Better maintainability
- •Easier to add new features
- •Improved code stability
Anti-Patterns to Avoid
- ×Modifying existing classes for new features
- ×Large switch statements for type checking
- ×Hardcoded dependencies
Examples
Practical Tips
- 💡Use interfaces and abstract classes
- 💡Favor composition over inheritance
- 💡Apply the Strategy pattern for varying algorithms
Related Principles:
Design for Horizontal Scaling
Build systems that can scale by adding more machines rather than upgrading existing ones
Horizontal scaling (scale-out) is generally more cost-effective and provides better fault tolerance than vertical scaling (scale-up).
Benefits
- •Better fault tolerance
- •More cost-effective scaling
- •No single point of failure
- •Easier capacity planning
Anti-Patterns to Avoid
- ×Stateful services that can't be replicated
- ×Shared mutable state between instances
- ×Single database bottlenecks
Examples
Practical Tips
- 💡Design stateless services
- 💡Use external storage for session data
- 💡Implement proper load balancing
Related Principles:
Loose Coupling
Minimize dependencies between system components
Components should be independent and communicate through well-defined interfaces, making the system more flexible and maintainable.
Benefits
- •Independent development and deployment
- •Better testability
- •Easier maintenance
- •Improved fault isolation
Anti-Patterns to Avoid
- ×Tight coupling through shared databases
- ×Direct object references across modules
- ×Synchronous call chains
Examples
Practical Tips
- 💡Use interfaces and contracts
- 💡Prefer composition over inheritance
- 💡Implement proper abstraction layers
Related Principles:
Fail Fast
Detect and report failures as early as possible
Systems should validate inputs and detect error conditions early, rather than allowing invalid states to propagate through the system.
Benefits
- •Easier debugging and troubleshooting
- •Prevents data corruption
- •Better user experience
- •Reduced system complexity
Anti-Patterns to Avoid
- ×Silently ignoring errors
- ×Allowing invalid data to propagate
- ×Late error detection
Examples
Practical Tips
- 💡Validate inputs at system boundaries
- 💡Use assertions for internal consistency
- 💡Implement comprehensive monitoring
Related Principles:
Graceful Degradation
System should continue to operate with reduced functionality when components fail
When parts of a system fail, the remaining parts should continue to function, possibly with reduced capabilities.
Benefits
- •Better user experience during failures
- •Improved system availability
- •Reduced impact of partial failures
- •Better fault tolerance
Anti-Patterns to Avoid
- ×Complete system failure for minor issues
- ×No fallback mechanisms
- ×All-or-nothing functionality
Examples
Practical Tips
- 💡Identify critical vs non-critical features
- 💡Implement fallback mechanisms
- 💡Design for partial functionality
Related Principles:
Principle of Least Privilege
Grant only the minimum access rights necessary for users and processes
Every program and user should operate using the least set of privileges necessary to complete the job.
Benefits
- •Reduced attack surface
- •Limited blast radius of security breaches
- •Better compliance with security standards
- •Easier access management
Anti-Patterns to Avoid
- ×Admin access for regular operations
- ×Overly broad permissions
- ×Shared service accounts
Examples
Practical Tips
- 💡Regularly audit and review permissions
- 💡Use role-based access control
- 💡Implement just-in-time access
Related Principles:
Defense in Depth
Implement multiple layers of security controls
Use multiple security measures to protect information and systems, so if one layer fails, others continue to provide protection.
Benefits
- •Better protection against attacks
- •Reduced single points of failure
- •Compliance with security standards
- •Improved incident response
Anti-Patterns to Avoid
- ×Relying on single security measure
- ×Security as an afterthought
- ×Perimeter-only security
Examples
Practical Tips
- 💡Layer different types of security controls
- 💡Implement security at multiple levels
- 💡Regular security assessments
Related Principles:
Effective Caching Strategy
Cache data at appropriate levels to improve system performance
Implement caching at multiple levels (browser, CDN, application, database) to reduce latency and improve user experience.
Benefits
- •Reduced latency
- •Lower server load
- •Better user experience
- •Cost savings on infrastructure
Anti-Patterns to Avoid
- ×No caching strategy
- ×Cache invalidation problems
- ×Over-caching leading to stale data
Examples
Practical Tips
- 💡Cache at multiple levels
- 💡Implement proper cache invalidation
- 💡Monitor cache hit ratios
Related Principles:
Data Consistency
Ensure data remains accurate and consistent across the system
Maintain data integrity through proper transaction management, consistency models, and validation rules.
Benefits
- •Reliable business operations
- •Better user trust
- •Compliance with regulations
- •Easier debugging and maintenance
Anti-Patterns to Avoid
- ×Ignoring data consistency requirements
- ×No transaction management
- ×Inconsistent validation rules
Examples
Practical Tips
- 💡Choose appropriate consistency model
- 💡Implement proper validation
- 💡Use transactions for critical operations
Related Principles:
Design Principles Summary
Application Strategy: Start with Fundamental principles as they form the foundation of good system design. Important principles should be applied in most projects. Recommended principles provide additional value in specific contexts.