System Design Fundamentals

What is System Design?

System Design is the process of defining the architecture, components, modules, interfaces, and data for a system to satisfy specified requirements.

Key Concepts:

• Scalability - Ability to handle increased load
• Reliability - System operates correctly over time
• Availability - System is operational when needed
• Performance - Response time and throughput
• Maintainability - Easy to modify and extend

Part 1: System Architecture Patterns

Monolithic Architecture

Benefits:

• Simple to develop and deploy
• Easy to test and debug
• No network latency between components
• ACID transactions across all data

Drawbacks:

• Difficult to scale individual components
• Single point of failure
• Technology lock-in
• Deployment affects entire system

Monolithic Architecture Structure

Part 2: Scaling Concepts

Vertical vs Horizontal Scaling

Vertical Scaling:

• Add more power to existing server
• Simpler architecture
• Limited by hardware constraints
• Higher cost per unit of performance

Horizontal Scaling:

• Add more servers to the system
• Better fault tolerance
• More complex architecture
• Better cost efficiency at scale

Scaling Request Flow Comparison

Understanding how each scaling approach handles incoming requests is crucial for architectural decisions.

Scaling Trade-offs Comparison

Scaling Decision Flowchart

Scaling Architecture Comparison

Part 3: Key Metrics

Performance Metrics

Latency Percentiles:

• P50 (Median): 50% of requests
• P90: 90% of requests
• P95: 95% of requests
• P99: 99% of requests
• P99.9: 99.9% of requests

The Nines of Availability:

• 99% = 3.65 days downtime/year
• 99.9% = 8.76 hours downtime/year
• 99.99% = 52.56 minutes downtime/year
• 99.999% = 5.26 minutes downtime/year

Performance Metrics Visualization

Latency vs Throughput Relationship

Understanding how latency and throughput affect each other is critical for system performance optimization.

Availability vs Reliability Relationship

Understanding the difference between availability and reliability helps design systems that meet business requirements.

SLA/SLO/SLI Hierarchy and Relationships

Understanding the relationship between SLA, SLO, and SLI is crucial for defining and measuring system quality.

System Health Metric Flow

Understanding how all metrics flow together to indicate overall system health.

Part 4: Design Principles

Core Design Principles

Separation of Concerns:

• Each component has a single responsibility
• Clear boundaries between different concerns
• Easier to understand and maintain

Abstraction:

• Hide implementation details
• Provide clean interfaces
• Reduce complexity for users

Modularity:

• Break system into independent modules
• Each module can be developed separately
• Easier to test and debug

Loose Coupling:

• Minimize dependencies between components
• Changes in one component don't affect others
• More flexible and maintainable system

Layered Architecture Pattern

Understanding how to properly separate concerns through layered architecture is fundamental to system design.

Dependency Injection and Inversion

Understanding dependency management through dependency injection and inversion of control patterns.

Single Responsibility Principle

Understanding how to properly separate responsibilities to create maintainable and flexible systems.

Design Principles Architecture

This diagram visualizes the four fundamental design principles and how they create maintainable, scalable systems.

Part 5: Back-of-Envelope Calculations

Essential Numbers Every Engineer Should Know

Key Insights:

• Memory is 100x faster than SSD
• SSD is 100x faster than hard disk
• Network round-trip is VERY slow
• Avoid disk seeks in hot paths!

QPS Calculation Example

System Design Implications:

• Design for peak QPS, not average
• Read-heavy system (25:1 ratio)
• Need aggressive caching strategy
• Database read replicas required
• CDN for static content delivery

Storage Calculation Example

Storage Strategy Implications:

• Media dominates storage (99.925% vs 0.075% for text)
• Need different strategies for text vs media
• Text: Standard database with indexing
• Media: Object storage (S3) with CDN distribution
• Cost considerations: Media storage is the major cost factor

QPS Calculation Flow

Step-by-step process to calculate Queries Per Second (QPS) and determine the right architecture for your system.

Storage Calculation Flow

Step-by-step process to calculate storage requirements and choose the right storage strategy for your system.

Bandwidth Calculation Flow

Step-by-step process to calculate network bandwidth requirements and optimize data transfer costs.

System Design Calculations

Part 6: CAP Theorem

Understanding CAP Theorem

CAP Theorem states that in a distributed computer system, you can only guarantee two out of the following three properties:

• Consistency: All nodes see the same data simultaneously
• Availability: The system remains operational
• Partition Tolerance: The system continues despite network failures

CAP Theorem Venn Diagram

CAP Theorem Trade-offs in Depth

CAP Theorem Decision Flow

CAP Theorem Real-World Examples

Summary

Key Takeaways:

1. System Design is about making informed architectural decisions
2. Scalability can be vertical (scale up) or horizontal (scale out)
3. Performance metrics include latency, throughput, and availability
4. Design principles guide architectural decisions
5. CAP Theorem defines fundamental trade-offs in distributed systems
6. Back-of-envelope calculations help estimate system requirements

Next Steps:

• Practice with real-world examples
• Learn about specific technologies and patterns
• Understand trade-offs between different approaches
• Build systems and measure their performance
• Apply CAP theorem to design decisions

Remember: System design is an iterative process. Start simple, measure, and evolve based on real requirements and constraints.

Master the core concepts of system design. Learn about scalability, reliability, availability, and the fundamental principles that guide architectural decisions.