Definition
System Design is the process of defining the architecture, components, and interfaces of a system to satisfy specified requirements.
Think of it like: Designing a city. You need to plan roads (network), buildings (servers), utilities (databases), and services (applications) to support millions of people (users) efficiently and reliably.
Core Goals of System Design
Scalability
Handle growing users and data
Example: Instagram: 1B+ users, 100M+ photos/day
Reliability
System works when you need it
Example: Banking: 99.99% uptime (4min downtime/month)
Performance
Fast response times
Example: Google Search: <100ms average response
Security
Protect user data and privacy
Example: WhatsApp: End-to-end encryption
Scale Complexity
Why System Design Matters
Good Design
- • WhatsApp: 55 engineers supporting 2B users
- • Instagram: Sold to Facebook for $1B with 13 employees
- • Zoom: Handled 10x traffic during COVID without major issues
Poor Design
- • HealthCare.gov: $2B spent, failed launch
- • Knight Capital: $440M lost in 45 minutes due to bad deployment
- • Pokémon GO: Crashed on launch day, lost millions of users
Common System Design Questions
Scale horizontally (more servers), add caching, optimize database queries, use CDNs.
Database replication, backup strategies, failover mechanisms, health checks.
Caching layers, async processing, database indexing, code optimization.
ACID transactions, eventual consistency, conflict resolution, distributed locking.
Key Takeaways
- • System design is about making trade-offs between competing requirements
- • Start simple, scale when needed (don't over-engineer early)
- • Every architectural decision has pros and cons
- • Focus on the most critical requirements first
- • Learn from real-world systems and failures