Masst DocsWhat is System Design?
An introduction to system design, why it matters, and how it's used in building scalable software systems.
What is System Design?
System Design is the process of defining the architecture, components, modules, interfaces, and data flow of a system to satisfy specified requirements. It's about making high-level choices about how different parts of a system work together.
Why is System Design Important?
- Scalability: Design systems that handle growth—more users, more data, more requests.
- Reliability: Build systems that work correctly, even when things go wrong.
- Maintainability: Create systems that are easy to understand, modify, and extend.
- Performance: Ensure systems respond quickly and handle load efficiently.
Types of System Design
High-Level Design (HLD)
Focuses on the overall architecture:
- System components and their interactions
- Data flow between services
- Technology choices (databases, caching, messaging)
- Infrastructure decisions (cloud, load balancing, CDN)
Low-Level Design (LLD)
Focuses on implementation details:
- Class diagrams and object relationships
- API contracts and method signatures
- Database schemas
- Design patterns within components
Key Concepts to Master
| Concept | Description |
|---|---|
| Scalability | Ability to handle increased load |
| Availability | System uptime and accessibility |
| Consistency | Data accuracy across the system |
| Latency | Response time for requests |
| Throughput | Number of operations per unit time |
| Fault Tolerance | Handling failures gracefully |
System Design Interview Process
A typical system design interview follows these steps:
- Clarify Requirements: Understand functional and non-functional requirements
- Estimate Scale: Calculate expected load, storage, and bandwidth
- Define High-Level Design: Sketch the main components
- Deep Dive: Explore specific components in detail
- Identify Bottlenecks: Discuss trade-offs and optimizations
Real-World Example
Designing a URL Shortener:
- Functional: Shorten URLs, redirect to original
- Non-functional: Low latency, high availability
- Components: API servers, database, cache
- Scale: Millions of URLs, billions of redirects
Interview Tips
- Always clarify requirements before designing
- Think about scale from the start—millions of users, not hundreds
- Discuss trade-offs explicitly (CAP theorem, cost vs performance)
- Use real-world examples to support your design choices
- Don't forget about failure scenarios and how to handle them
System design is both an art and a science. The more systems you study, the better your intuition becomes for making the right architectural decisions.