System Design Basics: Building Scalable Applications

System design is crucial for building applications that can handle millions of users. Here are the fundamental concepts.

Core Principles

1. Scalability

**Horizontal Scaling:** Add more servers

**Vertical Scaling:** Increase server capacity

2. Load Balancing

Distribute traffic across multiple servers:

- **Round Robin:** Distribute sequentially

- **Least Connections:** Route to least busy server

- **IP Hash:** Route based on client IP

3. Caching

Store frequently accessed data in fast storage:

# Example: Redis caching
import redis

cache = redis.Redis()

def get_user(user_id):
    # Check cache first
    cached = cache.get(f"user:{user_id}")
    if cached:
        return json.loads(cached)
    
    # Fetch from database
    user = db.get_user(user_id)
    
    # Store in cache
    cache.setex(f"user:{user_id}", 3600, json.dumps(user))
    
    return user

Database Design

SQL vs NoSQL

SQL (Relational):

- ACID compliance

- Complex queries

- Structured data

NoSQL:

- Horizontal scaling

- Flexible schema

- High throughput

Replication

- **Master-Slave:** Read from replicas

- **Master-Master:** Write to any node

Key Components

1. **CDN:** Content delivery network for static assets

2. **Message Queue:** Async processing (RabbitMQ, Kafka)

3. **Microservices:** Decompose into services

4. **API Gateway:** Single entry point

Design Process

1. **Requirements:** Functional and non-functional

2. **Capacity Estimation:** Traffic, storage, bandwidth

3. **API Design:** Endpoints and data models

4. **Database Design:** Schema and partitioning

5. **Component Design:** High-level architecture

6. **Scaling:** Handle bottlenecks

Start with these fundamentals and build from there!