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 means adding more servers.

Vertical scaling means giving each server more CPU, RAM, or disk.

2. Load Balancing

Distribute traffic across multiple servers.

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) fits when you need ACID guarantees, rich joins, and a strict schema you can reason about with the whole team.

NoSQL fits when you need flexible documents, easier horizontal scale-out, or very high write throughput, and you accept different consistency tradeoffs.

Replication

Key Components

Design Process

Start with these fundamentals and build from there!