Scalability: Vertical vs Horizontal Scaling

What is Scalability?

Scalability is a system's ability to handle increased load by adding resources without degrading performance.

Vertical Scaling (Scale Up)

Add more power to your existing machine — more CPU, RAM, faster storage.

Pros: Simple, no code changes, works well for databases

Cons: Hard ceiling, single point of failure, expensive at high end

Horizontal Scaling (Scale Out)

Add more machines and distribute load across them.

Pros: No hard ceiling, high availability, commodity hardware

Cons: Complexity, shared state management, network latency

Stateless vs Stateful Scaling

Database Scaling Options

Real-World Scaling Journey

Key Takeaway

Start vertical. Scale horizontal when you need availability or hit vertical limits.