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

	Vertical	Horizontal
Complexity	Low	High
Cost at scale	High	Lower
Availability	Low (SPOF)	High
Limit	Hard ceiling	Virtually unlimited

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