What is the difference between horizontal and vertical scaling?

Question

Accepted Answer

**Horizontal** — add more machines. **Vertical** — add more power.

**Horizontal Scaling:**
- Add more servers.
- Load balancer distributes.
- Linear cost.
- Better fault tolerance.

```
Horizontal:
[Server 1] [Server 2] [Server 3]
  (Multiple servers)
  (Distributed load)
```

**Vertical Scaling:**
- Upgrade existing server.
- Add CPU, RAM.
- Limited by hardware.
- Single point of failure.

```
Vertical:
[Server: 4 CPU → 8 CPU → 16 CPU]
  (More powerful)
  (Single server)
```

**Key differences:**
- **Horizontal** — more servers.
- **Vertical** — more power.
- **Horizontal** — better scalability.
- **Vertical** — simpler.

Systems Analyst: What is the difference between horizontal and vertical scaling?