How does vertical scaling differ from horizontal scaling?

Vertical and horizontal scaling differ in how the system gets extra resources as load grows.

#Vertical scaling (Scale-Up)

Strengthening a single server:

• adding more RAM
• installing a more powerful CPU
• speeding up the disk

Upsides: simple to set up. Downsides: there's a physical ceiling, you can't "pump up" one server indefinitely.

#Horizontal scaling (Scale-Out)

Adding new servers to the system, to split data and load between them.

• several machines work together as a single store
• the cluster can be expanded almost indefinitely

Upsides: scales better and further. Downsides: the infrastructure is more complex.

#The difference, in one sentence

• vertical, making one machine stronger
• horizontal, adding many machines and splitting the load between them