Difference between horizontally scaling and vertically scaling

 Horizontal scaling means that you scale by adding more ec2 machines into your pool of resources whereas Vertical scaling means that you scale by adding more power (CPU, RAM) to an existing ec2 machine.

Vertical Scaling usually means upgrade of server hardware.

Horizontal Scaling is adding more ec2 machines.

With horizontal-scaling it is often easier to scale dynamically by adding more machines into the existing pool — Vertical-scaling is often limited to the capacity of a single machine, scaling beyond that capacity often involves downtime and comes with an upper limit.

Good examples of horizontal scaling are Redis, MongoDB.

Good example of vertical scaling is MySQL — Amazon RDS (The cloud version of MySQL).

Source : https://medium.com/@khushalbisht/aws-scaling-horizontally-vs-vertically-3e30e3e71118