Scaling vertically takes place through an increase in the specifications of an individual
resource (e.g., upgrading a server with a larger hard drive or a faster CPU). On Amazon EC2,
this can easily be achieved by stopping an instance and resizing it to an instance type that
has more RAM, CPU, IO, or networking capabilities
Scaling horizontally takes place through an increase in the number of resources (e.g.,
adding more hard drives to a storage array or adding more servers to support an application)