What is the difference between scale-out and scale-up?
Scaling Out refers to adding resources. e.g. Moving from 1 server to 3 servers.
Scaling Up refers to improving existing resources. e.g. Moving from 1 small server to 1 large server.
Scaling out is synonymous with horizontal scaling. Adding whole systems to grow the total resource pool.
Scaling up is synonymous with vertical scaling. Adding components like CPU, RAM, Disk, or I/O.