Horizontal scaling (Scaling in and Scaling out ) is flexible in a cloud situation as it allows you to run a large number of VMs to handle load.
Vertical scaling (Scaling up and Scaling down) keeps the number of resources constant, but gives those resources more capacity in terms of memory, CPU speed, disk space and network.
Vertical scaling (Scaling up and Scaling down) keeps the number of resources constant, but gives those resources more capacity in terms of memory, CPU speed, disk space and network.