Vertical scalability pertains to adding resources to individual server machines, for example, adding additional CPUs. Each machine is scaled to handle a certain load. In general, you might decide upon vertical scalability in your deployment because you have resource limitations or you are unable to purchase additional hardware as your deployment grows.
To vertically scale your deployment, you need to:
Size each messaging component
Test the load of a prototype of your system
Monitor system performance and adjust the deployment accordingly