One of my clients a couple of years ago was running a legacy LAMP stack on m5a instances, routinely maxing out the CPUs and bleeding serious money every month.

One of my clients a couple of years ago was running a legacy LAMP stack on m5a instances, routinely maxing out the CPUs and bleeding serious money every month. Moved them over to c6i instances with the same number of cores, and CPU utilization dropped by 60%. Lesson: think long and hard before you tie yourself down with multi-year saving plans restricted to an older generation of CPUs.