In our experience, if your EC2 got resource left for a period of time, lets say 1-2 months, even AWS say it is not, but we always experience performance drop. For example: server response time drop from 400ms to 600ms . Or CPU raised from 40% to 70% in average.
In many case, many users will not 100% * 24 * 7 consume their server resources. So, in my experience, AWS want to reduce cost and reallocate some resource privately to other clients. If your server is actually low utilization, it is OK. But, in my situation, we need high response time and we reserve the CPU for that. We will feel performance drop.
How we deal with that ? That is what auto-scaling group should do. If in your auto-scaling group, your server will keep renew itself. Like turning off old servers and start new servers, the EC2 resource allocation will maintain at best performance.
Such issue especially obvious in Drupal. Drupal PHP request involve in many hooks / functions / third party calls etc. Server CPU requirement is higher than other web PHP applications. So, renewing server can help to keep better performance.
How to deploy auto-scaling group ? Call BootDev 🙂
Hope above information can help anyone that feel AWS sometimes drop performance by time 🙂