AWS Tools for Rightsizing Instances
To start off, here is a quick and dirty summary and comparison among the 3 tools:
Generally, Compute Optimizer (CO) is the best, but note that because it doesn’t consider the usage of Reserve Instances coverage, there can be instances where CO recommends you to right size it, but because the instance is already under RI, there is $0 savings involved. So the recommended way is to use CO and Cost Explorer Rightsizing Recommendations together!
Here are a bit more information on each of them:
AWS Compute Optimizer. This AWS feature creates an automated report that analyzes your compute resources and comes up with recommendations for EC2 instance size optimizations.
AWS Cost Explorer Rightsizing Recommendations. Nested within Cost Explorer, this is a tool that you can potentially utilize with ease.
AWS Trusted Advisor. This AWS service executes periodic checks on your AWS infrastructure and comes up with a list of recommendations. There is a section for Cost Optimizations, which typically contains useful findings, such as idle or under-utilized resources, among others. Do note that in order to access these findings, you have to enable AWS Support, which has a cost depending on the plan you choose (e.g. Developer, Business or Enterprise).
Caveats/Notes when doing rightsizing:
- It might be difficult to right-size some older apps might not run correctly under different hardware architecture, or need different drivers, or not be supported by the application vendor
- Some resources should be “oversized” e.g. disaster recovery instances
- Other Right sizing technical considerations: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-resize.html