Previous-generation instances
Each new AWS generation usually delivers more performance for less money. Staying on the old one means paying more for the same work.
What this problem is
AWS releases new generations of instance families every few years — m5 after m4, m6i after m5, and so on. The newer generation almost always runs on better hardware and costs the same or less per vCPU. The result is that a previous-generation instance delivers less per dollar than its direct successor.
Nobody deliberately picks the old generation. What happens is that the instance type got fixed in a CloudFormation template, a Terraform module or an AMI, and started replicating itself. Every new machine is born with the type the template names, and the template was written when that was the current generation.
Migrating within the same x86 architecture is the safest upgrade on this list: no processor family change, no recompile, no operating system change. It requires stopping and starting the instance — restarting the database, on RDS — which means a maintenance window, and nothing more than that.
How we detect it
For EC2, we read spend by instance type from Cost Explorer with GetCostAndUsage. For RDS, we list instances with DescribeDBInstances. In both cases we compare the family in use against its same-architecture successor.
- Previous-generation EC2 instances
- Previous-generation RDS databases
What it costs
The gap between one generation and the next typically runs around 10% of the on-demand price, varying by family and region — and the newer generation normally delivers more performance at the lower figure.
Public AWS list prices, us-east-1, subject to change. The figure in your report is computed against your resources in your regions.
How it appears in the report
An illustrative example, with invented resources and figures. In the report each finding carries the real resource, its region, and the fix command where a safe one exists.
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