Cloud cost
Rightsizing
Matching a resource's provisioned size to its actual, observed utilization instead of the peak it was originally sized for.
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Definition
Rightsizing means comparing what an instance, volume, or database is provisioned for against what it uses in practice (CPU, memory, IOPS, throughput) over a representative window, then resizing down (or, occasionally, up) to match. Most fleets carry meaningful oversizing simply because instances get sized once, for a traffic peak or a worst-case estimate, and are rarely revisited once the peak passes or the workload matures.
It's a recurring practice, not a one-time project: utilization drifts as code, traffic, and dependencies change, so a resource that was correctly sized six months ago can easily be oversized today.
Where it shows up
Rightsizing draws on a resource's utilization metrics: CPU, memory, IOPS, or throughput, tracked over a representative window in a monitoring console or the provider's own recommendations tool, such as AWS Compute Optimizer. The provisioned size sits on the same resource record as the observed usage the recommendation compares it against.
What makes it expensive
This gets expensive fast: sizing an instance once for a traffic peak and never revisiting it as the workload matures. The peak passes, the traffic pattern settles, the dependencies change, and the instance stays exactly the size somebody guessed at on launch day. The utilization data has been sitting there the whole time, and nothing ever prompts anyone to open it.
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