How to rightsize without breaking production
The Lizrd team · · 2 min read
Rightsizing — matching a resource’s size to its real usage — is the single most reliable way to cut a cloud bill. It’s also where teams get nervous, because “make it smaller” and “keep it up” feel like they’re in tension.
They don’t have to be. Done with evidence and a rollback, rightsizing is boring in the best way. Here’s the approach.
Start from usage, not intuition
The instinct is to reason about what a service “should” need. Don’t. Pull the actual numbers: 30-day CPU and memory, peaks included. A checkout API sitting at 18% CPU and 24% memory on a 1-vCPU/2-GB task isn’t a judgment call — it’s over-provisioned by the data.
The rule of thumb: size for the peak plus healthy headroom, not for a worst case that never happens.
Change one variable, keep a rollback
Rightsizing goes wrong when it becomes a redesign. It shouldn’t. The safe version is a single, reversible change:
- instance_type = "m6g.2xlarge"
+ instance_type = "m6g.xlarge"
One line. Applied through your normal pipeline. Trivial to revert if the numbers say so. If you can’t roll it back in one step, it’s too big a change to call “rightsizing.”
Prioritize by impact, not by ease
Not all savings are equal. A Graviton migration on a large fleet can dwarf a dozen small tweaks. Rank candidates by dollars-at-stake × confidence, and work top-down — you’ll capture most of the savings in the first handful of changes.
Verify it actually landed
The step everyone skips: confirm the bill moved. An estimated saving that never shows up is worse than no saving, because you’ve already spent the credibility. Compare the realized number against the estimate and close the loop — this is what separates real FinOps from optimistic math.
Make it repeatable
Rightsizing isn’t a one-time cleanup; workloads drift and it comes back. The teams that stay lean treat it as continuous — which is exactly why we built Lizrd to find, propose, and validate these changes on an ongoing basis, read-only, with the exact diff every time.
Small, evidenced, reversible, verified. That’s how you rightsize without holding your breath.