AWS Compute Optimizer vs Cost Explorer: what is the difference?

Start with Cost Explorer when the bill is the question

Cost Explorer helps investigate spend by account, region, service, tag, and time. Use it when a team needs to understand where an EC2 increase came from, which environment is expensive, or which workloads should be reviewed first.

Use Compute Optimizer when resource shape is the question

Compute Optimizer analyzes configuration and utilization metrics to make rightsizing recommendations for eligible resources. For EC2, it can identify instances that look over-provisioned or under-provisioned and suggest options to assess.

A recommendation is still a review item. Memory use, latency, licensing, burst behavior, and operational risk can matter even when the charts look straightforward.

Use them together

Use Cost Explorer to find the spend worth investigating. Use Compute Optimizer to evaluate a running resource that may be the wrong size. For development and staging resources that do not need to run continuously, scheduling is a separate decision.

Continue with the AWS EC2 rightsizing guide, EC2 cost optimization tools, and EC2 scheduling guide.

Follow a simple review sequence

Start broad and narrow the work. In Cost Explorer, compare the recent period with the one before it. Group by service first, then by account, region, or tag until the change points to a small enough set of resources. A small one-off change does not need the same attention as a persistent increase in a shared environment, so sort the review list by impact and urgency.

For a shortlisted EC2 workload, read the Compute Optimizer recommendation alongside application context. Check whether the instance is customer-facing, whether it runs a batch job, and whether it has a known traffic peak. An instance can look quiet in an average chart and still need capacity for a short, important window.

Then choose one action. You may test a smaller size, move to another family, leave the resource alone, or schedule it outside team hours. The useful output is an owner and a next step, not a long list of recommendations.

Where the tools stop

Neither tool knows every operational constraint. Cost Explorer cannot tell whether a cost increase is intentional. Compute Optimizer cannot know that a short memory spike happens during a month-end process, that a licence is tied to a particular configuration, or that an application has no safe maintenance window.

Treat a recommendation as evidence, not an automatic change. The workload owner still needs to check application health, dependencies, maintenance constraints, and rollback options. The billing view and the engineering view belong in the same review.

Avoid the common shortcuts

Do not use one low CPU number as a resizing decision. CPU is one signal. Memory pressure, network throughput, disk I/O, queue depth, and the busiest interval matter too. Do not turn a recommendation into a production change without a clear revert path.

Also, do not expect rightsizing to solve the cost of an environment that is simply left on when nobody uses it. A development or staging resource can be correctly sized and still create waste because it runs nights and weekends. In that case, a reviewed schedule may be the cleaner lever.

Frequently asked questions

Do I need both tools?

They work well together, but they do different jobs. Cost Explorer helps find the part of the bill worth investigating. Compute Optimizer helps assess certain resources after that investigation.

Does a rightsizing recommendation mean the change is safe?

No. Review the workload and test a low-risk change first. A recommendation cannot replace knowledge of the application or its operational requirements.

What if the resource is only needed in office hours?

Sizing and operating hours are separate decisions. Keep the size that lets the workload work, then consider a reviewed schedule for eligible non-production resources.