How to Right-Size Your AWS Infrastructure Without Hurting Performance

How to Right-Size Your AWS Infrastructure Without Hurting Performance

Right-sizing is the process of matching cloud resource allocation to actual workload requirements. It is one of the highest-impact cost optimisation actions available to AWS teams, and one of the most commonly deferred because it involves risk of performance degradation if done incorrectly.

This guide covers how to approach right-sizing systematically and safely.

Collect Baseline Metrics First

Do not make sizing decisions based on intuition. Collect CloudWatch metrics for at least 30 days — ideally 60 to 90 — to capture normal traffic variation including end-of-month spikes, weekly patterns, and any seasonal variation.

For EC2, the relevant metrics are CPU utilisation, network in/out, disk read/write, and memory utilisation (if you have the CloudWatch agent installed). For RDS, track CPU, free memory, read/write IOPS, and connection count.

AWS Compute Optimizer analyses these metrics and produces specific recommendations with projected performance risk. Use it as a starting point, not a final answer.

Start With Non-Production Workloads

Right-sizing changes carry some risk, even small ones. Start with development and staging environments where a performance issue has lower business impact. This builds team confidence in the process and establishes a testing methodology before changes go near production.

The Two-Step Approach for Production

For production workloads, use a two-step approach: first reduce to an intermediate size, monitor for two to four weeks, then reduce further if metrics support it. Moving directly from an oversized instance to the minimum recommended size increases the risk of a performance incident. Incremental changes are reversible with minimal disruption.

Watch for Memory Constraints

CPU utilisation is easy to measure. Memory pressure is harder to detect without the CloudWatch agent installed on EC2 instances. Before downsizing an instance, install the agent and capture memory metrics for at least two weeks. An instance that appears underutilised on CPU metrics may be running close to memory limits.

Savings Plans and Reserved Instances After Right-Sizing

Right-size before committing to Reserved Instances or Savings Plans. If you purchase a one-year Savings Plan based on your current oversized instance types and then right-size, you have committed to paying for capacity you no longer need. Right-size first, stabilise, then commit.

Cloudain Perspective

Cloudain's cloud cost optimisation work includes structured right-sizing with metric analysis, staged rollout plans, and performance validation. If you want to reduce your compute costs without risking service degradation, we can build a right-sizing plan for your environment.