EC2 instance rightsizing savings

EC2 rightsizing — the easy 30-50% bill cut

Most production EC2 fleets run at 15-30% average CPU utilization. The remaining capacity is paid-for slack. Rightsizing brings utilization to 50-65% (still safe) and cuts spend 30-60% per instance.

The two-step move

1. Rightsize — analyze CloudWatch metrics, downsize over-provisioned instances
2. Cover with Savings Plans — Compute Savings Plans (1-yr or 3-yr commit) on the right-sized baseline

Default scenario: 12 instances × $280/mo × 12 = $40,320/yr. Rightsizing 50% × 80% of fleet = $16k savings. Layer Savings Plan on remaining = $8.5k more. Total annual savings: ~$24,500.

Where rightsizing is dangerous

• Burst workloads: instances that spike during peak need headroom. Average CPU misleads. Look at p99.
• Memory-bound apps: CPU utilization is irrelevant. Switch to memory-optimized rather than smaller.
• Network-bound apps: smaller instances = lower bandwidth caps. Verify network requirements.
• Database instances: never rightsize aggressively. Memory + connection limits scale with size.

Savings Plan vs Reserved Instance

Compute Savings Plans are strictly better than RIs for most workloads:

• Cover any instance family (vs RI which is family-locked)
• Cover Lambda + Fargate too (RIs only cover EC2)
• Match-rate flexibility (RIs require exact match)

Use RIs only for very stable, single-family workloads where the slight discount edge matters.

The 3-year math

3-year All-Upfront Savings Plan = ~50-55% off on-demand. If your usage is stable, this saves 18-22% over 1-yr No-Upfront. Cash up-front is the trade-off; capital-constrained startups stick with 1-yr.