Reserved Instances Optimization Guide

Reserved Instances (AWS), Reservations (Azure), and Committed Use Discounts (GCP) are the single biggest lever for cutting the 비용 of steady-state 클라우드 워크로드s. A 1-year commitment typically saves 30 to 40 percent off on-demand, and a 3-year commitment saves 50 to 72 percent — savings that, for a 워크로드 spending $10,000 per month, can free up $36,000 to $86,000 per year.

What Is a Reserved Instance?

A Reserved Instance (RI) is not a separate 인스턴스 type — it is a billing 할인 applied to on-demand usage that matches the reservation’s specifications. You continue to launch the same VM you always have; the 클라우드 프로바이더’s billing system applies the 할인ed rate to the matching hours of usage. Unused reservations do not roll over, so the goal is to size the commitment to your baseline usage, not your peak.

The Three Commitment Horizons

The 1-year No Upfront option is the safest starting point: no cash outlay, and the commitment can be exchanged within the 인스턴스 family if your 워크로드 changes. Move to 3-year All Upfront only for 워크로드s you are certain will run unchanged for the full term, since the break-even point is typically 12 to 15 months.

How to Stagger Reservations

A common mistake is to commit the entire fleet on the same start date, which forces an all-or-nothing renewal 12 or 36 months later. Instead, stagger reservations:

1. Month 1 — commit 30 percent of baseline usage as a 1-year reservation.
2. Month 2 — commit another 30 percent, again 1-year.
3. Month 3 — commit the final 30 to 40 percent.

After 12 months you are renewing one-third of your reservations each month rather than the whole fleet, which gives you room to right-size, switch 인스턴스 families, or migrate 프로바이더s without stranding committed spend.

Savings Plans vs Reserved Instances

On AWS and Azure, the modern alternative to RI is a Savings Plan (AWS) or Savings Plan (Azure). A Savings Plan commits to a dollar-per-hour spend rather than a specific 인스턴스 family, so the 할인 applies across any 인스턴스 size or family in the committed 리전. The 할인 is slightly lower (up to 66 percent on AWS Compute Savings Plans vs 72 percent on RIs), but the flexibility is worth it for teams whose 인스턴스 mix changes over time.

GCP Committed Use Discounts

GCP works differently. Sustained-Use Discounts (SUDs) apply automatically when a VM runs more than 25 percent of the month, with the 할인 scaling up to 30 percent off at 100 percent utilization — no commitment required. Committed Use Discounts (CUDs) stack on top of SUDs for an additional 21 to 57 percent off, and GCP’s CUDs are unique in that they apply to vCPU and memory independently, so you can commit CPU without committing memory.

Common Mistakes to Avoid

• Over-committing — committing more than your baseline leaves you paying for unused hours. Always commit to the 30-day average, not the peak.
• Ignoring convertible RIs — AWS Convertible RIs 비용 slightly more but can be exchanged for a different 인스턴스 family, 리전, or operating system at no penalty.
• Forgetting RI expiration — set calendar reminders 30 days before each reservation expires, so you can renew or downsize before the 할인 lapses.
• Mixing 스팟 and RI for the same 인스턴스 — if part of your 워크로드 runs on 스팟, do not also reserve the same 인스턴스 type; the RI 할인 is wasted when the 인스턴스 is on 스팟.

See our AWS vs Azure 컴퓨트 비교 for the specific per-인스턴스 reservation savings, and the 비용 optimization 가이드s overview for the next layer of savings.