A company's workloads frequently shift between instance families and AWS Regions as teams experiment with new architectures, but overall hourly compute spend is fairly predictable. They want a 1-year discount commitment that keeps working even as the specific instance types and Regions in use change, without reserving physical capacity in any particular Availability Zone. Which purchase option fits best?
- A Compute Savings Plan, which discounts EC2 (and Fargate/Lambda) usage regardless of instance family, size, OS, tenancy, or Region
- A zonal Reserved Instance, which reserves capacity in one Availability Zone for one specific instance type
- An On-Demand Capacity Reservation, since it can be created for any duration with no commitment
- A Dedicated Host reservation, since it guarantees the same discount across every instance family automatically
Why A? And why not the others?
Correct answer: A. A Compute Savings Plan, which discounts EC2 (and Fargate/Lambda) usage regardless of instance family, size, OS, tenancy, or Region
A Compute Savings Plan is a commitment to a fixed dollar amount of compute usage per hour for a 1- or 3-year term, and in exchange its discount automatically applies to EC2 usage regardless of instance family, instance size, operating system, tenancy, or Region, and even extends to AWS Fargate and Lambda usage, which is exactly the flexibility this company's shifting architecture needs; it also reserves no physical capacity, so the discount is never tied to any particular Availability Zone. A zonal Reserved Instance is the opposite fit: it reserves capacity for one specific instance type in one specific Availability Zone, so any change in instance family or Region breaks the match and forfeits the discount unless the Reserved Instance is separately modified or exchanged. An On-Demand Capacity Reservation guarantees available capacity rather than providing a billing discount, so despite its flexible term it does not address the stated one-year discount requirement at all. A Dedicated Host reservation is a hardware tenancy construct aimed at licensing and compliance needs, and it carries no automatic cross-family billing discount comparable to a Savings Plan.
Source: AWS documentation: Savings Plans — Compute Savings Plans vs Reserved Instances