Savings Plans and Convertible Reserved Instances

When comparing 1-year Savings Plans and Convertible Reserved Instances (RIs), there are several key differences to consider:

Flexibility and Pricing: Savings Plans generally offer more flexibility than Convertible RIs. With Savings Plans, you commit to a consistent amount of compute usage (measured in $/hour) for a 1-year term. This allows you to automatically benefit from the discounted rates across a wide range of services and instance types without manual intervention.

Convertible RIs, while more flexible than Standard RIs, still require manual exchanges when you want to modify instance attributes. They offer discounts of up to 66% off On-Demand pricing, which is comparable to Savings Plans.

Cross-family and Regional Flexibility: Compute Savings Plans provide the highest level of flexibility. They allow you to change instance families, sizes, and even move across regions without any manual intervention. This flexibility extends to EC2, Fargate, and Lambda services.

Convertible RIs do offer some flexibility to change instance family, size, OS, tenancy, and region. However, these changes require manual exchanges, which could potentially lead to some administrative overhead.

Suitability for Dynamic Workloads: For dynamic workloads over a 1-year term, Compute Savings Plans are generally more suitable. They automatically apply to your usage regardless of instance family, size, Availability Zone, region, operating system, or tenancy. This means you can freely adjust your infrastructure to meet changing demands without losing your discount benefits.

Convertible RIs, while offering some flexibility, may not be as convenient for highly dynamic workloads due to the need for manual exchanges when making significant changes.

In summary, if you anticipate needing to frequently adjust your instance types, move between regions, or want the flexibility to use different compute services (EC2, Fargate, Lambda), a Compute Savings Plan would likely be more suitable for your dynamic workloads over a 1-year term. It offers greater flexibility and ease of use compared to Convertible RIs, while still providing significant cost savings.

Sources
EC2 Instance Savings Plan VS Flexible reserved instance | AWS re:Post
Savings Plan and Reserved Instances | AWS re:Post
Main Differences b/t EC2 Saving Plans (Compute and Instance) and Reserved Instances | AWS re:Post