Service comparisons / Savings Plans vs Reserved Instances vs Spot Instances
Savings Plans vs Reserved Instances vs Spot Instances
Savings Plans and Reserved Instances cut prices for steady use in exchange for a one- or three-year commitment; Spot Instances use spare capacity at up to 90% off but can be interrupted. How to pick the right EC2 pricing option.
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| Question | Savings Plans | Reserved Instances | Spot Instances |
|---|---|---|---|
| Use it when | Steady compute spend you can commit to, while instance types may change | Steady use of a specific instance type, or a database or cache that needs it | Work that can stop and restart, such as batch, CI, rendering and stateless web tiers |
| Commitment | A dollar amount per hour for 1 or 3 years | A specific configuration for 1 or 3 years | None |
| Discount | Up to 72% (EC2 Instance Savings Plans); up to 66% (Compute Savings Plans) | Up to 72% (Standard); up to 66% (Convertible) | Up to 90% |
| Covers | Compute plans cover EC2, Fargate and Lambda in any Region | EC2, and also RDS, ElastiCache, OpenSearch and Redshift | EC2 (and Fargate Spot) |
| Watch out for | A commitment you don't use is still billed | Only zonal Reserved Instances reserve capacity | Instances can be reclaimed with a two-minute warning |
On-Demand is the default: no commitment and the full price. Every other option trades flexibility for a discount, so the right answer depends on how steady and how interruptible the workload is.
How to choose
- Steady 24/7 baseline, but the team may change instance families or move to containers: Compute Savings Plans.
- Steady use of one instance family in one Region: EC2 Instance Savings Plans or Standard Reserved Instances for the deepest discount.
- Databases and caches running all year: Reserved Instances for RDS or ElastiCache, or the newer Database Savings Plans.
- Fault-tolerant batch work, or extra capacity in an Auto Scaling group: Spot Instances, ideally across several instance types.
- Short or unpredictable work that can’t be interrupted: On-Demand.
- Guaranteed capacity for an event, with no long commitment: On-Demand Capacity Reservations.
Exam traps
- The cheapest answer that breaks a requirement is wrong. Spot is never right for “must not be interrupted”.
- A common best answer mixes options: Savings Plans for the baseline, Spot for scalable extra capacity, On-Demand for the rest.
- With AWS Organizations, discounts are shared across accounts on consolidated billing by default.