Which Amazon EC2 pricing option allows customers to bid for unused EC2 capacity with potential savings of up to 90%, while accepting that instances may be interrupted?
Spot Instances are the correct answer because they let you use AWS's spare EC2 capacity at discounts reaching up to 90%, with the critical trade-off that AWS can reclaim the instance with only a two-minute notice when that capacity is needed elsewhere. This makes them ideal for stateless, fault-tolerant, or flexible workloads, but you must design applications to handle sudden interruptions—exactly the behavior the question is testing.
Why this answer
Spot Instances allow customers to bid for unused EC2 capacity, offering potential savings of up to 90% compared to On-Demand pricing. However, these instances can be interrupted (terminated or hibernated) by AWS when the Spot price exceeds the customer's bid or when capacity is needed for On-Demand or Reserved Instance customers, making them ideal for fault-tolerant and flexible workloads.
Exam trap
The trap here is that candidates may confuse Spot Instances with Reserved Instances, thinking both offer similar discounts, but Reserved Instances require a commitment and are not interruptible, while Spot Instances are interruptible and involve bidding on unused capacity.
How to eliminate wrong answers
Option A is wrong because On-Demand Instances provide full pricing flexibility with no interruption risk, but they do not allow bidding on unused capacity or offer up to 90% savings. Option B is wrong because Reserved Instances provide a significant discount (up to 72%) in exchange for a 1- or 3-year commitment, but they are not interruptible and do not involve bidding on unused capacity. Option D is wrong because Dedicated Instances run on single-tenant hardware and are not associated with bidding on unused capacity or interruption; they are used for compliance or licensing requirements, not for cost savings via spot pricing.