A company runs Amazon EC2 instances in a research lab. The instances run for 3 hours each week and cannot be interrupted. What is the MOST cost-effective instance purchasing option to meet these requi

Question

Options

• ACompute Savings Plan
• BOn-Demand Instances
• CConvertible Reserved Instances
• DSpot Instances

• A
  9% (4)
• B
  70% (31)
• C
  16% (7)
• D
  5% (2)

Explanation

On-Demand Instances are the most cost-effective choice here because the workload runs for only 3 hours per week (roughly 156 hours per year), making any long-term commitment financially wasteful - you'd be paying for reserved capacity you almost never use.

Why the distractors are wrong:

• Compute Savings Plans (A) and Convertible Reserved Instances (C) both require a 1- or 3-year commitment, which only pays off when instances run consistently for hundreds or thousands of hours - not just 3 hours per week.
• Spot Instances (D) can be interrupted at any time, which directly violates the requirement that workloads cannot be interrupted.

Memory Tip: Think of the "break-even rule" - Reserved Instances and Savings Plans only save money if you run instances frequently enough to recoup the upfront commitment. If usage is very low (like a few hours per week), On-Demand wins because you pay only for what you use with no strings attached. Spot = cheap but interruptible; Reserved/Savings = cheap but requires heavy, consistent usage.

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