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Difficulty: MediumAWS Pricing Models

A financial services firm runs a risk-assessment analysis every Friday night. The analysis requires high-performance Amazon EC2 instances to run continuously for 6 hours. The process cannot be interrupted, as a single failure requires restarting the entire analysis from the beginning. Which EC2 purchasing option is the most cost-effective for this workload?

  1. On-Demand InstancesAnswer
  2. B
    Spot Instances
  3. C
    Reserved Instances
  4. D
    Dedicated Hosts

Answer

On-Demand Instances
On-Demand Instances are the correct choice because they offer a pay-as-you-go model with no long-term commitment or upfront payment. Since the workload only runs for 6 hours a week and cannot tolerate interruptions, paying exclusively for those 6 hours of guaranteed computing time is the most economical option.

Step-by-Step Solution

1
Analyze the workload characteristics: it runs for a short duration (6 hours once a week), is periodic, and cannot tolerate any interruptions.
Workload is classified as short-term, low-utilization (6 out of 168 hours per week), and interruption-intolerant.
This rules out Spot Instances (due to interruption risk) and indicates that constant-running options (Reserved Instances or Savings Plans) may be wasteful.
2
Evaluate the financial commitment of Reserved Instances versus On-Demand pricing.
On-Demand charges only for the 6 hours of weekly use, whereas Reserved Instances charge for all 168 hours of the week regardless of usage.
A 1-year or 3-year commitment is not cost-effective for a workload running only ~3.5% of the time.
3
Determine the best option among all available models.
On-Demand Instances provide the necessary reliability without the overhead of long-term commitment costs.
It offers the lowest total cost of ownership while fully meeting the application's stability requirements.

Key Concept

Selecting the most cost-effective EC2 purchasing option based on workload duration, pattern, and fault tolerance.
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Topics

AWS Pricing Models

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