Which Use Case Best Fits EC2 On-Demand Instances?
For which use case are Amazon EC2 On-Demand Instances MOST cost-effective?
Community Votes
100% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
The question tests whether you can distinguish On-Demand from Spot and Reserved/Savings Plans pricing by workload length and fault tolerance; the trap is picking the restartable transcoding job, which actually favors Spot Instances.
Amazon EC2 pricing models are matched to workload duration and flexibility, and On-Demand Instances shine where no commitment or interruption tolerance applies. This page shows that a one-month quality assurance test is the use case where On-Demand is most cost-effective.
Option A is the most common wrong pick because learners equate 'short-term or flexible' with On-Demand, but a compute-intensive job that can be restarted is the textbook Spot Instances case, where interruptions are acceptable for deep discounts.
Community Discussion (4 comments)
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Expert Analysis
Why the Answer Is Correct
Option B describes an instance running continuously for only one month for quality assurance tests, a duration shorter than the one-year minimum commitment required by Standard Reserved Instances and most Savings Plans. Because no long-term commitment can be purchased for a 30-day window, On-Demand pricing — billed per second or hour with no upfront fee and no termination penalty — is the lowest-cost way to run that workload. On-Demand also fits short-term, unpredictable needs where you cannot accurately forecast demand, exactly as AWS documents for this pricing model.Why the Other Options Are Wrong
Option A describes compute-intensive video transcoding that can be restarted, which is the canonical fault-tolerant, flexible workload that Spot Instances serve at discounts of up to 90% compared with On-Demand. Option C's web server running for a full year is a steady-state workload where a one-year Reserved Instance or Savings Plan would cost less than On-Demand rates. Option D's database running three years is the clearest Reserved Instances case, where a three-year Standard RI (or Compute Savings Plan) yields the largest effective discount.Community Comment Notes
The community vote was unanimous for B, with a77c459 explaining that 'B looks like the right answer as it's shorter than the time required for the reserved instances like 1 year or 3 years,' which is exactly the correct reasoning about commitment terms. Kilobay1 dissented toward A, arguing that On-Demand suits workloads where 'the workload is unpredictable or short-term,' but overlooked that a restartable transcoding job explicitly signals Spot tolerance rather than On-Demand necessity. ShaiTay and d00b229 independently restated option B as the instance used for one month of quality assurance testing, aligning with the AWS pricing guidance.Official Reference
Exam Strategy
Read the workload duration and the words 'can be restarted' first: restartable or interruptible means Spot, one-to-three-year steady state means Reserved or Savings Plans, and anything under a year with no commitment means On-Demand.
Frequently Asked Questions
Why is restartable video transcoding not the best On-Demand use case?
Because it is fault-tolerant and flexible, Spot Instances deliver up to 90% off On-Demand pricing; interruptions are acceptable when the job can be restarted.
Why don't Reserved Instances beat On-Demand for the one-month QA test?
Standard Reserved Instances and most Savings Plans require a one-year or three-year term, so a 30-day workload cannot use them and On-Demand is cheapest.
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