4.1 - AWS pricing models and purchase options
AWS Certified Cloud Practitioner objective 4.1 covers EC2 purchase options and how to match them to workloads. On-Demand instances have no commitment and cost the most per hour, best for short-term or unpredictable workloads. Reserved Instances or Savings Plans offer the largest discount in exchange for a one- or three-year usage commitment, best for a steady workload that runs 24/7 all year. Spot Instances use spare capacity for up to about 90% savings but can be interrupted by AWS with little notice, so they suit fault-tolerant, restartable jobs like batch image processing. There is also Dedicated Hosts for compliance. AWS Cost Anomaly Detection uses machine learning to flag unusual spend automatically. Expect scenario questions that describe a usage pattern - steady, unpredictable, or interruptible - and ask which EC2 purchase option minimises cost while meeting the workload's needs.
No commitment, unpredictable = On-Demand. Steady 24/7 all year, 1-3 year commit = Reserved / Savings Plans. Up to ~90% off but interruptible = Spot (fault-tolerant jobs). ML flags odd spend = Cost Anomaly Detection.
Practice questions
1. Which EC2 purchasing option offers the largest discount for a steady 1- or 3-year commitment?
- On-Demand Instances
- Spot Instances
- Reserved Instances / Savings Plans (correct answer)
- Dedicated Hosts on demand
Reserved Instances and Savings Plans give big discounts vs On-Demand for a 1- or 3-year commitment. Spot is cheapest but can be interrupted; On-Demand is flexible but priciest.
2. A batch job can be interrupted and restarted at any time and must cost as little as possible. Which EC2 purchasing option fits best?
- On-Demand Instances
- Reserved Instances
- Spot Instances (correct answer)
- Dedicated Hosts
Spot Instances use spare capacity at up to ~90% off but can be reclaimed with short notice, which suits fault-tolerant, interruptible workloads like batch jobs.
3. Which correctly distinguishes On-Demand, Reserved Instances, Spot, and Savings Plans?
- Spot is the most expensive with the strongest guarantee
- Reserved Instances have no discount over On-Demand
- On-Demand=pay-per-use no commitment; Reserved/Savings Plans=discount for 1-3yr commitment; Spot=deep discount, interruptible (correct answer)
- All four cost exactly the same
On-Demand charges per use with no commitment. Reserved Instances and Savings Plans give discounts (up to ~72%) for a 1- or 3-year commitment. Spot offers the deepest discount using spare capacity but can be interrupted with short notice.
4. Which EC2 purchasing option offers the largest discount but can be interrupted by AWS with little notice, suited to fault-tolerant workloads?
- On-Demand Instances
- Spot Instances (correct answer)
- Reserved Instances
- Dedicated Hosts
Spot Instances use spare capacity at steep discounts but can be reclaimed by AWS, making them ideal for interruption-tolerant workloads. Reserved Instances discount long-term steady usage.
5. The AWS Free Tier includes which combination of offer types?
- Only permanently free services
- Only 12-month trials
- Only short-term trials
- Always-free, 12-month free, and short-term trials (correct answer)
The AWS Free Tier has three categories: always free, 12-months free (for new accounts), and short-term free trials.
6. A company runs a steady, predictable EC2 workload 24/7 for three years and wants the lowest cost with a usage commitment. Which pricing option is most cost-effective?
- Reserved Instances or Savings Plans (correct answer)
- On-Demand Instances
- Spot Instances
- Per-second billing without commitment
For steady, long-term usage, Reserved Instances or Savings Plans offer significant discounts in exchange for a 1- or 3-year commitment. On-Demand is more expensive for constant use, and Spot risks interruption.