SAA-C03 Design Cost-Optimized Architectures Practice Question
A video processing pipeline runs batch jobs that are safe to interrupt and restart. The jobs checkpoint progress to durable storage every few minutes, and the team can automatically resubmit from the last checkpoint. They want to minimize compute cost while accepting that capacity can be interrupted. Which launch configuration for the processing workers is the best cost-optimized choice?
⚠ Common exam trap
Many exam-takers choose On-Demand or Reserved Instances because they assume interruptions are unacceptable, but the question explicitly states the workload is safe to interrupt and restart, making Spot Instances the correct cost-optimized choice.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Launch the worker nodes as Spot Instances, and configure the job resubmission logic to restart from checkpoints upon interruption.
Spot Instances offer significant cost savings (up to 90% compared to On-Demand) and are ideal for fault-tolerant, interruptible workloads. Since the pipeline checkpoints progress to durable storage and can automatically resume from the last checkpoint, using Spot Instances minimizes compute cost while accepting interruptions.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Launch the worker nodes as Spot Instances, and configure the job resubmission logic to restart from checkpoints upon interruption.
Why this is correct
Spot provides significantly lower pricing than On-Demand for EC2 capacity. Because the workload is designed to tolerate interruption (checkpointing + resubmission from the last checkpoint), the team can safely accept Spot interruptions. Resubmission from durable checkpoints preserves correctness while still capturing the cost advantage of Spot.
- ✗
Launch the worker nodes as On-Demand Instances with no interruption handling so the pipeline never needs resubmission.
Why it's wrong here
On-Demand Instances are priced at the full hourly rate with no Spot discount, directly contradicting the scenario's requirement to minimize compute cost. While On-Demand instances are not reclaimed by AWS due to Spot capacity needs, they can still fail from hardware issues or AZ disruptions, so claiming the pipeline 'never needs resubmission' is false. Moreover, the pipeline already implements checkpointing and resubmission logic specifically to tolerate interruption; paying a premium to avoid interruptions that are cost-neutral to the design is a wasteful trade-off.
- ✗
Launch the worker nodes as Reserved Instances to guarantee capacity and reduce cost, ignoring interruptions.
Why it's wrong here
Reserved Instances discount On-Demand pricing but do not align with the scenario’s goal of accepting interruption for maximum savings. Also, ignoring interruptions conflicts with the operational reality that interruptions can still occur (and the scenario specifically provides checkpointing logic to handle interruption safely). The best approach is therefore to use Spot with interruption-aware resubmission.
- ✗
Use Savings Plans and also set the job scheduler to never start new jobs unless previous jobs finish without interruption.
Why it's wrong here
Savings Plans are commitment-based and can reduce cost, but the added scheduler constraint removes the ability to efficiently recover from interruption and undermines the pipeline’s interrupt-tolerant design. The scenario’s key cost lever is accepting interruptions using Spot, not avoiding them with restrictive scheduling.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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