Exam AWS Certified Solutions Architect - Associate SAA-C03 topic 1 question 167 discussion

"without any downtime" - Reserved Instances for the baseline capacity "MOST cost-effectively" - Spot Instances to handle additional capacity

D is the correct answer

baseline capacity" refers to the normal or expected capacity performance of a system or process, so use reserved instance - this to fulfil without any downtime and cost-effective if "additional capacity" refers to resources or capabilities beyond the standard or baseline capacity needed to handle normal operations, allowing for flexibility and the ability to handle surges in demand or unexpected events - then we should use on-demand instances

C is correct because it balances cost and reliability using a combination of: - Reserved Instances for steady-state traffic (ensuring continuous processing). - Spot Instances for handling spikes in traffic (reducing costs significantly). A - ❌ Not Reliable – Spot Instances can be interrupted at any time. Using them exclusively could cause processing delays or failures. B - ❌ Not Cost-Effective – RIs are best for predictable workloads, but over-provisioning for peak loads leads to unnecessary costs when traffic is low. D - ❌ More Expensive Than Spot Instances – On-Demand Instances are more costly than Spot Instances for handling additional capacity.

I believe the best fit for the scenario is D. D has a portion that is about 90% more expensive than C. However, Spot instances can be interrupted which means that some of the processes can be interrupted, which is not acceptable. So considering that I am choosing D.

Easily the most cost effective

Spot Instances – Can be scaled up dynamically when message volume increases, at a much lower cost than On-Demand instances.

Why Option C is Correct: Reserved Instances: Provide a cost-effective solution for the baseline capacity (predictable, steady traffic) with a significant discount compared to On-Demand Instances. Spot Instances: Are highly cost-effective (up to 90% cheaper than On-Demand Instances) and can be used for handling additional, variable traffic since the application processes messages in parallel and can tolerate instance interruptions. Combining these instance types ensures a balance of cost savings and availability.

I think it is C The instance will remove the message from the queue when it is already processed, there is one downside here when the spot instance is terminated before message removal, it will lead to double processing. The question is not talking about time, so having baseline + spot is the most cost effective here.

C - Because of cost effectiveness.

D. Use Reserved Instances for the baseline capacity and use On-Demand Instances to handle additional capacity. Most Voted

"without any downtime" rules out spot instance.

Comparison with other options: A. Spot Instances exclusively: While cost-effective, Spot Instances can be interrupted and may not ensure uninterrupted message processing, which is critical for this application. B. Reserved Instances exclusively: Over-provisioning Reserved Instances to handle the maximum capacity would lead to unnecessary costs during low-traffic periods. D. Reserved Instances + On-Demand Instances: On-Demand Instances are more expensive than Spot Instances for handling additional capacity, making this less cost-effective.

Ans D - "Continual processing" rules out Spot; so its Reserved Instances for the baseline capacity and use On-Demand Instances for peak

without any downtime - Reserved Instances for the baseline capacity cost-effectively - Spot Instances to handle additional capacity

C. Use Reserved Instances for the baseline capacity and use Spot Instances to handle additional capacity.

First we need to ensure that no downtime. Then we can talk about cost-effective.