AWS Certified Solutions Architect - Associate
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A company is running a custom application on Amazon EC2 On-Demand Instances. The application has frontend nodes that need to run 24 hours a day, 7 days a week and backend nodes that need to run only for a short time based on workload. The number of backend nodes varies during the day.
The company needs to scale out and scale in more instances based on workload.
Which solution will meet these requirements MOST cost-effectively?
Other
Community
UAnonymous
A
Use Reserved Instances for the frontend nodes. Use AWS Fargate for the backend nodes.
B
Use Reserved Instances for the frontend nodes. Use Spot Instances for the backend nodes.
C
Use Spot Instances for the frontend nodes. Use Reserved Instances for the backend nodes.
D
Use Spot Instances for the frontend nodes. Use AWS Fargate for the backend nodes.
Explanation:
Explanation
Correct Answer: B
Why Option B is correct:
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Frontend nodes (24/7 workload): Reserved Instances provide the most cost-effective solution for steady-state, predictable workloads that run continuously. By committing to a 1-year or 3-year term, companies can save up to 72% compared to On-Demand pricing.
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Backend nodes (variable, short-term workload): Spot Instances are ideal for flexible, interruptible workloads that can handle potential interruptions. They offer up to 90% savings compared to On-Demand pricing. Since backend nodes only run for short periods based on workload and can scale in/out, Spot Instances provide the best cost optimization.
Why other options are incorrect:
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Option A: AWS Fargate is a serverless compute engine for containers, but it's generally more expensive than Spot Instances for variable workloads. Fargate is better suited for containerized applications where you don't want to manage infrastructure, but for pure cost optimization of EC2 workloads, Spot Instances are superior.
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Option C: This option reverses the optimal strategy. Spot Instances are not suitable for 24/7 frontend nodes because they can be interrupted, which would cause service disruption. Reserved Instances are not suitable for variable backend nodes because you pay for them even when they're not running.
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Option D: Again, Spot Instances are not suitable for 24/7 frontend nodes due to potential interruptions. While Fargate could work for backend nodes, it's not the most cost-effective option compared to Spot Instances.
Key AWS Concepts:
- Reserved Instances: Best for predictable, steady-state workloads
- Spot Instances: Best for flexible, fault-tolerant, interruptible workloads
- On-Demand Instances: Pay-as-you-go with no commitment
- Fargate: Serverless compute for containers (pay for vCPU and memory resources consumed)
This solution provides the optimal balance of reliability for the frontend (Reserved Instances) and maximum cost savings for the variable backend workload (Spot Instances).
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