AWS Certified Solutions Architect - Associate
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A company runs a stateless web application in production on a group of Amazon EC2 On-Demand Instances behind an Application Load Balancer. The application experiences heavy usage during an 8-hour period each business day. Application usage is moderate and steady overnight. Application usage is low during weekends.
The company wants to minimize its EC2 costs without affecting the availability of the application.
Which solution will meet these requirements?
Other
Community
UAnonymous
A
Use Spot Instances for the entire workload.
B
Use Reserved Instances for the baseline level of usage. Use Spot Instances for any additional capacity that the application needs.
C
Use On-Demand Instances for the baseline level of usage. Use Spot Instances for any additional capacity that the application needs.
D
Use Dedicated Instances for the baseline level of usage. Use On-Demand Instances for any additional capacity that the application needs.
Explanation:
Explanation
Correct Answer: B
Why Option B is correct:
- Reserved Instances for baseline usage: The application has a predictable baseline load (moderate overnight usage and low weekend usage). Reserved Instances provide the lowest cost for predictable, steady-state workloads with a commitment of 1-3 years.
- Spot Instances for additional capacity: During the 8-hour peak period each business day, the application needs additional capacity. Spot Instances offer up to 90% discount compared to On-Demand Instances and are suitable for stateless, fault-tolerant workloads that can handle interruptions.
- Cost optimization: This combination minimizes costs while maintaining availability:
- Reserved Instances ensure baseline capacity at the lowest cost
- Spot Instances provide additional capacity during peaks at significant savings
- The stateless nature of the application makes it suitable for Spot Instances
Why other options are incorrect:
A. Use Spot Instances for the entire workload:
- Spot Instances can be interrupted with 2-minute notice
- Using them for the entire workload would affect availability, especially for baseline overnight and weekend usage
- Not suitable for production workloads that require guaranteed availability
C. Use On-Demand Instances for baseline, Spot for additional:
- On-Demand Instances are more expensive than Reserved Instances for baseline usage
- This doesn't minimize costs as effectively as using Reserved Instances for baseline
D. Use Dedicated Instances for baseline, On-Demand for additional:
- Dedicated Instances are the most expensive option and provide physical isolation
- This is not cost-optimized and is typically used for compliance/regulatory requirements
- On-Demand for additional capacity is more expensive than using Spot Instances
Key AWS Concepts:
- Reserved Instances: Best for predictable workloads with steady-state usage
- Spot Instances: Best for fault-tolerant, flexible workloads that can handle interruptions
- On-Demand Instances: Pay-as-you-go with no commitment, most flexible but most expensive
- Dedicated Instances: Physical isolation for compliance, most expensive option
Best Practice: For production workloads with predictable baseline and variable peaks, use Reserved Instances for baseline and Spot Instances for peaks to achieve optimal cost savings while maintaining availability.
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