AWS Certified Solutions Architect - Associate
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A company hosts a web application on multiple Amazon EC2 instances. The EC2 instances are in an Auto Scaling group that scales in response to user demand. The company wants to optimize cost savings without making a long-term commitment.
Which EC2 instance purchasing option should a solutions architect recommend to meet these requirements?
Other
Community
UAnonymous
A
Dedicated Instances only
B
On-Demand Instances only
C
A mix of On-Demand Instances and Spot Instances
D
A mix of On-Demand Instances and Reserved Instances
Explanation:
Explanation
Correct Answer: C - A mix of On-Demand Instances and Spot Instances
Why this is correct:
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Cost optimization without long-term commitment: Spot Instances provide significant cost savings (up to 90% off On-Demand prices) without requiring any long-term commitment, unlike Reserved Instances which require 1- or 3-year commitments.
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Auto Scaling compatibility: Spot Instances work well with Auto Scaling groups. When using a mixed instances policy, Auto Scaling can launch Spot Instances when capacity is available and fall back to On-Demand Instances when Spot capacity is unavailable.
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Fault-tolerant workload suitability: Web applications that can handle interruptions (like those behind a load balancer) are ideal candidates for Spot Instances. If a Spot Instance is interrupted, Auto Scaling can automatically replace it with another instance.
Why other options are incorrect:
A. Dedicated Instances only:
- Most expensive option
- Provides physical isolation but no cost savings
- Doesn't address the requirement for cost optimization
B. On-Demand Instances only:
- No cost savings compared to Spot Instances
- Pay full price without any discounts
- Doesn't optimize costs as requested
D. A mix of On-Demand Instances and Reserved Instances:
- Requires long-term commitment (1 or 3 years)
- Violates the requirement of "without making a long-term commitment"
- While it provides cost savings, it doesn't meet the no-commitment requirement
Best Practice Implementation:
For this scenario, the solutions architect should recommend:
- Mixed instances policy in the Auto Scaling group
- Configure capacity rebalancing to proactively replace Spot Instances that are at risk of interruption
- Use Spot Fleet or EC2 Auto Scaling with Spot integration
- Set appropriate instance diversification to use multiple instance types and Availability Zones
- Configure interruption handling to gracefully handle Spot interruptions
This approach maximizes cost savings while maintaining application availability and avoiding long-term commitments.
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