AWS SAA-C03 #146
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?
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.
The best solution to meet these requirements would be Option C: Use On-Demand Instances for the baseline level of usage. Use Spot Instances for any additional capacity that the application needs.
Here’s why:
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On-Demand Instances: These instances are suitable for the baseline level of usage because they offer flexible computing power with no upfront costs or long-term commitments. They can be increased or decreased based on the demand of your application, making them ideal for applications with short-term, irregular workloads that cannot be interrupted.
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Spot Instances: Spot Instances allow you to take advantage of unused EC2 capacity in the AWS cloud at a significant discount compared to On-Demand pricing. Spot Instances are recommended for applications that have flexible start and end times, or that are only feasible at very low compute prices. Since your application experiences heavy usage during a specific period each business day and moderate usage overnight, Spot Instances can be used to handle any additional capacity that the application needs during these periods.
This combination allows the company to handle varying levels of application usage efficiently while minimizing EC2 costs. Please note that it’s important to manage Spot Instances properly to avoid interruptions when market conditions change.
Options A, B, and D are not as cost-effective or flexible for this particular use case. For example, Reserved Instances require a long-term commitment and may not provide the flexibility needed for this application’s variable usage patterns. Similarly, Dedicated Instances are typically more expensive and may not offer the cost savings the company is looking for.
Option B suggests using Reserved Instances for the baseline level of usage and Spot instances for any additional capacity that the application needs.
Reserved Instances are a good choice when you have predictable workloads and can commit to using EC2 over a 1-year or 3-year term. They provide a significant discount (up to 75%) compared to On-Demand instance pricing and provide a capacity reservation when used in a specific Availability Zone.
However, in this scenario, the application usage is not entirely predictable. It experiences heavy usage during an 8-hour period each business day, moderate and steady usage overnight, and low usage during weekends. This variable usage pattern may not fully utilize the capacity reserved by Reserved Instances, leading to potential cost inefficiencies.
On the other hand, On-Demand Instances offer flexibility without any upfront cost or long-term commitment, making them more suitable for handling the baseline level of usage in this case. They can be scaled up or down based on demand, which aligns well with the application’s variable usage pattern.
Therefore, while Option B isn’t necessarily incorrect, Option C is more cost-effective and flexible for this particular use case.