SAA-C03 Q295 · Cost

Question

A company runs a custom application on Amazon EC2 On-Demand Instances. The application has frontend nodes that must run 24/7. The backend nodes only need to run for short periods depending on the workload. Frontend nodes accept jobs and place them in queues. Backend nodes asynchronously process jobs from the queues, and jobs can be restarted. The company wants to scale infrastructure based on workload, using the most cost-effective option. Which solution meets these requirements MOST cost-effect

Accepted Answer

**Answer B: Reserved Instances (frontend) + Spot Instances (backend)**

Let's map each requirement to the solution:

1. **Frontend nodes run 24/7** → **Reserved Instances** are the most cost-effective option for steady-state, always-on workloads. They provide up to **72% discount** compared to On-Demand pricing in exchange for a 1-year or 3-year commitment. Since frontends must always be running, this commitment is justified.

2. **Backend nodes run for short periods** → **Spot Instances** offer up to **90% discount** compared to On-Demand. They are ideal for short-lived, variable workloads.

3. **Jobs can be restarted** → This is the critical clue that makes Spot Instances viable for the backend. Spot Instances can be interrupted by AWS with a 2-minute warning. Since the jobs are pulled f

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