Explanation

Correct Answer: D

Why Option D is correct:

1. Cost Optimization: AWS Lambda is serverless and only runs when invoked, so there's no cost for idle compute resources. This minimizes costs compared to running a dedicated EC2 instance (Option C) or using third-party solutions (Option B).
2. Minimal Infrastructure Maintenance: Lambda functions require no server management, patching, or maintenance. Amazon EventBridge (formerly CloudWatch Events) provides a fully managed event bus service.
3. Automated Scheduling: EventBridge can be configured with cron expressions to invoke the Lambda function on a schedule (e.g., start instances at 8 AM, stop instances at 6 PM).
4. Native AWS Integration: The Lambda function can use AWS SDKs to call EC2 and RDS APIs to start/stop instances, providing a fully managed AWS-native solution.

Why other options are incorrect:

Option A:

• Elastic resize is for Redshift clusters, not EC2 instances
• RDS instances cannot be scaled to zero; you can only stop them, which is different from scaling to zero
• This approach doesn't provide automated scheduling

Option B:

• While AWS Marketplace solutions might work, they typically incur additional costs
• Third-party solutions require additional management and may not be as tightly integrated
• Doesn't minimize infrastructure maintenance as much as a serverless solution

Option C:

• Requires launching and maintaining another EC2 instance, which adds cost
• Requires managing the instance (patching, security, monitoring)
• The crontab solution adds operational overhead
• Doesn't minimize infrastructure maintenance

Key AWS Services Used:

• AWS Lambda: Serverless compute service
• Amazon EventBridge: Serverless event bus for scheduling
• Amazon EC2: For compute instances
• Amazon RDS: For database instances

Best Practice: This solution follows AWS best practices for cost optimization by using serverless services to manage infrastructure lifecycle, eliminating the need for dedicated management servers.