Cost-Effective S3 Thumbnail Generation with Lambda

SAA-C03 By islever Editorial Last updated

Design cost-optimized compute solutions.

Short answer

C Configure an S3 event notification to invoke an AWS Lambda function each time a user uploads a new photo to the application.

Question

A company runs an application that stores and shares photos. Users upload the photos to an Amazon S3 bucket. Every day, users upload approximately 150 photos. The company wants to design a solution that creates a thumbnail of each new photo and stores the thumbnail in a second S3 bucket. Which solution will meet these requirements MOST cost-effectively?
  1. Configure an Amazon EventBridge scheduled rule to invoke a script every minute on a long-running Amazon EMR cluster. Configure the script to generate thumbnails for the photos that do not have thumbnails. Configure the script to upload the thumbnails to the second S3 bucket.
  2. Configure an Amazon EventBridge scheduled rule to invoke a script every minute on a memory-optimized Amazon EC2 instance that is always on. Configure the script to generate thumbnails for the photos that do not have thumbnails. Configure the script to upload the thumbnails to the second S3 bucket.
  3. Configure an S3 event notification to invoke an AWS Lambda function each time a user uploads a new photo to the application. Configure the Lambda function to generate a thumbnail and to upload the thumbnail to the second S3 bucket. Correct Answer
  4. Configure S3 Storage Lens to invoke an AWS Lambda function each time a user uploads a new photo to the application. Configure the Lambda function to generate a thumbnail and to upload the thumbnail to a second S3 bucket.

Key Takeaways

Tests the ability to choose serverless, pay-per-use services (Lambda) over always-on infrastructure (EC2/EMR) for infrequent tasks to minimize costs.

Determines the most cost-effective method for generating thumbnails from new S3 uploads using event-driven architecture. The solution leverages S3 Event Notifications to trigger AWS Lambda, eliminating idle compute costs.

Common mistake: Candidates often select EC2 or EMR options because they are familiar with batch processing, failing to recognize that 'always on' instances incur continuous charges even when idle.

Expert Analysis

Why the Answer Is Correct

Option C is the correct answer because it uses an event-driven architecture that aligns perfectly with the requirement for cost-effectiveness. S3 Event Notifications automatically trigger an AWS Lambda function only when a new object is uploaded. Since the volume is low (150 photos/day), you only pay for the compute time used during execution. There are no idle resources, making this the cheapest approach.

Why the Other Options Are Wrong

Options A and B involve scheduled rules invoking scripts on long-running clusters or instances. Keeping an Amazon EMR cluster or an EC2 instance running 'always on' incurs significant hourly costs regardless of whether work is being processed. Option D is incorrect because S3 Storage Lens is a usage monitoring and trend analysis tool; it does not have the capability to invoke Lambda functions or process objects.

Community Comment Notes

The community consensus strongly supports Option C. Users like swati1508 and komorebi explicitly confirm that C is the correct choice, highlighting the standard exam pattern for this scenario. One user noted the simplicity of the solution, reinforcing that event-driven Lambda is the expected best practice for this specific workload.

Exam Strategy

When asked for the 'most cost-effective' solution involving S3 triggers, immediately look for Lambda combined with S3 Event Notifications. Avoid any option that suggests keeping servers (EC2/EMR) running continuously unless the workload is massive and constant.

Frequently Asked Questions

Why is EC2 not cost-effective here?

EC2 incurs hourly charges while running. For 150 daily uploads, paying for 24/7 uptime is far more expensive than paying milliseconds of Lambda time.

Can S3 Storage Lens trigger Lambda?

No. S3 Storage Lens is strictly for analytics and dashboards. It cannot execute code or interact with other AWS services like Lambda.

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Community Votes

C
100%

100% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 4 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 4

  1. [Removed] 👍 3 Answered C
    C. Configure an S3 event notification to invoke an AWS Lambda function each time a user uploads a new photo to the application. Configure the Lambda function to generate a thumbnail and to upload the thumbnail to the second S3 bucket.
  2. ieffiong 👍 1 Answered C
    Take a sip of water and smile, you're almost there.
  3. swati1508 👍 2
    C is correct
  4. komorebi 👍 2 Answered C
    Answer is C

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