AWS Certified Solutions Architect – Professional — Question 1015

A media storage application uploads user photos to Amazon S3 for processing. End users are reporting that some uploaded photos are not being processed properly. The Application Developers trace the logs and find that AWS Lambda is experiencing execution issues when thousands of users are on the system simultaneously. Issues are caused by:
✑ Limits around concurrent executions.
✑ The performance of Amazon DynamoDB when saving data.
Which actions can be taken to increase the performance and reliability of the application? (Choose two.)

Answer options

• A. Evaluate and adjust the read capacity units (RCUs) for the DynamoDB tables.
• B. Evaluate and adjust the write capacity units (WCUs) for the DynamoDB tables.
• C. Add an Amazon ElastiCache layer to increase the performance of Lambda functions.
• D. Configure a dead letter queue that will reprocess failed or timed-out Lambda functions.
• E. Use S3 Transfer Acceleration to provide lower-latency access to end users.

Correct answer: B, D

Explanation

Adjusting the Write Capacity Units (WCUs) resolves the DynamoDB bottleneck since the performance issue occurs when saving (writing) data. Setting up a dead letter queue (DLQ) ensures that any Lambda executions that fail due to concurrency limits or timeouts are captured and can be reprocessed, which directly increases application reliability. Other options like adjusting RCUs, adding ElastiCache, or using S3 Transfer Acceleration do not address the specific write bottlenecks or Lambda concurrency failures mentioned in the scenario.