Which actions can be taken to increase the performance and reliability of the application?

Explanations:

Read capacity units (RCUs) determine the read throughput of a DynamoDB table. Since the problem is with Lambda execution during high concurrency, not with reading data from DynamoDB, adjusting RCUs will not solve the core issue. The problem lies with saving data (write operations) and Lambda concurrency limits.

Write capacity units (WCUs) determine the write throughput of a DynamoDB table. If Lambda functions are experiencing performance issues when saving data to DynamoDB, it indicates that the table’s WCUs might be insufficient for the high volume of writes during peak usage. Adjusting WCUs will improve write performance and prevent throttling, thus improving the reliability of Lambda functions.

ElastiCache is a caching service for frequently accessed data. It does not directly improve the performance of Lambda functions themselves or address concurrency limits. The issue is with Lambda execution and DynamoDB write performance, not with caching data for Lambda.

Configuring a dead-letter queue (DLQ) is an essential practice for handling failed or timed-out Lambda invocations. When a Lambda function fails, the invocation record is sent to the DLQ. This allows for asynchronous reprocessing of failed invocations, improving the reliability of the application by ensuring that failed processing attempts are retried. This addresses the issues caused by concurrency limits and potential Lambda errors.

S3 Transfer Acceleration is a feature that accelerates uploads and downloads to S3 by using CloudFront edge locations. This improves the performance of transferring filesto and fromS3, but it does not address the Lambda execution issues or DynamoDB performance problems. The problem is not with uploading photos to S3, but with processing themafterthey have been uploaded.