An organization has a write-intensive mobile application that uses Amazon API Gateway, AWS Lambda, and Amazon DynamoDB. The application has scaled well, however, costs have increased exponentially because of higher than anticipated Lambda costs. The application’s use is unpredictable, but there has been a steady 20% increase in utilization every month.
While monitoring the current Lambda functions, the Solutions Architect notices that the execution-time averages 4.5 minutes. Most of the wait time is the result of a high-latency network call to a 3-TB MySQL database server that is on-premises. A VPN is used to connect to the VPC, so the Lambda functions have been configured with a five-minute timeout.
How can the Solutions Architect reduce the cost of the current architecture?

A.

• Replace the VPN with AWS Direct Connect to reduce the network latency to the on-premises MySQL database.
• Enable local caching in the mobile application to reduce the Lambda function invocation calls.
• Monitor the Lambda function performance; gradually adjust the timeout and memory properties to lower values while maintaining an acceptable execution time.
• Offload the frequently accessed records from DynamoDB to Amazon ElastiCache.
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  B. [*]
• Replace the VPN with AWS Direct Connect to reduce the network latency to the on-premises MySQL database.
• Cache the API Gateway results to Amazon CloudFront.
• Use Amazon EC2 Reserved Instances instead of Lambda.
• Enable Auto Scaling on EC2, and use Spot Instances during peak times.
• Enable DynamoDB Auto Scaling to manage target utilization.
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  C. [*]
• Migrate the MySQL database server into a Multi-AZ Amazon RDS for MySQL.
• Enable caching of the Amazon API Gateway results in Amazon CloudFront to reduce the number of Lambda function invocations.
• Monitor the Lambda function performance; gradually adjust the timeout and memory properties to lower values while maintaining an acceptable execution time.
• Enable DynamoDB Accelerator for frequently accessed records, and enable the DynamoDB Auto Scaling feature.
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  D. [*]
• Migrate the MySQL database server into a Multi-AZ Amazon RDS for MySQL.
• Enable API caching on API Gateway to reduce the number of Lambda function invocations.
• Continue to monitor the AWS Lambda function performance; gradually adjust the timeout and memory properties to lower values while maintaining an acceptable execution time.
• Enable Auto Scaling in DynamoDB.