An API team runs an AWS Lambda function behind an Application Load Balancer (ALB). During predictable hourly traffic spikes, p95 response latency increases due to occasional cold starts. The team wants stable latency during those spikes without permanently overprovisioning resources for all functions. Which configuration is the most appropriate way to reduce cold starts for this Lambda function?

Increase the function memory size and rely on faster initialization to reduce cold starts.

More memory can improve CPU performance and may reduce initialization time in some cases, but it does not guarantee that execution environments are already warm when traffic spikes. Cold starts can still occur.

Set reserved concurrency equal to the expected peak requests per second for the function.

Reserved concurrency primarily limits or guarantees concurrency. It helps control throttling and allocation, but it does not pre-warm environments. Therefore it does not directly prevent cold-start latency spikes.

Use an event source mapping with a higher batch size so Lambda triggers earlier and keeps the runtime warm.

Event source mappings apply to event sources such as SQS, Kinesis, or DynamoDB streams. For an ALB-triggered Lambda (synchronous request/response), batch size is not a mechanism to guarantee warm environments or to mitigate cold starts.

What does this SAA-C03 question test?

Read the scenario before looking for a memorised answer.

What is the correct answer to this question?

The correct answer is: Publish a version of the function and configure provisioned concurrency on an alias, using autoscaling for the alias. — Use provisioned concurrency on a published version attached to an alias. Provisioned concurrency keeps a specified number of execution environments initialized and ready to handle ALB-invoked requests, which directly reduces cold-start latency. Using the alias model allows the team to manage and autoscale warm capacity for those predictable hourly spikes rather than relying on default on-demand initialization behavior. Why others are wrong: Increasing memory or adjusting reserved concurrency can change performance and limits, but they do not ensure pre-initialized execution environments are available during bursts. Event source mapping configuration is not applicable for ALB-triggered synchronous invocation in a way that would reliably prevent cold starts.

What should I do if I get this SAA-C03 question wrong?

Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.