Which AWS service pattern is best for running code in response to events with automatic scaling and pay-per-use pricing?

• A. AWS Lambda
• B. Amazon EC2
• C. AWS Fargate
• D. AWS Lightsail

Answer: (A)

Event-driven, on-demand compute that scales automatically and charges only for actual usage. AWS Lambda is designed for code that runs in response to events, such as a file upload to storage, a message in a queue, or an API call. It automatically scales out to handle bursts of events, and you’re billed only for the compute time and invocations, with no need to provision or manage servers.

This fits the pattern perfectly because the core advantage is responding to events with automatic scaling and pay-per-use pricing. In contrast, traditional virtual machines like EC2 require you to provision capacity and configure scaling groups, meaning you pay for running instances even when idle. Container-based options like Fargate do offer on-demand scaling, but they introduce container orchestration and management overhead for event-driven tasks. Lightsail is simpler but not designed for automatic, event-driven scaling at the granularity Lambda provides.