What feature of AWS Lambda allows it to be truly serverless?

The characteristic of AWS Lambda that allows it to be truly serverless is automatic scaling based on demand. This feature means that AWS Lambda can automatically handle the number of requests and execute functions in response to these requests without requiring manual intervention or the need to provision or manage servers. As usage increases or decreases, Lambda can adapt by automatically scaling the resources needed to handle incoming requests, ensuring that performance remains efficient and cost-effective.

This serverless architecture abstracts the underlying server infrastructure away from the user. Users do not need to worry about capacity planning, scaling, or maintenance of the servers, allowing them to focus on writing code and building applications. The operational burden of managing the infrastructure is offloaded to AWS, enabling developers to build and deploy applications more rapidly and efficiently.

Other options, while they may have relevance in different contexts, do not capture the essence of what makes Lambda serverless. For instance, integration with EC2 instances does not inherently confer serverless capabilities, as EC2 involves managing instances. Pre-provisioned resources and static resource allocation also suggest a level of management and operational overhead that is contrary to the core serverless principle of automatically managing scaling and capacity based on demand.