The ability to add web servers dynamically during peak user activity and remove them when user activity decreases is an example of:

Configuration automation focuses on applying software and system settings to existing infrastructure components, not on the dynamic creation or destruction of the infrastructure itself.

Build automation primarily concerns the compilation, testing, and packaging of software source code into deployable artifacts, which is distinct from managing server lifecycles.

Infrastructure automation involves programmatically provisioning, configuring, and managing computing infrastructure like servers, networks, and storage. Dynamically adding and removing web servers based on user activity directly aligns with the goal of managing infrastructure automatically to meet fluctuating demands.

Inventory management is the process of tracking and cataloging existing IT assets, but it does not encompass the automated provisioning and de-provisioning of those assets.