The best way to automate the scale-out of the application layer using a third-party tool is to create a Playbook with a webhook as a trigger and a REST API call as an action. A webhook is a mechanism that allows a third-party service to send a notification to a Calm server when a certain event occurs, such as a code commit or a build completion. A REST API call is a way to interact with the Calm server programmatically, such as launching a blueprint or scaling out a service. By creating a Playbook that combines these two elements, the administrator can enable the third-party tool to trigger the scale-out action on the Calm server with a single command. The other options are either not feasible, not efficient, or not relevant for this task. References: Nutanix Calm: Playbooks - Read the Docs and Nutanix Calm: REST API - Read the Docs.