The Prisma SD-WAN architecture is built on a centralized management model where the controller maintains a persistent and secure connection with all managed ION devices. When an administrator creates or modifies a configuration element, such as a custom application definition, the change is saved on the controller. The controller then automatically and immediately pushes the updated configuration to all ION devices in the network. This ensures configuration consistency across the SD-WAN fabric without requiring manual intervention, device reboots, or waiting for a scheduled update cycle.

A. No manual "Push" action is required for this type of configuration change; the controller propagates it automatically upon saving.

B. Rebooting an ION device is a service-impacting action and is not required for applying configuration updates like application definitions.

D. Custom application definitions are user-defined configuration objects, distinct from the global Palo Alto Networks App-ID signature database, which is updated on a schedule.

1. Palo Alto Networks Prisma SD-WAN Administrator's Guide: In the section on Application Definitions, the process of creating and managing custom applications is described. The guide states, "When you define a custom application, the controller automatically distributes this definition to all ION devices." This confirms the automatic and immediate propagation of the change. (Reference: Prisma SD-WAN Administrator's Guide, section "Define a Custom Application").

2. Palo Alto Networks Prisma SD-WAN Design and Sizing Guide: This guide describes the architecture, noting that the controller is the single source of truth for policy and configuration. It explains that "Configuration and policy changes are made centrally on the controller and are automatically propagated to the ION devices," which supports the immediate and automated nature of the update process. (Reference: Prisma SD-WAN Design and Sizing Guide, section "Prisma SD-WAN Controller Architecture").