What an Admin Node is

You perform most day-to-day activities using the Grid Management Interface, which resides on Admin Nodes. Admin Nodes provide services for the web interface, system configuration, and audit logs. Each site in a StorageGRID Webscale deployment can have one or more Admin Nodes.

Admin Nodes use the AMS service, the CMN service, and the NMS service.
Admin Node overview

What the AMS service is

The Audit Management System (AMS) service tracks system activity and events.

What the CMN service is

The Configuration Management Node (CMN) service manages system-wide configurations of connectivity and protocol features needed by all services. In addition, the CMN service is used to run and monitor grid tasks. There is only one CMN service per StorageGRID Webscale deployment. The Admin Node that hosts the CMN service is known as the primary Admin Node.

What the NMS service is

The Network Management System (NMS) service powers the monitoring, reporting, and configuration options that are displayed through the Grid Management Interface, the StorageGRID Webscale system's browser-based interface.