What it is
The UMS is the server the endpoints answer to. Configuration, grouping, monitoring, policies, firmware, certificates, network settings and software packages all come from it, applied to a single device or to a group. It manages IGEL OS 11 and 12 side by side, which matters because most estates are mid-migration for longer than they planned.
Two consoles, on purpose
UMS 12 has a browser-based Web App and a Java-based Console. The Web App is where day-to-day work happens; the Console still carries the deeper administrative functions. Anyone expecting the browser to have replaced the desktop client will be disappointed for a while yet, and it is better to know that before the rollout plan says otherwise.
How it talks to the endpoints
Through the Unified Protocol, a WebSocket connection that carries everything between UMS 12 and IGEL OS 12, and only between those two. One consequence is worth the sentence: because it is a single WebSocket, an external load balancer such as F5 BIG-IP or Citrix NetScaler can sit in front of it, which is how you get load distribution and availability in the management layer rather than in a script.
For real high availability there is Distributed UMS: several UMS servers on one shared database.
What the licence level decides
All IGEL OS Editions include a UMS licence, so the question is never whether you have one. It is which one. An external database, the IGEL Cloud Gateway and Distributed UMS arrive with Standard; the distributed app repository and using the UMS as a certificate authority proxy arrive with Enterprise.
Downgrading takes features away immediately, and IGEL says so in the manual. Nothing is deleted, so an upgrade restores it, but the afternoon in between is real.