You would like to know what is and how is configured the Subscriber URL when configuring a cluster, because you found in the Aurea Monitor Management Server Guide, in the section Clustering -> Introduction saying that you have to "make sure that the Subscriber URL for all members of the cluster is configured with the URL of the load balancer."
Unfortunately, this is outdated information and a mistake in the documentation.
To have Monitor Agents connect to the correct Aurea Monitor Management Server (AMS) you will have to configure the URL parameter of the AMS (or the URL of the load balancer) in the configuration.json of the Agent (found in the root folder). This is since AMS version v11.x.
Your configuration.json should look something like this:
# Template for configuring an HTTP proxy (uncomment the following lines):
# host: "localhost",
# port: 8080
Our documentation team has been notified to fix this outdated information.
Agent-only: The Documentation Task to have this updated is ACTA-61875