The original topic doesn’t really cover the scenario you’re going to build, so I am not sure where you’re heading. The third scenario on the docs builds a 3 level cluster which typically is what large customer environments have - a master zone, many satellite zones where the checks are scheduled, and agents which only execute local checks.
An agent/client is just an execution bridge for executing local checks. Say, disk, IO, load, etc. - or any type of local access for a RDBMS which cannot be monitored via remote.
The satellite zone specifies where checks are scheduled, they may be executed over at the agents via command endpoint, or fired via remote, some tcp, ping, http checks for instance.
Such a satellite zone can be put into a DMZ within a specified location. Making them two endpoints ensures that the location is still reachable when one of them dies or reloads.
With having multiple satellite zones, you’ll define the hosts and services being checked in each. As said, either directly on the agent or remotely accessible services.
Once you’re built such a scenario with a 3 level cluster, and it works and you know its edge cases and how to troubleshoot it, you can look into more complex setups.
E.g. with adding another layer with two or more satellite zones. master -> satellite-country -> satellite-city -> agent. This is fully supported and also works with the signing methods for setting up agents and satellites, also with config syncs and synchronizing check results.
Still, the more layers are in your cluster tree, the more complex it gets. And typically, granting enough resources to satellite endpoints executing the checks ensures that Icinga scale horizontally.
The key is to try things out before putting it onto production. Or get a training or workshop on this, if it is still unclear.
The Director can be used in any of the described scenarios, you just need to learn how agent hosts and cluster zones work in the background. Still, I’ve found it very convenient - when you know how the Icinga distributed system works of course.