How AEM TarMK cold standby Setup works

On the primary AEM instance, a TCP port is opened and is listening to incoming messages. Currently, there are two types of messages that the slaves will send to the master:

a message requesting the segment ID of the current head
a message requesting segment data with a specified ID
The standby periodically requests the segment ID of the current head of the primary. If the segment is locally unknown it will be retrieved. If it's already present the segments are compared and referenced segments will be requested too, if necessary.

Note:
Standby instances are not receiving any type of requests, because they are running in sync only mode. The only section available on a standby instance is the Web Console, in order to facilitate bundle and services configuration.

A typical TarMK Cold Standby deployment: