A system with primary and backup nodes (SummitStack) keeps the two systems synchronized by executing the same commands on both.
However, the full data between the EMS servers is not synchronized. The reason for this design decision is to make sure that the control channel is not overloaded when a high number of log messages are generated.
To capture events generated by the primary node onto the backup node, two additional targets are shown in the target commands—one called primary-node and one called backup-node. The first target is active only on the non-primary (backup) EMS server and is used to send matching events to the primary EMS server. The other target is active only on the primary EMS server and is used to send matching events to all other EMS servers.
If the condition for the backup target is met by a message generated on the primary node, the event is sent to the backup node. When the backup node receives the event, it detects if any of the local targets (NVRAM, memory, or console) are matched. If so that event gets processed. The session and Syslog targets are disabled on the backup node, as they are handled on the primary. If the condition for the primary target is met by a message generated on the backup, the event is sent to the primary node.
Note that the backup target is active only on the primary node, and the primary target is active only on the backup node.