I think I've seen during one training that it is possible to receive alarms on a DMS coming from another DMS, but I can't remember how it was possible. Can I use the internal NATS messaging of a DMS to share information with another DMS ?
No from DMS to DMS. We have many DMAs on 1 DMS, and other DMAs on another DMS
A way of doing it could be by using an SNMP Manager on the DMS that needs to forward the alarms and a trap receiver on the receiving DMS. The SNMP Manager can have an alarm filter to only forward the needed alarms, and can potentially resend the active alarms every X minutes.
An other way could be by polling the alarms out of the first system by the standard web API by a driver on the second DMS. The Skyline DataMiner System driver can do this for example.
Do you mean from one DMA to another DMA ? DMS is a collection of DMAs (cluster of DMAs)