Starting with NiagaraAX-3.5, any time a Niagara Runtime Environment (NRE) application boots, it checks the installation “licenses” directory for an flrclient.xml file. This is a file that tells the NRE where to find a “floating license” (the address and port of an FLR server).

The “floating license” uses a hostId value of “FLOATING” instead of a unique hostID.

If the flrclient.xml file is present and valid, the NRE tries to get a license from one of the FLRs defined in the file. If the file is present but not valid, or if the file is not present at all, the NRE attempts to load a local (node-locked) license. The NRE instance does not start unless it is licensed.After the NRE application instance successfully starts using a floating license, the license manager continues to send periodic heartbeat messages to the FLR to maintain its lease on the floating license. As long as this heartbeat mechanism is working, the application continues to run. If heartbeats start failing, a retry-loop is entered and the application eventually is forced to stop unless it starts getting heartbeats again.When the application stops, the license manager indicates to the FLR that it no longer needs the license so that another application can start using that license, if needed. In the case of an ungraceful stop, the FLR eventually auto-releases the license after a set period of failed heartbeats.

Also see Example FLR scenarios.