A Server triad can be used to provide redundancy for the license server. In a triad configuration, the license server runs across three machines.
As long as at least two of the three machines are operational, licenses can continue to be issued.
If three machines are not available for a Server triad, a dongle-based license may be a suitable alternative.
With a dongle-based license, the license is tied to a USB dongle rather than to a specific machine. As long as the dongle is connected, the license server can run.
This also allows the license to be moved to another machine if the primary license server becomes unavailable. Simply connect the dongle to the replacement machine and start the license server.
Dongle drivers will be required on any machine where the dongle will be connected.