Failover License Servers – why can’t I have 3?

The question often comes up - "I am used to failover servers configured in a triad (3).  Why can't RLM support this?"

Whenever this happens, it is because someone is used to the way that FLEXlm configures redundant servers.

The reality is this - RLM and FLEXlm work differently with respect to server failover,  and the RLM method is easier for the end-user to configure, while providing the same amount of server redundancy.  In a FLEXlm redundant-server configuration, a little-known fact is this:

the third server can never serve licenses

This is because, in FLEXlm, 2 of the 3 servers must be running to have the system operate.  So, either servers 1 and 2, 2 and 3, or 1 and 3 must be running.  And FLEXlm (at least until version 10.?) always picks the server whose name is first in an alphabetical sort (we know, we wrote the code).   So the server with the last name, alphabetically, will never serve licenses.

By contrast, with RLM, you pick a primary license server, and a failover server.  If the primary goes down, the failover takes over. There is no 3rd server to configure.  There is no situation where 3 FLEXlm servers would serve licenses that RLM will not serve licenses (assuming RLM is configured on 2 of the 3 FLEXlm servers).  In other words:

adding a 3rd RLM server buys you nothing, other than extra administrative overhead