Hey, sorry about the delay in response!

There's no difference between the JDBC realms other than their names. The failover is to an exact replica on a different server, yes. In fact it's using bi-directional replication between the two databases to ensure the content is the same.

The DB is PostgreSQL.

That's a great question, the answer at this point is, "my solution is still in progress". See my latest question posed as it's entirely related to what you asked: Client config for HA EJB RMI

From my theoretical current perspective though, my plan was to hold configurations to each host controller within the client application. On specific exceptions related to connection failure, try another destination (failover) with the failed invocation. The clustering and DB bi-directional replication would provide the underlying support for displaced invocations (i.e. host controller X is unresponsive, so host controller Y was used (data and state is the same thanks to DB replication and Infinispan)).

This problem with the authentication piece, however, means that if the primary realm is down, I have to change the Wildfly profile (a manual action assuming I didn't deploy some hacky script to cron) to prefer the secondary realm to get authentication back up. This isn't the end of the world or anything, but it was a capability of the WildFly 10 security system.

The DB driver approach is an interesting perspective, I hadn't considered that as a workaround. I'll look into that, thanks!