Looks as if you have not setup your ha setup correctly, as the mirror function that is builtin to ispconfig takes care about creating the website users on all slave servers in the ha setup. You should take a look into the multiserver / mirror setup guide.
When using multiple Setup with glusterfs, i saw that someone complain it with 2 different Mysql databases for each node. If alle Users use the same Database, setup and configuration is much easier and if the Master goes down, every Client can configure his Application ahead.
Every node needs its own mysql db to create a ha setup. Your setup with just one mysql install would introduce a single point of failure.