The database can be sharded, and placed across many machines, but that is by the by. The compute system could be clustered using BeeOND, again an interesting option, if the master was running BeeGFS, neither are simple, or straightforward.
The environment is complex as its demands are high availability, higher transaction throughput, and high network capability, with the ease/ability to back up and restore. All of this on a custom software platform - it's not as simple as it seems, and Susan has done a brilliant job at making it do all of this on a (very) limited budget.
Sno