Earlier quoted context omitted.
> Tricky networking though. And data storage/locality/consistency.
Databases are rarely the bottleneck during access volume spikes in my experience. It’s really impressive how far some beefy servers and a read copy can take you. But if that is your bottleneck you should be upgrading your DB system regardless of whether you’re on cloud or bare metal.
Yes, you can solve the problem with sharding and other tricks, but for many banks, the mainframe is still their main data storage, and it has 60+ years of legacy code on it that is not easily or quickly migrated to modern architecture.